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[59.124.168.89]) by smtp.gmail.com with ESMTPSA id w5-20020a17090aea0500b002532ddc3a00sm7402441pjy.15.2023.06.27.02.03.46 (version=TLS1_2 cipher=ECDHE-ECDSA-CHACHA20-POLY1305 bits=256/256); Tue, 27 Jun 2023 02:03:49 -0700 (PDT) Date: Tue, 27 Jun 2023 17:03:44 +0800 From: Eric Lin To: Peter Zijlstra , Stephane Eranian Cc: mingo@redhat.com, acme@kernel.org, mark.rutland@arm.com, alexander.shishkin@linux.intel.com, jolsa@kernel.org, namhyung@kernel.org, irogers@google.com, adrian.hunter@intel.com, palmer@dabbelt.com, linux-perf-users@vger.kernel.org, linux-kernel@vger.kernel.org, linux-riscv@lists.infradead.org, greentime.hu@sifive.com, vincent.chen@sifive.com Subject: Re: [PATCH] perf/core: Add pmu stop before unthrottling to prevent WARNING Message-ID: <20230627090343.GA11571@hsinchu16> References: <20230602094841.1225-1-eric.lin@sifive.com> <20230621115811.GD2053369@hirez.programming.kicks-ass.net> MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline Content-Transfer-Encoding: 8bit In-Reply-To: <20230621115811.GD2053369@hirez.programming.kicks-ass.net> User-Agent: Mutt/1.9.4 (2018-02-28) Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Wed, Jun 21, 2023 at 01:58:11PM +0200, Peter Zijlstra wrote: > On Tue, Jun 20, 2023 at 11:18:05PM -0700, Stephane Eranian wrote: > > On Tue, Jun 20, 2023 at 9:25 PM Eric Lin wrote: > > > > > > CC: Stephane Eranian > > > > > > On Fri, Jun 2, 2023 at 5:49 PM Eric Lin wrote: > > > > > > > > Currently, during the perf sampling, if the perf interrupt takes too long, > > > > perf framework will lower the perf_event_max_sample_rate. This will limit > > > > the number of samples per timer tick (max_samples_per_tick) and set hwc->interrupts > > > > to MAX_INTERRUPTS within the __perf_event_account_interrupt() function. > > > > > > > > Afterward, the perf framework will unthrottle the event in the timer interrupt > > > > handler, which triggers the driver's *_pmu_start() function. Most of the driver's > > > > *_pmu_start() functions will check the event->hw.state to determine whether this > > > > event has stopped. If the event has not stopped, a WARN_ON_ONCE() warning > > > > will be triggered as shown below: > > > > > > > > [ 2110.224723] ------------[ cut here ]------------ > > > > [ 2110.224851] WARNING: CPU: 0 PID: 240 at drivers/perf/riscv_pmu.c:184 riscv_pmu_start+0x7c/0x8e > > > > [ 2110.225242] Modules linked in: > > > > [ 2110.225380] CPU: 0 PID: 240 Comm: ls Not tainted 6.4-rc4-g19d0788e9ef2 #1 > > > > [ 2110.225574] Hardware name: SiFive (DT) > > > > [ 2110.225657] epc : riscv_pmu_start+0x7c/0x8e > > > > [ 2110.225834] ra : riscv_pmu_start+0x28/0x8e > > > > [ 2110.225998] epc : ffffffff80aef864 ra : ffffffff80aef810 sp : ffff8f80004db6f0 > > > > [ 2110.226135] gp : ffffffff81c83750 tp : ffffaf80069f9bc0 t0 : ffff8f80004db6c0 > > > > [ 2110.226245] t1 : 0000000000000000 t2 : 000000000000001f s0 : ffff8f80004db720 > > > > [ 2110.226367] s1 : ffffaf8008ca1068 a0 : 0000ffffffffffff a1 : 0000000000000000 > > > > [ 2110.226488] a2 : 0000000000000001 a3 : 0000000000000870 a4 : 0000000000000000 > > > > [ 2110.226605] a5 : 0000000000000000 a6 : 0000000000000840 a7 : 0000000000000030 > > > > [ 2110.226721] s2 : 0000000000000000 s3 : ffffaf8005165800 s4 : ffffaf800424da00 > > > > [ 2110.226838] s5 : ffffffffffffffff s6 : ffffffff81cc7590 s7 : 0000000000000000 > > > > [ 2110.226955] s8 : 0000000000000006 s9 : 0000000000000001 s10: ffffaf807efbc340 > > > > [ 2110.227064] s11: ffffaf807efbbf00 t3 : ffffaf8006a16028 t4 : 00000000dbfbb796 > > > > [ 2110.227180] t5 : 0000000700000000 t6 : ffffaf8005269870 > > > > [ 2110.227277] status: 0000000200000100 badaddr: 0000000000000000 cause: 0000000000000003 > > > > [ 2110.227407] [] riscv_pmu_start+0x7c/0x8e > > > > [ 2110.227622] [] perf_adjust_freq_unthr_context+0x15e/0x174 > > > > [ 2110.227961] [] perf_event_task_tick+0x88/0x9c > > > > [ 2110.228235] [] scheduler_tick+0xfe/0x27c > > > > [ 2110.228463] [] update_process_times+0x9a/0xba > > > > [ 2110.228690] [] tick_sched_handle+0x32/0x66 > > > > [ 2110.229007] [] tick_sched_timer+0x64/0xb0 > > > > [ 2110.229253] [] __hrtimer_run_queues+0x156/0x2f4 > > > > [ 2110.229446] [] hrtimer_interrupt+0xe2/0x1fe > > > > [ 2110.229637] [] riscv_timer_interrupt+0x38/0x42 > > > > [ 2110.229984] [] handle_percpu_devid_irq+0x90/0x1d2 > > > > [ 2110.230162] [] generic_handle_domain_irq+0x28/0x36 > > > > > > > > To prevent this warning, we should call the driver's *_pmu_stop() function before unthrottling > > > > > > > > Signed-off-by: Eric Lin > > > > --- > > > > kernel/events/core.c | 1 + > > > > 1 file changed, 1 insertion(+) > > > > > > > > diff --git a/kernel/events/core.c b/kernel/events/core.c > > > > index db016e418931..098c875abe88 100644 > > > > --- a/kernel/events/core.c > > > > +++ b/kernel/events/core.c > > > > @@ -4128,6 +4128,7 @@ perf_adjust_freq_unthr_context(struct perf_event_context *ctx, bool unthrottle) > > > > > > > > if (hwc->interrupts == MAX_INTERRUPTS) { > > > > hwc->interrupts = 0; > > > > + event->pmu->stop(event, 0); > > > > But how could the event have been stopped with a call to pmu->stop() > > during throttling? > > Yeah, Changelog fails to explain how we got to the faulty state -- and > without that we can't judge if the proposed solution actually fixes the > problem or not. > Hi Stephane, Peter, Most of the pmu driver will call *_pmu_stop(event,0) in the *_pmu_handle_irq() function and update the hwc->state with PERF_HES_STOPPED flag as below: arch/alpha/kernel/perf_event.c:856: if (perf_event_overflow(event, &data, regs)) { arch/alpha/kernel/perf_event.c-857- /* Interrupts coming too quickly; "throttle" the arch/alpha/kernel/perf_event.c-858- * counter, i.e., disable it for a little while. arch/alpha/kernel/perf_event.c-859- */ arch/alpha/kernel/perf_event.c-860- alpha_pmu_stop(event, 0); arch/alpha/kernel/perf_event.c-861- } ----- arch/arc/kernel/perf_event.c:603: if (perf_event_overflow(event, &data, regs)) arch/arc/kernel/perf_event.c-604- arc_pmu_stop(event, 0); arch/arc/kernel/perf_event.c-605- } ----- arch/x86/events/amd/core.c:935: if (perf_event_overflow(event, &data, regs)) arch/x86/events/amd/core.c-936- x86_pmu_stop(event, 0); arch/x86/events/amd/core.c-937- } ----- However, some of the pmu drivers stop the event in the *_pmu_handle_irq() without update the hwc->state with PERF_HES_STOPPED flag as below: arch/arm/kernel/perf_event_v7.c:994: if (perf_event_overflow(event, &data, regs)) arch/arm/kernel/perf_event_v7.c-995- cpu_pmu->disable(event); // <== not update with PERF_HES_STOPPED arch/arm/kernel/perf_event_v7.c-996- } ------ arch/csky/kernel/perf_event.c:1142: if (perf_event_overflow(event, &data, regs)) arch/csky/kernel/perf_event.c-1143- csky_pmu_stop_event(event); // <== not update with PERF_HES_STOPPED arch/csky/kernel/perf_event.c-1144- } ------- arch/loongarch/kernel/perf_event.c:492: if (perf_event_overflow(event, data, regs)) arch/loongarch/kernel/perf_event.c-493- loongarch_pmu_disable_event(idx); // <== not update with PERF_HES_STOPPED arch/loongarch/kernel/perf_event.c-494-} ------- arch/mips/kernel/perf_event_mipsxx.c:794: if (perf_event_overflow(event, data, regs)) arch/mips/kernel/perf_event_mipsxx.c-795- mipsxx_pmu_disable_event(idx); // <== not update with PERF_HES_STOPPED arch/mips/kernel/perf_event_mipsxx.c-796-} .... Furthermore, these drivers did not add event->hw.state checking in *_pmu_start() before starting the event like x86 does: 1497 static void x86_pmu_start(struct perf_event *event, int flags) 1498 { 1499 struct cpu_hw_events *cpuc = this_cpu_ptr(&cpu_hw_events); 1500 int idx = event->hw.idx; 1501 1502 if (WARN_ON_ONCE(!(event->hw.state & PERF_HES_STOPPED))) 1503 return; 1504 As a result, these drivers won't trigger the WARN_ON_ONCE warning as shown in this patch. However, if a pmu driver like RISC-V pmu which didn't call *_pmu_stop(event,0) without update the hwc->state with PERF_HES_STOPPED flag in the *_pmu_handle_irq() function but has event->hw.state checking in *_pmu_start(), it could trigger the WARN_ON_ONCE warning as shown in this patch. Therefore, I think we need to call pmu->stop() before unthrottling the event to prevent this warning. Or maybe we can add hwc->state checking before we call pmu->stop() as below: --- a/kernel/events/core.c +++ b/kernel/events/core.c @@ -4128,7 +4128,8 @@ perf_adjust_freq_unthr_context(struct perf_event_context *ctx, bool unthrottle) if (hwc->interrupts == MAX_INTERRUPTS) { hwc->interrupts = 0; - event->pmu->stop(event, 0); + if (!(hwc->state & PERF_HES_STOPPED)) + event->pmu->stop(event, 0); perf_log_throttle(event, 1); event->pmu->start(event, 0); } Thanks. Best Regards, Eric Lin. > > > > > > > perf_log_throttle(event, 1); > > > > event->pmu->start(event, 0); > > > > } > > > > -- > > > > 2.17.1 > > > >