perf/x86/amd/uncore: Use hrtimer for handling overflows

Uncore counters do not provide mechanisms like interrupts to report
overflows and the accumulated user-visible count is incorrect if there
is more than one overflow between two successive read requests for the
same event because the value of prev_count goes out-of-date for
calculating the correct delta.

To avoid this, start a hrtimer to periodically initiate a pmu->read() of
the active counters for keeping prev_count up-to-date. It should be
noted that the hrtimer duration should be lesser than the shortest time
it takes for a counter to overflow for this approach to be effective.

Signed-off-by: Sandipan Das <sandipan.das@amd.com>
Signed-off-by: Ingo Molnar <mingo@kernel.org>
Acked-by: Peter Zijlstra <peterz@infradead.org>
Link: https://lore.kernel.org/r/8ecf5fe20452da1cd19cf3ff4954d3e7c5137468.1744906694.git.sandipan.das@amd.com

diff --git a/arch/x86/events/amd/uncore.c b/arch/x86/events/amd/uncore.c
index 010024f09f2c49853d0c71461d99853ac78e60fc..e09bfbb4a4cdf32ef6e916d279fa32e451386217 100644 (file)
--- a/arch/x86/events/amd/uncore.c
+++ b/arch/x86/events/amd/uncore.c
@@ -21,6 +21,7 @@
 #define NUM_COUNTERS_NB                4
 #define NUM_COUNTERS_L2                4
 #define NUM_COUNTERS_L3                6
+#define NUM_COUNTERS_MAX       64
 
 #define RDPMC_BASE_NB          6
 #define RDPMC_BASE_LLC         10
@@ -38,6 +39,10 @@ struct amd_uncore_ctx {
        int refcnt;
        int cpu;
        struct perf_event **events;
+       unsigned long active_mask[BITS_TO_LONGS(NUM_COUNTERS_MAX)];
+       int nr_active;
+       struct hrtimer hrtimer;
+       u64 hrtimer_duration;
 };
 
 struct amd_uncore_pmu {
@@ -87,6 +92,42 @@ static struct amd_uncore_pmu *event_to_amd_uncore_pmu(struct perf_event *event)
        return container_of(event->pmu, struct amd_uncore_pmu, pmu);
 }
 
+static enum hrtimer_restart amd_uncore_hrtimer(struct hrtimer *hrtimer)
+{
+       struct amd_uncore_ctx *ctx;
+       struct perf_event *event;
+       int bit;
+
+       ctx = container_of(hrtimer, struct amd_uncore_ctx, hrtimer);
+
+       if (!ctx->nr_active || ctx->cpu != smp_processor_id())
+               return HRTIMER_NORESTART;
+
+       for_each_set_bit(bit, ctx->active_mask, NUM_COUNTERS_MAX) {
+               event = ctx->events[bit];
+               event->pmu->read(event);
+       }
+
+       hrtimer_forward_now(hrtimer, ns_to_ktime(ctx->hrtimer_duration));
+       return HRTIMER_RESTART;
+}
+
+static void amd_uncore_start_hrtimer(struct amd_uncore_ctx *ctx)
+{
+       hrtimer_start(&ctx->hrtimer, ns_to_ktime(ctx->hrtimer_duration),
+                     HRTIMER_MODE_REL_PINNED_HARD);
+}
+
+static void amd_uncore_cancel_hrtimer(struct amd_uncore_ctx *ctx)
+{
+       hrtimer_cancel(&ctx->hrtimer);
+}
+
+static void amd_uncore_init_hrtimer(struct amd_uncore_ctx *ctx)
+{
+       hrtimer_setup(&ctx->hrtimer, amd_uncore_hrtimer, CLOCK_MONOTONIC, HRTIMER_MODE_REL_HARD);
+}
+
 static void amd_uncore_read(struct perf_event *event)
 {
        struct hw_perf_event *hwc = &event->hw;
@@ -117,18 +158,26 @@ static void amd_uncore_read(struct perf_event *event)
 
 static void amd_uncore_start(struct perf_event *event, int flags)
 {
+       struct amd_uncore_pmu *pmu = event_to_amd_uncore_pmu(event);
+       struct amd_uncore_ctx *ctx = *per_cpu_ptr(pmu->ctx, event->cpu);
        struct hw_perf_event *hwc = &event->hw;
 
+       if (!ctx->nr_active++)
+               amd_uncore_start_hrtimer(ctx);
+
        if (flags & PERF_EF_RELOAD)
                wrmsrl(hwc->event_base, (u64)local64_read(&hwc->prev_count));
 
        hwc->state = 0;
+       __set_bit(hwc->idx, ctx->active_mask);
        wrmsrl(hwc->config_base, (hwc->config | ARCH_PERFMON_EVENTSEL_ENABLE));
        perf_event_update_userpage(event);
 }
 
 static void amd_uncore_stop(struct perf_event *event, int flags)
 {
+       struct amd_uncore_pmu *pmu = event_to_amd_uncore_pmu(event);
+       struct amd_uncore_ctx *ctx = *per_cpu_ptr(pmu->ctx, event->cpu);
        struct hw_perf_event *hwc = &event->hw;
 
        wrmsrl(hwc->config_base, hwc->config);
@@ -138,6 +187,11 @@ static void amd_uncore_stop(struct perf_event *event, int flags)
                event->pmu->read(event);
                hwc->state |= PERF_HES_UPTODATE;
        }
+
+       if (!--ctx->nr_active)
+               amd_uncore_cancel_hrtimer(ctx);
+
+       __clear_bit(hwc->idx, ctx->active_mask);
 }
 
 static int amd_uncore_add(struct perf_event *event, int flags)
@@ -490,6 +544,9 @@ static int amd_uncore_ctx_init(struct amd_uncore *uncore, unsigned int cpu)
                                goto fail;
                        }
 
+                       amd_uncore_init_hrtimer(curr);
+                       curr->hrtimer_duration = 60LL * NSEC_PER_SEC;
+
                        cpumask_set_cpu(cpu, &pmu->active_mask);
                }
 
@@ -879,12 +936,18 @@ static int amd_uncore_umc_event_init(struct perf_event *event)
 
 static void amd_uncore_umc_start(struct perf_event *event, int flags)
 {
+       struct amd_uncore_pmu *pmu = event_to_amd_uncore_pmu(event);
+       struct amd_uncore_ctx *ctx = *per_cpu_ptr(pmu->ctx, event->cpu);
        struct hw_perf_event *hwc = &event->hw;
 
+       if (!ctx->nr_active++)
+               amd_uncore_start_hrtimer(ctx);
+
        if (flags & PERF_EF_RELOAD)
                wrmsrl(hwc->event_base, (u64)local64_read(&hwc->prev_count));
 
        hwc->state = 0;
+       __set_bit(hwc->idx, ctx->active_mask);
        wrmsrl(hwc->config_base, (hwc->config | AMD64_PERFMON_V2_ENABLE_UMC));
        perf_event_update_userpage(event);
 }