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Max Gurtovoy 5c82c94b0b virtio-blk: avoid preallocating big SGL for data
[ Upstream commit 02746e26c3 ]

No need to pre-allocate a big buffer for the IO SGL anymore. If a device
has lots of deep queues, preallocation for the sg list can consume
substantial amounts of memory. For HW virtio-blk device, nr_hw_queues
can be 64 or 128 and each queue's depth might be 128. This means the
resulting preallocation for the data SGLs is big.

Switch to runtime allocation for SGL for lists longer than 2 entries.
This is the approach used by NVMe drivers so it should be reasonable for
virtio block as well. Runtime SGL allocation has always been the case
for the legacy I/O path so this is nothing new.

The preallocated small SGL depends on SG_CHAIN so if the ARCH doesn't
support SG_CHAIN, use only runtime allocation for the SGL.

Re-organize the setup of the IO request to fit the new sg chain
mechanism.

No performance degradation was seen (fio libaio engine with 16 jobs and
128 iodepth):

IO size      IOPs Rand Read (before/after)         IOPs Rand Write (before/after)
--------     ---------------------------------    ----------------------------------
512B          318K/316K                                    329K/325K

4KB           323K/321K                                    353K/349K

16KB          199K/208K                                    250K/275K

128KB         36K/36.1K                                    39.2K/41.7K

Signed-off-by: Max Gurtovoy <mgurtovoy@nvidia.com>
Reviewed-by: Israel Rukshin <israelr@nvidia.com>
Link: https://lore.kernel.org/r/20210901131434.31158-1-mgurtovoy@nvidia.com
Reviewed-by: Feng Li <lifeng1519@gmail.com>
Reviewed-by: Stefan Hajnoczi <stefanha@redhat.com>
Tested-by: Stefan Hajnoczi <stefanha@redhat.com>
Reviewed-by: Christoph Hellwig <hch@lst.de>
Signed-off-by: Arnd Bergmann <arnd@arndb.de> # kconfig fixups
Signed-off-by: Michael S. Tsirkin <mst@redhat.com>
Signed-off-by: Sasha Levin <sashal@kernel.org>
2022-07-12 16:34:56 +02:00
Documentation docs: update mapping documentation 2022-07-02 16:41:15 +02:00
LICENSES LICENSES/dual/CC-BY-4.0: Git rid of "smart quotes" 2021-07-15 06:31:24 -06:00
arch s390/setup: preserve memory at OLDMEM_BASE and OLDMEM_SIZE 2022-07-12 16:34:56 +02:00
block block: Fix handling of offline queues in blk_mq_alloc_request_hctx() 2022-06-22 14:22:02 +02:00
certs certs/blacklist_hashes.c: fix const confusion in certs blacklist 2022-06-22 14:22:01 +02:00
crypto crypto: memneq - move into lib/ 2022-06-22 14:22:03 +02:00
drivers virtio-blk: avoid preallocating big SGL for data 2022-07-12 16:34:56 +02:00
fs btrfs: fix deadlock between chunk allocation and chunk btree modifications 2022-07-12 16:34:52 +02:00
include netfilter: nft_payload: support for inner header matching / mangling 2022-07-12 16:34:55 +02:00
init Kconfig: Add option for asm goto w/ tied outputs to workaround clang-13 bug 2022-06-09 10:23:26 +02:00
ipc ipc/mqueue: use get_tree_nodev() in mqueue_get_tree() 2022-06-09 10:23:10 +02:00
kernel bpf: Stop caching subprog index in the bpf_pseudo_func insn 2022-07-12 16:34:54 +02:00
lib crypto: memneq - move into lib/ 2022-06-22 14:22:03 +02:00
mm mm/filemap: fix UAF in find_lock_entries 2022-07-12 16:34:47 +02:00
net netfilter: nft_payload: don't allow th access for fragments 2022-07-12 16:34:56 +02:00
samples samples/landlock: Format with clang-format 2022-06-09 10:23:23 +02:00
scripts modpost: fix section mismatch check for exported init/exit sections 2022-06-29 09:03:31 +02:00
security fs: support mapped mounts of mapped filesystems 2022-07-02 16:41:17 +02:00
sound ASoC: rt5682: Fix deadlock on resume 2022-07-12 16:34:55 +02:00
tools Revert "selftests/bpf: Add test for bpf_timer overwriting crash" 2022-07-12 16:34:47 +02:00
usr usr/include/Makefile: add linux/nfc.h to the compile-test coverage 2022-02-01 17:27:15 +01:00
virt KVM: avoid NULL pointer dereference in kvm_dirty_ring_push 2022-04-13 20:59:26 +02:00
.clang-format clang-format: Update with the latest for_each macro list 2021-05-12 23:32:39 +02:00
.cocciconfig scripts: add Linux .cocciconfig for coccinelle 2016-07-22 12:13:39 +02:00
.get_maintainer.ignore Opt out of scripts/get_maintainer.pl 2019-05-16 10:53:40 -07:00
.gitattributes .gitattributes: use 'dts' diff driver for dts files 2019-12-04 19:44:11 -08:00
.gitignore .gitignore: ignore only top-level modules.builtin 2021-05-02 00:43:35 +09:00
.mailmap mailmap: add Andrej Shadura 2021-10-18 20:22:03 -10:00
COPYING COPYING: state that all contributions really are covered by this file 2020-02-10 13:32:20 -08:00
CREDITS MAINTAINERS: Move Daniel Drake to credits 2021-09-21 08:34:58 +03:00
Kbuild kbuild: rename hostprogs-y/always to hostprogs/always-y 2020-02-04 01:53:07 +09:00
Kconfig kbuild: ensure full rebuild when the compiler is updated 2020-05-12 13:28:33 +09:00
MAINTAINERS Input: goodix - add a goodix.h header file 2022-07-12 16:34:51 +02:00
Makefile Linux 5.15.53 2022-07-07 17:53:35 +02:00
README Drop all 00-INDEX files from Documentation/ 2018-09-09 15:08:58 -06:00

README

Linux kernel
============

There are several guides for kernel developers and users. These guides can
be rendered in a number of formats, like HTML and PDF. Please read
Documentation/admin-guide/README.rst first.

In order to build the documentation, use ``make htmldocs`` or
``make pdfdocs``.  The formatted documentation can also be read online at:

    https://www.kernel.org/doc/html/latest/

There are various text files in the Documentation/ subdirectory,
several of them using the Restructured Text markup notation.

Please read the Documentation/process/changes.rst file, as it contains the
requirements for building and running the kernel, and information about
the problems which may result by upgrading your kernel.