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authorMichael S. Tsirkin <mst@redhat.com>2013-05-26 17:32:13 +0300
committerIngo Molnar <mingo@kernel.org>2013-05-28 09:41:11 +0200
commit114276ac0a3beb9c391a410349bd770653e185ce (patch)
treed5bfaac722054c5a576647edf8642058fae298a7 /mm/mempolicy.c
parent016be2e55d98aee0b97b94b200d6e0e110c8392a (diff)
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mm, sched: Drop voluntary schedule from might_fault()
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>
Diffstat (limited to 'mm/mempolicy.c')
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