From 1182a49529edde899be4b4f0e1ab76e626976eb6 Mon Sep 17 00:00:00 2001 From: Reinette Chatre Date: Wed, 19 Sep 2018 10:29:07 -0700 Subject: perf/x86: Add helper to obtain performance counter index perf_event_read_local() is the safest way to obtain measurements associated with performance events. In some cases the overhead introduced by perf_event_read_local() affects the measurements and the use of rdpmcl() is needed. rdpmcl() requires the index of the performance counter used so a helper is introduced to determine the index used by a provided performance event. The index used by a performance event may change when interrupts are enabled. A check is added to ensure that the index is only accessed with interrupts disabled. Even with this check the use of this counter needs to be done with care to ensure it is queried and used within the same disabled interrupts section. This change introduces a new checkpatch warning: CHECK: extern prototypes should be avoided in .h files +extern int x86_perf_rdpmc_index(struct perf_event *event); This warning was discussed and designated as a false positive in http://lkml.kernel.org/r/20180919091759.GZ24124@hirez.programming.kicks-ass.net Suggested-by: Peter Zijlstra Signed-off-by: Reinette Chatre Signed-off-by: Thomas Gleixner Acked-by: Peter Zijlstra (Intel) Cc: fenghua.yu@intel.com Cc: tony.luck@intel.com Cc: acme@kernel.org Cc: gavin.hindman@intel.com Cc: jithu.joseph@intel.com Cc: dave.hansen@intel.com Cc: hpa@zytor.com Link: https://lkml.kernel.org/r/b277ffa78a51254f5414f7b1bc1923826874566e.1537377064.git.reinette.chatre@intel.com --- arch/x86/include/asm/perf_event.h | 1 + 1 file changed, 1 insertion(+) (limited to 'arch/x86/include/asm/perf_event.h') diff --git a/arch/x86/include/asm/perf_event.h b/arch/x86/include/asm/perf_event.h index 12f54082f4c8..b2cf84c35a6d 100644 --- a/arch/x86/include/asm/perf_event.h +++ b/arch/x86/include/asm/perf_event.h @@ -270,6 +270,7 @@ struct perf_guest_switch_msr { extern struct perf_guest_switch_msr *perf_guest_get_msrs(int *nr); extern void perf_get_x86_pmu_capability(struct x86_pmu_capability *cap); extern void perf_check_microcode(void); +extern int x86_perf_rdpmc_index(struct perf_event *event); #else static inline struct perf_guest_switch_msr *perf_guest_get_msrs(int *nr) { -- cgit v1.2.3