Messages in this thread Patch in this message | | | Date | Sun, 26 May 2013 17:32:13 +0300 | From | "Michael S. Tsirkin" <> | Subject | [PATCH v3-resend 10/11] kernel: drop voluntary schedule from might_fault |
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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> --- include/linux/kernel.h | 2 +- mm/memory.c | 3 ++- 2 files changed, 3 insertions(+), 2 deletions(-)
diff --git a/include/linux/kernel.h b/include/linux/kernel.h index e96329c..c514c06 100644 --- a/include/linux/kernel.h +++ b/include/linux/kernel.h @@ -198,7 +198,7 @@ void might_fault(void); #else static inline void might_fault(void) { - might_sleep(); + __might_sleep(__FILE__, __LINE__, 0); } #endif diff --git a/mm/memory.c b/mm/memory.c index 6dc1882..c1f190f 100644 --- a/mm/memory.c +++ b/mm/memory.c @@ -4222,7 +4222,8 @@ void might_fault(void) if (segment_eq(get_fs(), KERNEL_DS)) return; - might_sleep(); + __might_sleep(__FILE__, __LINE__, 0); + /* * it would be nicer only to annotate paths which are not under * pagefault_disable, however that requires a larger audit and -- MST
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