114276ac0a
might_fault() is called from functions like copy_to_user() which most callers expect to be very fast, like a couple of instructions. So functions like memcpy_toiovec() call them many times in a loop. But might_fault() calls might_sleep() and with CONFIG_PREEMPT_VOLUNTARY this results in a function call. Let's not do this - just call __might_sleep() that produces a diagnostic for sleep within atomic, but drop might_preempt(). Here's a test sending traffic between the VM and the host, host is built with CONFIG_PREEMPT_VOLUNTARY: before: incoming: 7122.77 Mb/s outgoing: 8480.37 Mb/s after: incoming: 8619.24 Mb/s outgoing: 9455.42 Mb/s As a side effect, this fixes an issue pointed out by Ingo: might_fault might schedule differently depending on PROVE_LOCKING. Now there's no preemption point in both cases, so it's consistent. Signed-off-by: Michael S. Tsirkin <mst@redhat.com> Signed-off-by: Peter Zijlstra <peterz@infradead.org> Cc: Linus Torvalds <torvalds@linux-foundation.org> Cc: Andrew Morton <akpm@linux-foundation.org> Cc: Peter Zijlstra <a.p.zijlstra@chello.nl> Link: http://lkml.kernel.org/r/1369577426-26721-10-git-send-email-mst@redhat.com Signed-off-by: Ingo Molnar <mingo@kernel.org> |
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