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Date: Wed, 26 Apr 2023 10:23:35 -0400
From: "Liang, Kan" <kan.liang@...ux.intel.com>
To: Peter Zijlstra <peterz@...radead.org>
Cc: mingo@...hat.com, linux-kernel@...r.kernel.org, eranian@...gle.com,
ak@...ux.intel.com
Subject: Re: [PATCH V4 1/2] perf/x86/intel/ds: Flush the PEBS buffer in PEBS
enable
On 2023-04-26 9:18 a.m., Peter Zijlstra wrote:
> On Fri, Apr 21, 2023 at 11:45:28AM -0700, kan.liang@...ux.intel.com wrote:
>> From: Kan Liang <kan.liang@...ux.intel.com>
>>
>> Several similar kernel warnings can be triggered,
>>
>> [56605.607840] CPU0 PEBS record size 0, expected 32, config 0
>> cpuc->record_size=208
>>
>> when the below commands are running in parallel for a while on SPR.
>>
>> while true; do perf record --no-buildid -a --intr-regs=AX -e
>> cpu/event=0xd0,umask=0x81/pp -c 10003 -o /dev/null ./triad; done &
>>
>> while true; do perf record -o /tmp/out -W -d -e
>> '{ld_blocks.store_forward:period=1000000,
>> MEM_TRANS_RETIRED.LOAD_LATENCY:u:precise=2:ldlat=4}'
>> -c 1037 ./triad; done
>> *The triad program is just the generation of loads/stores.
>>
>> The warnings are triggered when an unexpected PEBS record (with a
>> different config and size) is found.
>>
>> A system-wide PEBS event with the large PEBS config may be enabled
>> during a context switch. Some PEBS records for the system-wide PEBS may
>> be generated while the old task is sched out but the new one hasn't been
>> sched in yet. When the new task is sched in, the cpuc->pebs_record_size
>> may be updated for the per-task PEBS events. So the existing system-wide
>> PEBS records have a different size from the later PEBS records.
>>
>> The PEBS buffer should be flushed right before the hardware is
>> reprogrammed. The new size and threshold should be updated after the old
>> buffer has been flushed.
>>
>> Reported-by: Stephane Eranian <eranian@...gle.com>
>> Suggested-by: Peter Zijlstra (Intel) <peterz@...radead.org>
>> Signed-off-by: Kan Liang <kan.liang@...ux.intel.com>
>> ---
>
> So I find it much easier to read the whole thing when collapsed.
> Something like the below; that ok with you?
Yes, the changes look good to me.
Thanks,
Kan
>
> ---
> arch/x86/events/intel/ds.c | 56 ++++++++++++++++++++++-----------------
> arch/x86/include/asm/perf_event.h | 3 +++
> 2 files changed, 35 insertions(+), 24 deletions(-)
>
> diff --git a/arch/x86/events/intel/ds.c b/arch/x86/events/intel/ds.c
> index a2e566e53076..df88576d6b2a 100644
> --- a/arch/x86/events/intel/ds.c
> +++ b/arch/x86/events/intel/ds.c
> @@ -1229,12 +1229,14 @@ pebs_update_state(bool needed_cb, struct cpu_hw_events *cpuc,
> struct perf_event *event, bool add)
> {
> struct pmu *pmu = event->pmu;
> +
> /*
> * Make sure we get updated with the first PEBS
> * event. It will trigger also during removal, but
> * that does not hurt:
> */
> - bool update = cpuc->n_pebs == 1;
> + if (cpuc->n_pebs == 1)
> + cpuc->pebs_data_cfg = PEBS_UPDATE_DS_SW;
>
> if (needed_cb != pebs_needs_sched_cb(cpuc)) {
> if (!needed_cb)
> @@ -1242,7 +1244,7 @@ pebs_update_state(bool needed_cb, struct cpu_hw_events *cpuc,
> else
> perf_sched_cb_dec(pmu);
>
> - update = true;
> + cpuc->pebs_data_cfg |= PEBS_UPDATE_DS_SW;
> }
>
> /*
> @@ -1252,24 +1254,13 @@ pebs_update_state(bool needed_cb, struct cpu_hw_events *cpuc,
> if (x86_pmu.intel_cap.pebs_baseline && add) {
> u64 pebs_data_cfg;
>
> - /* Clear pebs_data_cfg and pebs_record_size for first PEBS. */
> - if (cpuc->n_pebs == 1) {
> - cpuc->pebs_data_cfg = 0;
> - cpuc->pebs_record_size = sizeof(struct pebs_basic);
> - }
> -
> pebs_data_cfg = pebs_update_adaptive_cfg(event);
> -
> - /* Update pebs_record_size if new event requires more data. */
> - if (pebs_data_cfg & ~cpuc->pebs_data_cfg) {
> - cpuc->pebs_data_cfg |= pebs_data_cfg;
> - adaptive_pebs_record_size_update();
> - update = true;
> - }
> + /*
> + * Be sure to update the thresholds when we change the record.
> + */
> + if (pebs_data_cfg & ~cpuc->pebs_data_cfg)
> + cpuc->pebs_data_cfg |= pebs_data_cfg | PEBS_UPDATE_DS_SW;
> }
> -
> - if (update)
> - pebs_update_threshold(cpuc);
> }
>
> void intel_pmu_pebs_add(struct perf_event *event)
> @@ -1326,9 +1317,17 @@ static void intel_pmu_pebs_via_pt_enable(struct perf_event *event)
> wrmsrl(base + idx, value);
> }
>
> +static inline void intel_pmu_drain_large_pebs(struct cpu_hw_events *cpuc)
> +{
> + if (cpuc->n_pebs == cpuc->n_large_pebs &&
> + cpuc->n_pebs != cpuc->n_pebs_via_pt)
> + intel_pmu_drain_pebs_buffer();
> +}
> +
> void intel_pmu_pebs_enable(struct perf_event *event)
> {
> struct cpu_hw_events *cpuc = this_cpu_ptr(&cpu_hw_events);
> + u64 pebs_data_cfg = cpuc->pebs_data_cfg & ~PEBS_UPDATE_DS_SW;
> struct hw_perf_event *hwc = &event->hw;
> struct debug_store *ds = cpuc->ds;
> unsigned int idx = hwc->idx;
> @@ -1344,11 +1343,22 @@ void intel_pmu_pebs_enable(struct perf_event *event)
>
> if (x86_pmu.intel_cap.pebs_baseline) {
> hwc->config |= ICL_EVENTSEL_ADAPTIVE;
> - if (cpuc->pebs_data_cfg != cpuc->active_pebs_data_cfg) {
> - wrmsrl(MSR_PEBS_DATA_CFG, cpuc->pebs_data_cfg);
> - cpuc->active_pebs_data_cfg = cpuc->pebs_data_cfg;
> + if (pebs_data_cfg != cpuc->active_pebs_data_cfg) {
> + /*
> + * drain_pebs() assumes uniform record size;
> + * hence we need to drain when changing said
> + * size.
> + */
> + intel_pmu_drain_large_pebs(cpuc);
> + adaptive_pebs_record_size_update();
> + wrmsrl(MSR_PEBS_DATA_CFG, pebs_data_cfg);
> + cpuc->active_pebs_data_cfg = pebs_data_cfg;
> }
> }
> + if (cpuc->pebs_data_cfg & PEBS_UPDATE_DS_SW) {
> + cpuc->pebs_data_cfg = pebs_data_cfg;
> + pebs_update_threshold(cpuc);
> + }
>
> if (idx >= INTEL_PMC_IDX_FIXED) {
> if (x86_pmu.intel_cap.pebs_format < 5)
> @@ -1391,9 +1401,7 @@ void intel_pmu_pebs_disable(struct perf_event *event)
> struct cpu_hw_events *cpuc = this_cpu_ptr(&cpu_hw_events);
> struct hw_perf_event *hwc = &event->hw;
>
> - if (cpuc->n_pebs == cpuc->n_large_pebs &&
> - cpuc->n_pebs != cpuc->n_pebs_via_pt)
> - intel_pmu_drain_pebs_buffer();
> + intel_pmu_drain_large_pebs(cpuc);
>
> cpuc->pebs_enabled &= ~(1ULL << hwc->idx);
>
> diff --git a/arch/x86/include/asm/perf_event.h b/arch/x86/include/asm/perf_event.h
> index 8fc15ed5e60b..abf09882f58b 100644
> --- a/arch/x86/include/asm/perf_event.h
> +++ b/arch/x86/include/asm/perf_event.h
> @@ -121,6 +121,9 @@
> #define PEBS_DATACFG_LBRS BIT_ULL(3)
> #define PEBS_DATACFG_LBR_SHIFT 24
>
> +/* Steal the highest bit of pebs_data_cfg for SW usage */
> +#define PEBS_UPDATE_DS_SW BIT_ULL(63)
> +
> /*
> * Intel "Architectural Performance Monitoring" CPUID
> * detection/enumeration details:
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