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x86, mm: trace when an IPI is about to be sent

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When unmapping pages it is necessary to flush the TLB.  If that page was
accessed by another CPU then an IPI is used to flush the remote CPU.  That
is a lot of IPIs if kswapd is scanning and unmapping >100K pages per
second.

There already is a window between when a page is unmapped and when it is
TLB flushed.  This series increases the window so multiple pages can be
flushed using a single IPI.  This should be safe or the kernel is hosed
already.

Patch 1 simply made the rest of the series easier to write as ftrace
        could identify all the senders of TLB flush IPIS.

Patch 2 tracks what CPUs potentially map a PFN and then sends an IPI
        to flush the entire TLB.

Patch 3 tracks when there potentially are writable TLB entries that
        need to be batched differently

Patch 4 increases SWAP_CLUSTER_MAX to further batch flushes

The performance impact is documented in the changelogs but in the optimistic
case on a 4-socket machine the full series reduces interrupts from 900K
interrupts/second to 60K interrupts/second.

This patch (of 4):

It is easy to trace when an IPI is received to flush a TLB but harder to
detect what event sent it.  This patch makes it easy to identify the
source of IPIs being transmitted for TLB flushes on x86.

Signed-off-by: Mel Gorman <mgorman@suse.de>
Reviewed-by: Rik van Riel <riel@redhat.com>
Reviewed-by: Dave Hansen <dave.hansen@intel.com>
Acked-by: Ingo Molnar <mingo@kernel.org>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
This commit is contained in:
Mel Gorman 2015-09-04 15:47:29 -07:00 committed by Linus Torvalds
parent c47174fc36
commit 5b74283ab2
3 changed files with 4 additions and 1 deletions
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1
arch/x86/mm/tlb.c
View File

@ -140,6 +140,7 @@ void native_flush_tlb_others(const struct cpumask *cpumask,
info.flush_end = end;
count_vm_tlb_event(NR_TLB_REMOTE_FLUSH);
trace_tlb_flush(TLB_REMOTE_SEND_IPI, end - start);
if (is_uv_system()) {
unsigned int cpu;

1
include/linux/mm_types.h
View File

@ -554,6 +554,7 @@ enum tlb_flush_reason {
TLB_REMOTE_SHOOTDOWN,
TLB_LOCAL_SHOOTDOWN,
TLB_LOCAL_MM_SHOOTDOWN,
TLB_REMOTE_SEND_IPI,
NR_TLB_FLUSH_REASONS,
};

3
include/trace/events/tlb.h
View File

@ -11,7 +11,8 @@
EM( TLB_FLUSH_ON_TASK_SWITCH, "flush on task switch" ) \
EM( TLB_REMOTE_SHOOTDOWN, "remote shootdown" ) \
EM( TLB_LOCAL_SHOOTDOWN, "local shootdown" ) \
EMe( TLB_LOCAL_MM_SHOOTDOWN, "local mm shootdown" )
EM( TLB_LOCAL_MM_SHOOTDOWN, "local mm shootdown" ) \
EMe( TLB_REMOTE_SEND_IPI, "remote ipi send" )
/*
* First define the enums in TLB_FLUSH_REASON to be exported to userspace