Messages in this thread Patch in this message | | | Date | Wed, 11 May 2022 16:20:38 +0200 | From | Peter Zijlstra <> | Subject | [PATCH 1/5] perf/x86/amd: Fix AMD BRS period adjustment |
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There's two problems with the current amd_brs_adjust_period() code:
- it isn't in fact AMD specific and wil always adjust the period;
- it adjusts the period, while it should only adjust the event count, resulting in repoting a short period.
Fix this by using x86_pmu.limit_period, this makes it specific to the AMD BRS case and ensures only the event count is adjusted while the reported period is unmodified.
Fixes: ba2fe7500845 ("perf/x86/amd: Add AMD branch sampling period adjustment") Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org> --- arch/x86/events/amd/core.c | 13 +++++++++++++ arch/x86/events/core.c | 7 ------- arch/x86/events/perf_event.h | 18 ------------------ 3 files changed, 13 insertions(+), 25 deletions(-)
--- a/arch/x86/events/amd/core.c +++ b/arch/x86/events/amd/core.c @@ -1258,6 +1258,18 @@ static void amd_pmu_sched_task(struct pe amd_pmu_brs_sched_task(ctx, sched_in); } +static u64 amd_pmu_limit_period(struct perf_event *event, u64 left) +{ + /* + * Decrease period by the depth of the BRS feature to get the last N + * taken branches and approximate the desired period + */ + if (has_branch_stack(event) && left > x86_pmu.lbr_nr) + left -= x86_pmu.lbr_nr; + + return left; +} + static __initconst const struct x86_pmu amd_pmu = { .name = "AMD", .handle_irq = amd_pmu_handle_irq, @@ -1418,6 +1430,7 @@ static int __init amd_core_pmu_init(void if (boot_cpu_data.x86 >= 0x19 && !amd_brs_init()) { x86_pmu.get_event_constraints = amd_get_event_constraints_f19h; x86_pmu.sched_task = amd_pmu_sched_task; + x86_pmu.limit_period = amd_pmu_limit_period; /* * put_event_constraints callback same as Fam17h, set above */ --- a/arch/x86/events/core.c +++ b/arch/x86/events/core.c @@ -1375,13 +1375,6 @@ int x86_perf_event_set_period(struct per return x86_pmu.set_topdown_event_period(event); /* - * decrease period by the depth of the BRS feature to get - * the last N taken branches and approximate the desired period - */ - if (has_branch_stack(event)) - period = amd_brs_adjust_period(period); - - /* * If we are way outside a reasonable range then just skip forward: */ if (unlikely(left <= -period)) { --- a/arch/x86/events/perf_event.h +++ b/arch/x86/events/perf_event.h @@ -1254,14 +1254,6 @@ static inline void amd_pmu_brs_del(struc } void amd_pmu_brs_sched_task(struct perf_event_context *ctx, bool sched_in); - -static inline s64 amd_brs_adjust_period(s64 period) -{ - if (period > x86_pmu.lbr_nr) - return period - x86_pmu.lbr_nr; - - return period; -} #else static inline int amd_brs_init(void) { @@ -1290,11 +1282,6 @@ static inline void amd_pmu_brs_sched_tas { } -static inline s64 amd_brs_adjust_period(s64 period) -{ - return period; -} - static inline void amd_brs_enable_all(void) { } @@ -1324,11 +1311,6 @@ static inline void amd_brs_enable_all(vo static inline void amd_brs_disable_all(void) { } - -static inline s64 amd_brs_adjust_period(s64 period) -{ - return period; -} #endif /* CONFIG_CPU_SUP_AMD */ static inline int is_pebs_pt(struct perf_event *event)
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