From af3bdb991a5cb57c189d34aadbd3aa88995e0d9f Mon Sep 17 00:00:00 2001 From: Andi Kleen Date: Wed, 8 Aug 2018 00:12:07 -0700 Subject: perf/x86/intel: Add a separate Arch Perfmon v4 PMI handler Implements counter freezing for Arch Perfmon v4 (Skylake and newer). This allows to speed up the PMI handler by avoiding unnecessary MSR writes and make it more accurate. The Arch Perfmon v4 PMI handler is substantially different than the older PMI handler. Differences to the old handler: - It relies on counter freezing, which eliminates several MSR writes from the PMI handler and lowers the overhead significantly. It makes the PMI handler more accurate, as all counters get frozen atomically as soon as any counter overflows. So there is much less counting of the PMI handler itself. With the freezing we don't need to disable or enable counters or PEBS. Only BTS which does not support auto-freezing still needs to be explicitly managed. - The PMU acking is done at the end, not the beginning. This makes it possible to avoid manual enabling/disabling of the PMU, instead we just rely on the freezing/acking. - The APIC is acked before reenabling the PMU, which avoids problems with LBRs occasionally not getting unfreezed on Skylake. - Looping is only needed to workaround a corner case which several PMIs are very close to each other. For common cases, the counters are freezed during PMI handler. It doesn't need to do re-check. This patch: - Adds code to enable v4 counter freezing - Fork <=v3 and >=v4 PMI handlers into separate functions. - Add kernel parameter to disable counter freezing. It took some time to debug counter freezing, so in case there are new problems we added an option to turn it off. Would not expect this to be used until there are new bugs. - Only for big core. The patch for small core will be posted later separately. Performance: When profiling a kernel build on Kabylake with different perf options, measuring the length of all NMI handlers using the nmi handler trace point: V3 is without counter freezing. V4 is with counter freezing. The value is the average cost of the PMI handler. (lower is better) perf options ` V3(ns) V4(ns) delta -c 100000 1088 894 -18% -g -c 100000 1862 1646 -12% --call-graph lbr -c 100000 3649 3367 -8% --c.g. dwarf -c 100000 2248 1982 -12% Signed-off-by: Andi Kleen Signed-off-by: Kan Liang Signed-off-by: Peter Zijlstra (Intel) Cc: Alexander Shishkin Cc: Arnaldo Carvalho de Melo Cc: Jiri Olsa Cc: Linus Torvalds Cc: Peter Zijlstra Cc: Stephane Eranian Cc: Thomas Gleixner Cc: Vince Weaver Cc: acme@kernel.org Link: http://lkml.kernel.org/r/1533712328-2834-2-git-send-email-kan.liang@linux.intel.com Signed-off-by: Ingo Molnar --- Documentation/admin-guide/kernel-parameters.txt | 5 +++++ 1 file changed, 5 insertions(+) (limited to 'Documentation/admin-guide/kernel-parameters.txt') diff --git a/Documentation/admin-guide/kernel-parameters.txt b/Documentation/admin-guide/kernel-parameters.txt index 92eb1f42240d..6795dedcbd1e 100644 --- a/Documentation/admin-guide/kernel-parameters.txt +++ b/Documentation/admin-guide/kernel-parameters.txt @@ -856,6 +856,11 @@ causing system reset or hang due to sending INIT from AP to BSP. + disable_counter_freezing [HW] + Disable Intel PMU counter freezing feature. + The feature only exists starting from + Arch Perfmon v4 (Skylake and newer). + disable_ddw [PPC/PSERIES] Disable Dynamic DMA Window support. Use this if to workaround buggy firmware. -- cgit v1.2.3