diff options
Diffstat (limited to 'arch/x86/events/intel/lbr.c')
| -rw-r--r-- | arch/x86/events/intel/lbr.c | 70 |
1 files changed, 32 insertions, 38 deletions
diff --git a/arch/x86/events/intel/lbr.c b/arch/x86/events/intel/lbr.c index 707d358e0dff..fc6cf21c535e 100644 --- a/arch/x86/events/intel/lbr.c +++ b/arch/x86/events/intel/lbr.c @@ -380,7 +380,6 @@ static void __intel_pmu_lbr_save(struct x86_perf_task_context *task_ctx) void intel_pmu_lbr_sched_task(struct perf_event_context *ctx, bool sched_in) { - struct cpu_hw_events *cpuc = this_cpu_ptr(&cpu_hw_events); struct x86_perf_task_context *task_ctx; /* @@ -390,31 +389,21 @@ void intel_pmu_lbr_sched_task(struct perf_event_context *ctx, bool sched_in) */ task_ctx = ctx ? ctx->task_ctx_data : NULL; if (task_ctx) { - if (sched_in) { + if (sched_in) __intel_pmu_lbr_restore(task_ctx); - cpuc->lbr_context = ctx; - } else { + else __intel_pmu_lbr_save(task_ctx); - } return; } /* - * When sampling the branck stack in system-wide, it may be - * necessary to flush the stack on context switch. This happens - * when the branch stack does not tag its entries with the pid - * of the current task. Otherwise it becomes impossible to - * associate a branch entry with a task. This ambiguity is more - * likely to appear when the branch stack supports priv level - * filtering and the user sets it to monitor only at the user - * level (which could be a useful measurement in system-wide - * mode). In that case, the risk is high of having a branch - * stack with branch from multiple tasks. - */ - if (sched_in) { + * Since a context switch can flip the address space and LBR entries + * are not tagged with an identifier, we need to wipe the LBR, even for + * per-cpu events. You simply cannot resolve the branches from the old + * address space. + */ + if (sched_in) intel_pmu_lbr_reset(); - cpuc->lbr_context = ctx; - } } static inline bool branch_user_callstack(unsigned br_sel) @@ -422,7 +411,7 @@ static inline bool branch_user_callstack(unsigned br_sel) return (br_sel & X86_BR_USER) && (br_sel & X86_BR_CALL_STACK); } -void intel_pmu_lbr_enable(struct perf_event *event) +void intel_pmu_lbr_add(struct perf_event *event) { struct cpu_hw_events *cpuc = this_cpu_ptr(&cpu_hw_events); struct x86_perf_task_context *task_ctx; @@ -430,27 +419,38 @@ void intel_pmu_lbr_enable(struct perf_event *event) if (!x86_pmu.lbr_nr) return; - /* - * Reset the LBR stack if we changed task context to - * avoid data leaks. - */ - if (event->ctx->task && cpuc->lbr_context != event->ctx) { - intel_pmu_lbr_reset(); - cpuc->lbr_context = event->ctx; - } cpuc->br_sel = event->hw.branch_reg.reg; - if (branch_user_callstack(cpuc->br_sel) && event->ctx && - event->ctx->task_ctx_data) { + if (branch_user_callstack(cpuc->br_sel) && event->ctx->task_ctx_data) { task_ctx = event->ctx->task_ctx_data; task_ctx->lbr_callstack_users++; } - cpuc->lbr_users++; + /* + * Request pmu::sched_task() callback, which will fire inside the + * regular perf event scheduling, so that call will: + * + * - restore or wipe; when LBR-callstack, + * - wipe; otherwise, + * + * when this is from __perf_event_task_sched_in(). + * + * However, if this is from perf_install_in_context(), no such callback + * will follow and we'll need to reset the LBR here if this is the + * first LBR event. + * + * The problem is, we cannot tell these cases apart... but we can + * exclude the biggest chunk of cases by looking at + * event->total_time_running. An event that has accrued runtime cannot + * be 'new'. Conversely, a new event can get installed through the + * context switch path for the first time. + */ perf_sched_cb_inc(event->ctx->pmu); + if (!cpuc->lbr_users++ && !event->total_time_running) + intel_pmu_lbr_reset(); } -void intel_pmu_lbr_disable(struct perf_event *event) +void intel_pmu_lbr_del(struct perf_event *event) { struct cpu_hw_events *cpuc = this_cpu_ptr(&cpu_hw_events); struct x86_perf_task_context *task_ctx; @@ -467,12 +467,6 @@ void intel_pmu_lbr_disable(struct perf_event *event) cpuc->lbr_users--; WARN_ON_ONCE(cpuc->lbr_users < 0); perf_sched_cb_dec(event->ctx->pmu); - - if (cpuc->enabled && !cpuc->lbr_users) { - __intel_pmu_lbr_disable(); - /* avoid stale pointer */ - cpuc->lbr_context = NULL; - } } void intel_pmu_lbr_enable_all(bool pmi) |