Re: [PATCH V13 - RESEND 09/10] arm64/perf: Implement branch records save on task sched out
From: Rajnesh Kanwal <hidden>
Date: 2023-08-02 11:59:38
Also in:
linux-perf-users, lkml
quoted hunk ↗ jump to hunk
diff --git a/drivers/perf/arm_brbe.c b/drivers/perf/arm_brbe.c index 203cd4f350d5..2177632befa6 100644 --- a/drivers/perf/arm_brbe.c +++ b/drivers/perf/arm_brbe.c@@ -165,6 +165,36 @@ static int stitch_stored_live_entries(struct brbe_regset *stored,return min(nr_live + nr_stored, nr_max); } +static int brbe_branch_save(struct brbe_regset *live, int nr_hw_entries) +{ + u64 brbfcr = read_sysreg_s(SYS_BRBFCR_EL1); + int nr_live; + + write_sysreg_s(brbfcr | BRBFCR_EL1_PAUSED, SYS_BRBFCR_EL1); + isb(); + + nr_live = capture_brbe_regset(live, nr_hw_entries); + + write_sysreg_s(brbfcr & ~BRBFCR_EL1_PAUSED, SYS_BRBFCR_EL1); + isb(); + + return nr_live; +} + +void armv8pmu_branch_save(struct arm_pmu *arm_pmu, void *ctx) +{ + struct arm64_perf_task_context *task_ctx = ctx; + struct brbe_regset live[BRBE_MAX_ENTRIES]; + int nr_live, nr_store, nr_hw_entries; + + nr_hw_entries = brbe_get_numrec(arm_pmu->reg_brbidr); + nr_live = brbe_branch_save(live, nr_hw_entries); + nr_store = task_ctx->nr_brbe_records; + nr_store = stitch_stored_live_entries(task_ctx->store, live, nr_store, + nr_live, nr_hw_entries); + task_ctx->nr_brbe_records = nr_store; +}
Asking out-of-curiosity. Have you thought about virtualization use case. Current LBR implementation create an event for the guest and save/restore happens using the sched_task callback. (Correct me if I am wrong). Given you are only saving and processing those saved entries, how do you plan to expose the entries to the guest? Thanks Rajnesh
quoted hunk ↗ jump to hunk
+ /* * Generic perf branch filters supported on BRBE *diff --git a/drivers/perf/arm_pmuv3.c b/drivers/perf/arm_pmuv3.c index 408974d5c57b..aa3c7b3dcdd6 100644 --- a/drivers/perf/arm_pmuv3.c +++ b/drivers/perf/arm_pmuv3.c@@ -923,9 +923,19 @@ static int armv8pmu_user_event_idx(struct perf_event *event)static void armv8pmu_sched_task(struct perf_event_pmu_context *pmu_ctx, bool sched_in) { struct arm_pmu *armpmu = to_arm_pmu(pmu_ctx->pmu); + void *task_ctx = pmu_ctx ? pmu_ctx->task_ctx_data : NULL; - if (sched_in && armpmu->has_branch_stack) - armv8pmu_branch_reset(); + if (armpmu->has_branch_stack) { + /* Save branch records in task_ctx on sched out */ + if (task_ctx && !sched_in) { + armv8pmu_branch_save(armpmu, task_ctx); + return; + } + + /* Reset branch records on sched in */ + if (sched_in) + armv8pmu_branch_reset(); + } }
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