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b=40duJJud9nPU258QdUTu6rPpihNacONjarUlwrvV4ozXaRNYI7CIAtMADLpczUrat32yqh5Fd5wNSU+aTjfhs68yPY2qunCZv+sh8Q3M98IDIDwh4oDwxzCBC+C6H1ek76vb4Dlwyn6gMmyemwg1pbVBk7o/e88f98OpsamDsNs= Authentication-Results: dkim=none (message not signed) header.d=none;dmarc=none action=none header.from=amd.com; Received: from PH7PR12MB5712.namprd12.prod.outlook.com (2603:10b6:510:1e3::13) by SN7PR12MB6742.namprd12.prod.outlook.com (2603:10b6:806:26e::11) with Microsoft SMTP Server (version=TLS1_2, cipher=TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384) id 15.20.8606.29; Thu, 10 Apr 2025 08:40:22 +0000 Received: from PH7PR12MB5712.namprd12.prod.outlook.com ([fe80::2efc:dc9f:3ba8:3291]) by PH7PR12MB5712.namprd12.prod.outlook.com ([fe80::2efc:dc9f:3ba8:3291%6]) with mapi id 15.20.8632.021; Thu, 10 Apr 2025 08:40:22 +0000 Message-ID: <083586a9-8717-4cc5-aab1-a7f40e6e8621@amd.com> Date: Thu, 10 Apr 2025 14:10:11 +0530 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH 2/4] perf/x86/amd/uncore: Use hrtimer for handling overflows To: Peter Zijlstra Cc: linux-perf-users@vger.kernel.org, linux-kernel@vger.kernel.org, mingo@redhat.com, acme@kernel.org, namhyung@kernel.org, mark.rutland@arm.com, alexander.shishkin@linux.intel.com, jolsa@kernel.org, irogers@google.com, adrian.hunter@intel.com, kan.liang@linux.intel.com, tglx@linutronix.de, bp@alien8.de, dave.hansen@linux.intel.com, x86@kernel.org, hpa@zytor.com, eranian@google.com, songliubraving@meta.com, ravi.bangoria@amd.com, ananth.narayan@amd.com References: <20250410082041.GY9833@noisy.programming.kicks-ass.net> Content-Language: en-US From: Sandipan Das In-Reply-To: <20250410082041.GY9833@noisy.programming.kicks-ass.net> Content-Type: text/plain; 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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 >> --- >> arch/x86/events/amd/uncore.c | 72 ++++++++++++++++++++++++++++++++++++ >> 1 file changed, 72 insertions(+) >> >> diff --git a/arch/x86/events/amd/uncore.c b/arch/x86/events/amd/uncore.c >> index 010024f09f2c..ee6528f2189f 100644 >> --- 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 +92,51 @@ 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; >> + unsigned long flags; >> + int bit; >> + >> + ctx = container_of(hrtimer, struct amd_uncore_ctx, hrtimer); >> + >> + if (!ctx->nr_active || ctx->cpu != smp_processor_id()) >> + return HRTIMER_NORESTART; >> + >> + /* >> + * Disable local interrupts to prevent pmu->start() or pmu->stop() >> + * from interrupting the update process >> + */ >> + local_irq_save(flags); >> + >> + for_each_set_bit(bit, ctx->active_mask, NUM_COUNTERS_MAX) { >> + event = ctx->events[bit]; >> + event->pmu->read(event); >> + } >> + >> + local_irq_restore(flags); >> + >> + 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); >> +} > > So I know you copied this from the Intel uncore driver; but would not > both be improved by using HRTIMER_MODE_HARD? > > It makes no sense to me to bounce the thing to SoftIRQ only to then > disable IRQs in the handler again. Not to mention that the whole SoftIRQ > things delays things further, giving more room/time to reach overflow > wrap. Agreed. Will address this in v2 for both the drivers.