Граф коммитов

51 Коммитов

Автор SHA1 Сообщение Дата
Alexander Duyck 1077fa36f2 arch: Add lightweight memory barriers dma_rmb() and dma_wmb()
There are a number of situations where the mandatory barriers rmb() and
wmb() are used to order memory/memory operations in the device drivers
and those barriers are much heavier than they actually need to be.  For
example in the case of PowerPC wmb() calls the heavy-weight sync
instruction when for coherent memory operations all that is really needed
is an lsync or eieio instruction.

This commit adds a coherent only version of the mandatory memory barriers
rmb() and wmb().  In most cases this should result in the barrier being the
same as the SMP barriers for the SMP case, however in some cases we use a
barrier that is somewhere in between rmb() and smp_rmb().  For example on
ARM the rmb barriers break down as follows:

  Barrier   Call     Explanation
  --------- -------- ----------------------------------
  rmb()     dsb()    Data synchronization barrier - system
  dma_rmb() dmb(osh) data memory barrier - outer sharable
  smp_rmb() dmb(ish) data memory barrier - inner sharable

These new barriers are not as safe as the standard rmb() and wmb().
Specifically they do not guarantee ordering between coherent and incoherent
memories.  The primary use case for these would be to enforce ordering of
reads and writes when accessing coherent memory that is shared between the
CPU and a device.

It may also be noted that there is no dma_mb().  Most architectures don't
provide a good mechanism for performing a coherent only full barrier without
resorting to the same mechanism used in mb().  As such there isn't much to
be gained in trying to define such a function.

Cc: Frederic Weisbecker <fweisbec@gmail.com>
Cc: Mathieu Desnoyers <mathieu.desnoyers@polymtl.ca>
Cc: Michael Ellerman <michael@ellerman.id.au>
Cc: Michael Neuling <mikey@neuling.org>
Cc: Russell King <linux@arm.linux.org.uk>
Cc: Geert Uytterhoeven <geert@linux-m68k.org>
Cc: Heiko Carstens <heiko.carstens@de.ibm.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Martin Schwidefsky <schwidefsky@de.ibm.com>
Cc: Tony Luck <tony.luck@intel.com>
Cc: Oleg Nesterov <oleg@redhat.com>
Cc: "Paul E. McKenney" <paulmck@linux.vnet.ibm.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Ingo Molnar <mingo@kernel.org>
Cc: David Miller <davem@davemloft.net>
Acked-by: Benjamin Herrenschmidt <benh@kernel.crashing.org>
Acked-by: Will Deacon <will.deacon@arm.com>
Signed-off-by: Alexander Duyck <alexander.h.duyck@redhat.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
2014-12-11 21:15:06 -05:00
Linus Torvalds c30110608c Merge branch 'core-rcu-for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip
Pull RCU updates from Ingo Molnar:
 "These are the main changes in this cycle:

    - Streamline RCU's use of per-CPU variables, shifting from "cpu"
      arguments to functions to "this_"-style per-CPU variable
      accessors.

    - signal-handling RCU updates.

    - real-time updates.

    - torture-test updates.

    - miscellaneous fixes.

    - documentation updates"

* 'core-rcu-for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip: (34 commits)
  rcu: Fix FIXME in rcu_tasks_kthread()
  rcu: More info about potential deadlocks with rcu_read_unlock()
  rcu: Optimize cond_resched_rcu_qs()
  rcu: Add sparse check for RCU_INIT_POINTER()
  documentation: memory-barriers.txt: Correct example for reorderings
  documentation: Add atomic_long_t to atomic_ops.txt
  documentation: Additional restriction for control dependencies
  documentation: Document RCU self test boot params
  rcutorture: Fix rcu_torture_cbflood() memory leak
  rcutorture: Remove obsolete kversion param in kvm.sh
  rcutorture: Remove stale test configurations
  rcutorture: Enable RCU self test in configs
  rcutorture: Add early boot self tests
  torture: Run Linux-kernel binary out of results directory
  cpu: Avoid puts_pending overflow
  rcu: Remove "cpu" argument to rcu_cleanup_after_idle()
  rcu: Remove "cpu" argument to rcu_prepare_for_idle()
  rcu: Remove "cpu" argument to rcu_needs_cpu()
  rcu: Remove "cpu" argument to rcu_note_context_switch()
  rcu: Remove "cpu" argument to rcu_preempt_check_callbacks()
  ...
2014-12-09 20:23:19 -08:00
Pranith Kumar 8ab8b3e183 documentation: memory-barriers.txt: Correct example for reorderings
Correct the example of memory orderings in memory-barriers.txt

Commit 615cc2c9cf "Documentation/memory-barriers.txt: fix important typo re
memory barriers" changed the assignment to x and y. Change the rest of the
example to match this change.

Reported-by: Ganesh Rapolu <ganesh.rapolu@hotmail.com>
Signed-off-by: Pranith Kumar <bobby.prani@gmail.com>
Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
2014-11-13 10:34:55 -08:00
Paul E. McKenney 8b19d1dead documentation: Additional restriction for control dependencies
Short-circuit booleans are not defences against compilers breaking
your intended control dependencies.

Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
Reviewed-by: Pranith Kumar <bobby.prani@gmail.com>
2014-11-13 10:34:53 -08:00
Will Deacon a8e0aead70 documentation: memory-barriers: clarify relaxed io accessor semantics
This patch extends the paragraph describing the relaxed read io accessors
so that the relaxed accessors are defined to be:

 - Ordered with respect to each other if accessing the same peripheral

 - Unordered with respect to normal memory accesses

 - Unordered with respect to LOCK/UNLOCK operations

Whilst many architectures will provide stricter semantics, ARM, Alpha and
PPC can achieve significant performance gains by taking advantage of some
or all of the above relaxations.

Cc: Randy Dunlap <rdunlap@infradead.org>
Cc: Benjamin Herrenschmidt <benh@kernel.crashing.org>
Cc: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
Cc: David Howells <dhowells@redhat.com>
Signed-off-by: Will Deacon <will.deacon@arm.com>
2014-10-20 18:49:18 +01:00
Paul E. McKenney 2456d2a617 memory-barriers: Fix description of 2-legged-if-based control dependencies
Sad to say, current compilers really will hoist identical stores from both
branches of an "if" statement to precede the conditional.  This commit
therefore updates the description of control dependencies to reflect this
ugly reality.

Reported-by: Pranith Kumar <bobby.prani@gmail.com>
Reported-by: Peter Zijlstra <peterz@infradead.org>
Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
2014-09-07 16:15:53 -07:00
Paul E. McKenney efdcd51a4d memory-barriers: Retain barrier() in fold-to-zero example
The transformation in the fold-to-zero example incorrectly omits the
barrier() directive.  This commit therefore adds it back in.

Reported-by: Pranith Kumar <pranith@gatech.edu>
Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
2014-09-07 16:15:52 -07:00
Paul E. McKenney 5646f7acc9 memory-barriers: Fix control-ordering no-transitivity example
The control-ordering example demonstrating lack of transitivity had
multiple problems.  This commit fixes them.

Reported-by: Nikolay Samofatov <nikolay.samofatov@gmail.com>
Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
Reviewed-by: Pranith Kumar <bobby.prani@gmail.com>
2014-09-07 16:15:41 -07:00
Paul E. McKenney 128ea442b1 documentation: Add acquire/release barriers to pairing rules
It is possible to pair acquire and release barriers with other barriers,
so this commit adds them to the list in the SMP barrier pairing section.

Reported-by: Lai Jiangshan <laijs@cn.fujitsu.com>
Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
Reviewed-by: Tejun Heo <tj@kernel.org>
Reviewed-by: Josh Triplett <josh@joshtriplett.org>
[ paulmck: Updated pairing discussion as suggested by Peter Zijlstra. ]
2014-07-08 08:32:51 -07:00
Paul E. McKenney 5726ce06ad documentation: Clarify wake-up/memory-barrier relationship
This commit adds an example demonstrating that if a wake_up() doesn't
actually wake something up, no memory ordering is provided.

Reported-by: Peter Zijlstra <peterz@infradead.org>
Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
Reviewed-by: Josh Triplett <josh@joshtriplett.org>
Reviewed-by: Lai Jiangshan <laijs@cn.fujitsu.com>
Acked-by: Peter Zijlstra <peterz@infradead.org>
2014-07-08 08:13:03 -07:00
Alexey Dobriyan 615cc2c9cf Documentation/memory-barriers.txt: fix important typo re memory barriers
Examples introducing neccesity of RMB+WMP pair reads as

        A=3	READ B
        www	rrrrrr
        B=4	READ A

Note the opposite order of reads vs writes.

But the first example without barriers reads as

        A=3	READ A
        B=4	READ B

There are 4 outcomes in the first example.

But if someone new to the concept tries to insert barriers like this:

        A=3	READ A
        www	rrrrrr
        B=4	READ B

he will still get all 4 possible outcomes, because "READ A" is first.

All this can be utterly confusing because barrier pair seems to be
superfluous.  In short, fixup first example to match latter examples
with barriers.

Signed-off-by: Alexey Dobriyan <adobriyan@gmail.com>
Cc: David Howells <dhowells@redhat.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2014-06-06 16:08:11 -07:00
Peter Zijlstra 1b15611e1c arch,doc: Convert smp_mb__*()
Update the documentation to reflect the change of barrier primitives.

Signed-off-by: Peter Zijlstra <peterz@infradead.org>
Reviewed-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
Acked-by: David Howells <dhowells@redhat.com>
Link: http://lkml.kernel.org/n/tip-xslfehiga1twbk5uk94rij1e@git.kernel.org
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Randy Dunlap <rdunlap@infradead.org>
Cc: linux-doc@vger.kernel.org
Cc: linux-kernel@vger.kernel.org
Signed-off-by: Ingo Molnar <mingo@kernel.org>
2014-04-18 14:20:48 +02:00
Linus Torvalds 159d8133d0 Merge branch 'for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/jikos/trivial
Pull trivial tree updates from Jiri Kosina:
 "Usual rocket science -- mostly documentation and comment updates"

* 'for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/jikos/trivial:
  sparse: fix comment
  doc: fix double words
  isdn: capi: fix "CAPI_VERSION" comment
  doc: DocBook: Fix typos in xml and template file
  Bluetooth: add module name for btwilink
  driver core: unexport static function create_syslog_header
  mmc: core: typo fix in printk specifier
  ARM: spear: clean up editing mistake
  net-sysfs: fix comment typo 'CONFIG_SYFS'
  doc: Insert MODULE_ in module-signing macros
  Documentation: update URL to hfsplus Technote 1150
  gpio: update path to documentation
  ixgbe: Fix format string in ixgbe_fcoe.
  Kconfig: Remove useless "default N" lines
  user_namespace.c: Remove duplicated word in comment
  CREDITS: fix formatting
  treewide: Fix typo in Documentation/DocBook
  mm: Fix warning on make htmldocs caused by slab.c
  ata: ata-samsung_cf: cleanup in header file
  idr: remove unused prototype of idr_free()
2014-04-02 16:23:38 -07:00
Masanari Iida df5cbb2783 doc: fix double words
Fix double words "the the" in various files
within Documentations.

Signed-off-by: Masanari Iida <standby24x7@gmail.com>
Signed-off-by: Jiri Kosina <jkosina@suse.cz>
2014-03-21 13:16:58 +01:00
Paul E. McKenney 8dd853d7b6 Documentation/memory-barriers.txt: Clarify release/acquire ordering
This commit fixes a couple of typos and clarifies what happens when
the CPU chooses to execute a later lock acquisition before a prior
lock release, in particular, why deadlock is avoided.

Reported-by: Peter Hurley <peter@hurleysoftware.com>
Reported-by: James Bottomley <James.Bottomley@HansenPartnership.com>
Reported-by: Stefan Richter <stefanr@s5r6.in-berlin.de>
Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
2014-02-24 08:37:29 -08:00
Paul E. McKenney 9b2b3bf531 Documentation/memory-barriers.txt: Need barriers() for some control dependencies
Current compilers can "speculate" stores in the case where both legs
of the "if" statement start with identical stores.  Because the stores
are identical, the compiler knows that the store will unconditionally
execute regardless of the "if" condition, and so the compiler is within
its rights to hoist the store to precede the condition.  Such hoisting
destroys the control-dependency ordering.  This ordering can be restored
by placing a barrier() at the beginning of each leg of the "if" statement.
This commit adds this requirement to the control-dependencies section.

Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
2014-02-17 14:56:09 -08:00
Paul E. McKenney 586dd56a4c Documentation/memory-barriers.txt: Conditional must use prior load
A control dependency consists of a load, a conditional that depends on
that load, and a store.  This commit emphasizes this point in the
summary.

Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
Reviewed-by: Josh Triplett <josh@joshtriplett.org>
2014-02-17 14:56:07 -08:00
Paul E. McKenney 449f7413c8 Documentation/memory-barriers.txt: ACCESS_ONCE() provides cache coherence
The ACCESS_ONCE() primitive provides cache coherence, but the
documentation does not clearly state this.  This commit therefore upgrades
the documentation.

Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
Reviewed-by: Josh Triplett <josh@joshtriplett.org>
2014-02-17 14:56:06 -08:00
Peter Zijlstra 2e4f5382d1 locking/doc: Rename LOCK/UNLOCK to ACQUIRE/RELEASE
The LOCK and UNLOCK barriers as described in our barrier document are
generally known as ACQUIRE and RELEASE barriers in other literature.

Since we plan to introduce the acquire and release nomenclature in
generic kernel primitives we should amend the document to avoid
confusion as to what an acquire/release means.

Reviewed-by: "Paul E. McKenney" <paulmck@linux.vnet.ibm.com>
Signed-off-by: Peter Zijlstra <peterz@infradead.org>
Acked-by: Mathieu Desnoyers <mathieu.desnoyers@polymtl.ca>
Cc: Benjamin Herrenschmidt <benh@kernel.crashing.org>
Cc: Frederic Weisbecker <fweisbec@gmail.com>
Cc: Michael Ellerman <michael@ellerman.id.au>
Cc: Michael Neuling <mikey@neuling.org>
Cc: Russell King <linux@arm.linux.org.uk>
Cc: Geert Uytterhoeven <geert@linux-m68k.org>
Cc: Heiko Carstens <heiko.carstens@de.ibm.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Martin Schwidefsky <schwidefsky@de.ibm.com>
Cc: Victor Kaplansky <VICTORK@il.ibm.com>
Cc: Tony Luck <tony.luck@intel.com>
Cc: Oleg Nesterov <oleg@redhat.com>
Link: http://lkml.kernel.org/r/20131217092435.GC21999@twins.programming.kicks-ass.net
Signed-off-by: Ingo Molnar <mingo@kernel.org>
2014-01-12 10:37:13 +01:00
Paul E. McKenney 17eb88e068 Documentation/memory-barriers.txt: Downgrade UNLOCK+BLOCK
Historically, an UNLOCK+LOCK pair executed by one CPU, by one
task, or on a given lock variable has implied a full memory
barrier.  In a recent LKML thread, the wisdom of this historical
approach was called into question:
http://www.spinics.net/lists/linux-mm/msg65653.html, in part due
to the memory-order complexities of low-handoff-overhead queued
locks on x86 systems.

This patch therefore removes this guarantee from the
documentation, and further documents how to restore it via a new
smp_mb__after_unlock_lock() primitive.

Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
Reviewed-by: Peter Zijlstra <a.p.zijlstra@chello.nl>
Cc: <linux-arch@vger.kernel.org>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Andrew Morton <akpm@linux-foundation.org>
Link: http://lkml.kernel.org/r/1386799151-2219-6-git-send-email-paulmck@linux.vnet.ibm.com
Signed-off-by: Ingo Molnar <mingo@kernel.org>
2013-12-16 11:36:15 +01:00
Paul E. McKenney 692118dac4 Documentation/memory-barriers.txt: Document ACCESS_ONCE()
The situations in which ACCESS_ONCE() is required are not well
documented, so this commit adds some verbiage to
memory-barriers.txt.

Reported-by: Peter Zijlstra <peterz@infradead.org>
Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
Reviewed-by: Josh Triplett <josh@joshtriplett.org>
Reviewed-by: Peter Zijlstra <a.p.zijlstra@chello.nl>
Cc: <linux-arch@vger.kernel.org>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Andrew Morton <akpm@linux-foundation.org>
Link: http://lkml.kernel.org/r/1386799151-2219-4-git-send-email-paulmck@linux.vnet.ibm.com
Signed-off-by: Ingo Molnar <mingo@kernel.org>
2013-12-16 11:36:12 +01:00
Peter Zijlstra 18c03c6144 Documentation/memory-barriers.txt: Prohibit speculative writes
No SMP architecture currently supporting Linux allows
speculative writes, so this commit updates
Documentation/memory-barriers.txt to prohibit them in Linux core
code.  It also records restrictions on their use.

Signed-off-by: Peter Zijlstra <peterz@infradead.org>
Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
Reviewed-by: Josh Triplett <josh@joshtriplett.org>
Reviewed-by: Peter Zijlstra <a.p.zijlstra@chello.nl>
Cc: <linux-arch@vger.kernel.org>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Andrew Morton <akpm@linux-foundation.org>
Link: http://lkml.kernel.org/r/1386799151-2219-3-git-send-email-paulmck@linux.vnet.ibm.com
[ Paul modified the original patch from Peter. ]
Signed-off-by: Ingo Molnar <mingo@kernel.org>
2013-12-16 11:36:11 +01:00
Paul E. McKenney fb2b581968 Documentation/memory-barriers.txt: Add long atomic examples to memory-barriers.txt
Although the atomic_long_t functions are quite useful, they are
a bit obscure.  This commit therefore adds the common ones
alongside their atomic_t counterparts in
Documentation/memory-barriers.txt.

Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
Reviewed-by: Josh Triplett <josh@joshtriplett.org>
Reviewed-by: Peter Zijlstra <a.p.zijlstra@chello.nl>
Cc: <linux-arch@vger.kernel.org>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Andrew Morton <akpm@linux-foundation.org>
Link: http://lkml.kernel.org/r/1386799151-2219-2-git-send-email-paulmck@linux.vnet.ibm.com
Signed-off-by: Ingo Molnar <mingo@kernel.org>
2013-12-16 11:36:09 +01:00
Paul E. McKenney 2ecf810121 Documentation/memory-barriers.txt: Add needed ACCESS_ONCE() calls to memory-barriers.txt
The Documentation/memory-barriers.txt file was written before
the need for ACCESS_ONCE() was fully appreciated.  It therefore
contains no ACCESS_ONCE() calls, which can be a problem when
people lift examples from it.  This commit therefore adds
ACCESS_ONCE() calls.

Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
Reviewed-by: Josh Triplett <josh@joshtriplett.org>
Reviewed-by: Peter Zijlstra <a.p.zijlstra@chello.nl>
Cc: <linux-arch@vger.kernel.org>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Andrew Morton <akpm@linux-foundation.org>
Link: http://lkml.kernel.org/r/1386799151-2219-1-git-send-email-paulmck@linux.vnet.ibm.com
Signed-off-by: Ingo Molnar <mingo@kernel.org>
2013-12-16 11:36:08 +01:00
Ingo Molnar e0edc78f25 Documentation/memory-barriers.txt: Fix a typo in the data dependency description
This typo has been there forever, it is 7.5 years old, looks like this
section of our memory ordering documentation is a place where most eyes
are glazed over already ;-)

[ Also fix some stray spaces and stray tabs while at it, shrinking the
  file by 49 bytes. Visual output unchanged. ]

Cc: Peter Zijlstra <a.p.zijlstra@chello.nl>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Andrew Morton <akpm@linux-foundation.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
Link: http://lkml.kernel.org/n/tip-gncea9cb8igosblizfqMXrie@git.kernel.org
Signed-off-by: Ingo Molnar <mingo@kernel.org>
2013-11-22 11:46:12 +01:00
Paul E. McKenney 45c8a36a55 doc: Fix memory-barrier control-dependency example
Each control-dependency example needs its barriers between the "if"
condition and the body of the "if" because a control dependency is
a dependency induced by a branch.  This commit makes the needed
adjustment.

Reported-by: Yongming Shen <symingz@gmail.com>
Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
Reviewed-by: Josh Triplett <josh@joshtriplett.org>
2013-08-19 21:39:42 -07:00
Richard Braun 7e8b1e78ea Documentation: Memory barrier semantics of atomic_xchg()
Add atomic_xchg() to documentation for atomic operations and
memory barriers.

Signed-off-by: Richard Braun <rbraun@sceen.net>
Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
Reviewed-by: Josh Triplett <josh@joshtriplett.org>
2013-01-08 14:14:55 -08:00
Paul E. McKenney f191eec588 Documentation: Fix memory-barriers.txt example
This commit fixes a broken example of overlapping stores in the
Documentation/memory-barriers.txt file.

Reported-by: Nikunj A Dadhania <nikunj@linux.vnet.ibm.com>
Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
2012-10-23 14:44:46 -07:00
Paul Bolle 395cf9691d doc: fix broken references
There are numerous broken references to Documentation files (in other
Documentation files, in comments, etc.). These broken references are
caused by typo's in the references, and by renames or removals of the
Documentation files. Some broken references are simply odd.

Fix these broken references, sometimes by dropping the irrelevant text
they were part of.

Signed-off-by: Paul Bolle <pebolle@tiscali.nl>
Signed-off-by: Jiri Kosina <jkosina@suse.cz>
2011-09-27 18:08:04 +02:00
Paul E. McKenney 241e6663b5 smp: Document transitivity for memory barriers.
Transitivity is guaranteed only for full memory barriers (smp_mb()).

Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
2011-03-04 08:05:49 -08:00
David Howells 90fddabf58 Document Linux's circular buffering capabilities
Document the circular buffering capabilities available in Linux.

Signed-off-by: David Howells <dhowells@redhat.com>
Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
Reviewed-by: Randy Dunlap <rdunlap@xenotime.net>
Reviewed-by: Stefan Richter <stefanr@s5r6.in-berlin.de>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2010-03-24 16:31:22 -07:00
David Howells 50fa610a3b sched: Document memory barriers implied by sleep/wake-up primitives
Add a section to the memory barriers document to note the implied
memory barriers of sleep primitives (set_current_state() and wrappers)
and wake-up primitives (wake_up() and co.).

Also extend the in-code comments on the wake_up() functions to note
these implied barriers.

[ Impact: add documentation ]

Signed-off-by: David Howells <dhowells@redhat.com>
Cc: Oleg Nesterov <oleg@redhat.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Andrew Morton <akpm@linux-foundation.org>
LKML-Reference: <20090428140138.1192.94723.stgit@warthog.procyon.org.uk>
Signed-off-by: Ingo Molnar <mingo@elte.hu>
2009-04-29 14:15:55 +02:00
Nick Piggin 73f10281ea read_barrier_depends arch fixlets
read_barrie_depends has always been a noop (not a compiler barrier) on all
architectures except SMP alpha. This brings UP alpha and frv into line with all
other architectures, and fixes incorrect documentation.

Signed-off-by: Nick Piggin <npiggin@suse.de>
Acked-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2008-05-14 10:05:18 -07:00
Randy Dunlap 4b5ff46923 PCI: doc/pci: create Documentation/PCI/ and move files into it
Create Documentation/PCI/ and move PCI-related files to it.
Fix a few instances of trailing whitespace.
Update references to the new file locations.

Signed-off-by: Randy Dunlap <randy.dunlap@oracle.com>
Cc: Jesse Barnes <jbarnes@virtuousgeek.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>
2008-04-20 21:46:51 -07:00
Oleg Nesterov 02c608c1fe documentation: atomic_add_unless() doesn't imply mb() on failure
(sorry for being offtpoic, but while experts are here...)

A "typical" implementation of atomic_add_unless() can return 0 immediately
after the first atomic_read() (before doing cmpxchg). In that case it doesn't
provide any barrier semantics. See include/asm-ia64/atomic.h as an example.

We should either change the implementation, or fix the docs.

Signed-off-by: Oleg Nesterov <oleg@tv-sign.ru>
Acked-by: Nick Piggin <npiggin@suse.de>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2008-02-23 17:52:36 -08:00
Nick Piggin 26333576fd bitops: introduce lock ops
Introduce test_and_set_bit_lock / clear_bit_unlock bitops with lock semantics.
Convert all architectures to use the generic implementation.

Signed-off-by: Nick Piggin <npiggin@suse.de>
Acked-By: David Howells <dhowells@redhat.com>
Cc: Richard Henderson <rth@twiddle.net>
Cc: Ivan Kokshaysky <ink@jurassic.park.msu.ru>
Cc: Russell King <rmk@arm.linux.org.uk>
Cc: Haavard Skinnemoen <hskinnemoen@atmel.com>
Cc: Bryan Wu <bryan.wu@analog.com>
Cc: Mikael Starvik <starvik@axis.com>
Cc: David Howells <dhowells@redhat.com>
Cc: Yoshinori Sato <ysato@users.sourceforge.jp>
Cc: "Luck, Tony" <tony.luck@intel.com>
Cc: Hirokazu Takata <takata@linux-m32r.org>
Cc: Geert Uytterhoeven <geert@linux-m68k.org>
Cc: Roman Zippel <zippel@linux-m68k.org>
Cc: Greg Ungerer <gerg@uclinux.org>
Cc: Ralf Baechle <ralf@linux-mips.org>
Cc: Kyle McMartin <kyle@mcmartin.ca>
Cc: Matthew Wilcox <willy@debian.org>
Cc: Paul Mackerras <paulus@samba.org>
Cc: Benjamin Herrenschmidt <benh@kernel.crashing.org>
Cc: Heiko Carstens <heiko.carstens@de.ibm.com>
Cc: Martin Schwidefsky <schwidefsky@de.ibm.com>
Cc: Paul Mundt <lethal@linux-sh.org>
Cc: Kazumoto Kojima <kkojima@rr.iij4u.or.jp>
Cc: Richard Curnow <rc@rc0.org.uk>
Cc: William Lee Irwin III <wli@holomorphy.com>
Cc: "David S. Miller" <davem@davemloft.net>
Cc: Jeff Dike <jdike@addtoit.com>
Cc: Paolo 'Blaisorblade' Giarrusso <blaisorblade@yahoo.it>
Cc: Miles Bader <uclinux-v850@lsi.nec.co.jp>
Cc: Andi Kleen <ak@muc.de>
Cc: Chris Zankel <chris@zankel.net>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2007-10-18 14:37:29 -07:00
Jarek Poplawski 81fc632355 Documentation/memory-barriers.txt: various fixes
Fix various grammatical issues in Documentation/memory-barriers.txt.

Cc: "Robert P. J. Day" <rpjday@mindspring.com>
Signed-off-by: Jarek Poplawski <jarkao2@o2.pl>
Signed-off-by: David Howells <dhowells@redhat.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2007-05-23 20:14:15 -07:00
Matt LaPlante fa00e7e152 Fix typos in /Documentation : 'T''
This patch fixes typos in various Documentation txts. The patch addresses some
+words starting with the letter 'T'.

Signed-off-by: Matt LaPlante <kernel1@cyberdogtech.com>
Acked-by: Randy Dunlap <rdunlap@xenotime.net>
Signed-off-by: Adrian Bunk <bunk@stusta.de>
2006-11-30 04:55:36 +01:00
Oleg Nesterov 75b2bd55bd [PATCH] A minor fix for set_mb() in Documentation/memory-barriers.txt
set_mb() is used by set_current_state() which needs mb(), not wmb().  I
think it would be right to assume that set_mb() implies mb(), all arches
seem to do just this.

Signed-off-by: Oleg Nesterov <oleg@tv-sign.ru>
Acked-by: David Howells <dhowells@redhat.com>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>
2006-11-08 18:29:22 -08:00
Paolo 'Blaisorblade' Giarrusso 3fda982c50 [PATCH] fix typo in memory barrier docs
Fix cut'n'paste typo - &a and &b are used in other examples, in this one
the doc uses &u and &v.

Signed-off-by: Paolo 'Blaisorblade' Giarrusso <blaisorblade@yahoo.it>
Acked-by: David Howells <dhowells@redhat.com>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>
2006-10-20 10:26:35 -07:00
Paolo Ornati 670e9f34ee Documentation: remove duplicated words
Remove many duplicated words under Documentation/ and do other small
cleanups.

Examples:
        "and and" --> "and"
        "in in" --> "in"
        "the the" --> "the"
        "the the" --> "to the"
        ...

Signed-off-by: Paolo Ornati <ornati@fastwebnet.it>
Signed-off-by: Adrian Bunk <bunk@stusta.de>
2006-10-03 22:57:56 +02:00
Matt LaPlante 3f6dee9b2a Fix some typos in Documentation/: 'A'
This patch fixes typos in various Documentation txts.
This patch addresses some words starting with the letter 'A'.

Signed-off-by: Matt LaPlante <kernel1@cyberdogtech.com>
Acked-by: Randy Dunlap <rdunlap@xenotime.net>
Acked-by: Alan Cox <alan@redhat.com>
Signed-off-by: Adrian Bunk <bunk@stusta.de>
2006-10-03 22:45:33 +02:00
Steven Rostedt f92213bae0 [PATCH] remove set_wmb - doc update
This patch removes the reference to set_wmb from memory-barriers.txt
since it shouldn't be used.

Signed-off-by: Steven Rostedt <rostedt@goodmis.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>
2006-07-14 21:56:14 -07:00
Adrian Bunk 80f7228b59 typo fixes: occuring -> occurring
Signed-off-by: Adrian Bunk <bunk@stusta.de>
2006-06-30 18:27:16 +02:00
David Howells 6bc392741d [PATCH] Corrections to memory barrier doc
Apply some small corrections to the memory barrier document, as contributed by:

	Christoph Lameter <clameter@sgi.com>
	Kirill Smelkov <kirr@mns.spb.ru>
	Randy Dunlap <rdunlap@xenotime.net>

Signed-off-by: David Howells <dhowells@redhat.com>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>
2006-06-25 10:01:24 -07:00
David Howells 2b94895b92 [PATCH] Another couple of alterations to the memory barrier doc
Make another couple of alterations to the memory barrier document following
suggestions by Alan Stern and in co-operation with Paul McKenney:

 (*) Rework the point of introduction of memory barriers and the description
     of what they are to reiterate why they're needed.

 (*) Modify a statement about the use of data dependency barriers to note that
     other barriers can be used instead (as they imply DD-barriers).

Signed-off-by: David Howells <dhowells@redhat.com>
Acked-By: Paul E. McKenney <paulmck@us.ibm.com>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>
2006-06-25 10:01:19 -07:00
David Howells 670bd95e04 [PATCH] Further alterations for memory barrier document
From: David Howells <dhowells@redhat.com>

Apply some alterations to the memory barrier document that I worked out
with Paul McKenney of IBM, plus some of the alterations suggested by Alan
Stern.

The following changes were made:

 (*) One of the examples given for what can happen with overlapping memory
     barriers was wrong.

 (*) The description of general memory barriers said that a general barrier is
     a combination of a read barrier and a write barrier.  This isn't entirely
     true: it implies both, but is more than a combination of both.

 (*) The first example in the "SMP Barrier Pairing" section was wrong: the
     loads around the read barrier need to touch the memory locations in the
     opposite order to the stores around the write barrier.

 (*) Added a note to make explicit that the loads should be in reverse order to
     the stores.

 (*) Adjusted the diagrams in the "Examples Of Memory Barrier Sequences"
     section to make them clearer.  Added a couple of diagrams to make it more
     clear as to how it could go wrong without the barrier.

 (*) Added a section on memory speculation.

 (*) Dropped any references to memory allocation routines doing memory
     barriers.  They may do sometimes, but it can't be relied on.  This may be
     worthy of further documentation later.

 (*) Made the fact that a LOCK followed by an UNLOCK should not be considered a
     full memory barrier more explicit and gave an example.

Signed-off-by: David Howells <dhowells@redhat.com>
Acked-by: Paul E. McKenney <paulmck@us.ibm.com>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>
2006-06-10 11:02:05 -07:00
Aneesh Kumar 79afecfaab [PATCH] Fix typos in Documentation/memory-barriers.txt
Fix some typos in Documentation/memory-barriers.txt

Signed-off-by: Aneesh Kumar K.V <aneesh.kumar@gmail.com>
Cc: David Howells <dhowells@redhat.com>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>
2006-05-15 11:20:58 -07:00
David Howells c14038c39d [PATCH] Improve data-dependency memory barrier example in documentation
In the memory barrier document, improve the example of the data dependency
barrier situation by:

 (1) showing the initial values of the variables involved; and

 (2) repeating the instruction sequence description, this time with the data
     dependency barrier actually shown to make it clear what the revised
     sequence actually is.

Signed-off-by: David Howells <dhowells@redhat.com>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>
2006-04-11 06:18:44 -07:00
David Howells dbc8700e27 [PATCH] Fix memory barrier docs wrt atomic ops
Fix the memory barrier documentation to attempt to describe atomic ops
correctly.

atomic_t ops that return a value _do_ imply smp_mb() either side, and so
don't actually require smp_mb__*_atomic_*() special barriers.

Also explains why special barriers exist in addition to normal barriers.

Further fix the memory barrier documents to portray bitwise operation
memory barrier effects correctly following Nick Piggin's comments.

It makes the point that any atomic op that both modifies some state in
memory and returns information on that state implies memory barriers on
both sides.

Signed-off-by: David Howells <dhowells@redhat.com>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>
2006-04-11 06:18:44 -07:00