Commit 5b74283a authored by Mel Gorman's avatar Mel Gorman Committed by Linus Torvalds

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

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: default avatarMel Gorman <mgorman@suse.de>
Reviewed-by: default avatarRik van Riel <riel@redhat.com>
Reviewed-by: default avatarDave Hansen <dave.hansen@intel.com>
Acked-by: default avatarIngo Molnar <mingo@kernel.org>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Signed-off-by: default avatarAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: default avatarLinus Torvalds <torvalds@linux-foundation.org>
parent c47174fc
...@@ -140,6 +140,7 @@ void native_flush_tlb_others(const struct cpumask *cpumask, ...@@ -140,6 +140,7 @@ void native_flush_tlb_others(const struct cpumask *cpumask,
info.flush_end = end; info.flush_end = end;
count_vm_tlb_event(NR_TLB_REMOTE_FLUSH); count_vm_tlb_event(NR_TLB_REMOTE_FLUSH);
trace_tlb_flush(TLB_REMOTE_SEND_IPI, end - start);
if (is_uv_system()) { if (is_uv_system()) {
unsigned int cpu; unsigned int cpu;
......
...@@ -554,6 +554,7 @@ enum tlb_flush_reason { ...@@ -554,6 +554,7 @@ enum tlb_flush_reason {
TLB_REMOTE_SHOOTDOWN, TLB_REMOTE_SHOOTDOWN,
TLB_LOCAL_SHOOTDOWN, TLB_LOCAL_SHOOTDOWN,
TLB_LOCAL_MM_SHOOTDOWN, TLB_LOCAL_MM_SHOOTDOWN,
TLB_REMOTE_SEND_IPI,
NR_TLB_FLUSH_REASONS, NR_TLB_FLUSH_REASONS,
}; };
......
...@@ -11,7 +11,8 @@ ...@@ -11,7 +11,8 @@
EM( TLB_FLUSH_ON_TASK_SWITCH, "flush on task switch" ) \ EM( TLB_FLUSH_ON_TASK_SWITCH, "flush on task switch" ) \
EM( TLB_REMOTE_SHOOTDOWN, "remote shootdown" ) \ EM( TLB_REMOTE_SHOOTDOWN, "remote shootdown" ) \
EM( TLB_LOCAL_SHOOTDOWN, "local 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 * First define the enums in TLB_FLUSH_REASON to be exported to userspace
......
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