From 5b74283ab251b9db55cbbe31d19ca72482103290 Mon Sep 17 00:00:00 2001 From: Mel Gorman Date: Fri, 4 Sep 2015 15:47:29 -0700 Subject: [PATCH] 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: Mel Gorman Reviewed-by: Rik van Riel Reviewed-by: Dave Hansen Acked-by: Ingo Molnar Cc: Linus Torvalds Signed-off-by: Andrew Morton Signed-off-by: Linus Torvalds --- arch/x86/mm/tlb.c | 1 + include/linux/mm_types.h | 1 + include/trace/events/tlb.h | 3 ++- 3 files changed, 4 insertions(+), 1 deletion(-) diff --git a/arch/x86/mm/tlb.c b/arch/x86/mm/tlb.c index 90b924acd982..8ddb5d0d66fb 100644 --- a/arch/x86/mm/tlb.c +++ b/arch/x86/mm/tlb.c @@ -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; diff --git a/include/linux/mm_types.h b/include/linux/mm_types.h index 26a30c3566f0..c8d0a73d64c4 100644 --- a/include/linux/mm_types.h +++ b/include/linux/mm_types.h @@ -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, }; diff --git a/include/trace/events/tlb.h b/include/trace/events/tlb.h index 4250f364a6ca..bc8815f45f3b 100644 --- a/include/trace/events/tlb.h +++ b/include/trace/events/tlb.h @@ -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 -- 2.20.1