From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from foss.arm.com (foss.arm.com [217.140.110.172]) by smtp.subspace.kernel.org (Postfix) with ESMTP id C726212E7E; Mon, 9 Jun 2025 12:34:24 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=217.140.110.172 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1749472467; cv=none; b=oUroPPE9BHsE27VrBlHwWyvmpXUqTjto14/XWNxvaPZNxTppgjmbxKxLxqa3NCQrlEbrMa+BN8mZ+s5aDBgzl+1YKVzm6+2kGhi0sPHOMZGo1JdEdZZWI0jl59lvUPumdeMGu89hi4vdEwdbZ1jqB861O0mGIg32HMQ9BmG7wz8= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1749472467; c=relaxed/simple; bh=HDFpx8Cc3xPi5mnpLaZZU6nEkfCGbZwZD/KbTCBU2dE=; h=Date:From:To:Cc:Subject:Message-ID:References:MIME-Version: Content-Type:Content-Disposition:In-Reply-To; b=AmhpYoHBtyOFOQX+nnqg0Yd1hiBU/x9xcl9DUHRetiZ2BTxcqrp9o7p39XKrPdGpAqo72QcYRPqe4V/Cgn2WCknFjfV8Tje8E680xGY/t4aIcstVQvqihJL8hXK0mpMqfpy12cok93QOX4hXYhTymOk7Vg8ShVE/b48mNiwv77c= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=arm.com; spf=pass smtp.mailfrom=arm.com; arc=none smtp.client-ip=217.140.110.172 Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=arm.com Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=arm.com Received: from usa-sjc-imap-foss1.foss.arm.com (unknown [10.121.207.14]) by usa-sjc-mx-foss1.foss.arm.com (Postfix) with ESMTP id E5D21150C; Mon, 9 Jun 2025 05:34:04 -0700 (PDT) Received: from localhost (e132581.arm.com [10.1.196.87]) by usa-sjc-imap-foss1.foss.arm.com (Postfix) with ESMTPSA id 6B7443F673; Mon, 9 Jun 2025 05:34:23 -0700 (PDT) Date: Mon, 9 Jun 2025 13:34:15 +0100 From: Leo Yan To: kan.liang@linux.intel.com Cc: peterz@infradead.org, mingo@redhat.com, namhyung@kernel.org, irogers@google.com, mark.rutland@arm.com, linux-kernel@vger.kernel.org, linux-perf-users@vger.kernel.org, eranian@google.com, ctshao@google.com, tmricht@linux.ibm.com, Aishwarya TCV , Alexei Starovoitov , Venkat Rao Bagalkote , Vince Weaver Subject: Re: [PATCH V4] perf: Fix the throttle error of some clock events Message-ID: <20250609123415.GJ8020@e132581.arm.com> References: <20250606192546.915765-1-kan.liang@linux.intel.com> Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20250606192546.915765-1-kan.liang@linux.intel.com> Hi Kan, On Fri, Jun 06, 2025 at 12:25:46PM -0700, kan.liang@linux.intel.com wrote: [...] > There may be two ways to fix it. > - Introduce a PMU flag to track the case. Avoid the event_stop in > perf_event_throttle() if the flag is detected. > It has been implemented in the > https://lore.kernel.org/lkml/20250528175832.2999139-1-kan.liang@linux.intel.com/ > The new flag was thought to be an overkill for the issue. > - Add a check in the event_stop. Return immediately if the throttle is > invoked in the hrtimer handler. Rely on the existing HRTIMER_NORESTART > method to stop the timer. > > The latter is implemented here. > > Move event->hw.interrupts = MAX_INTERRUPTS before the stop(). It makes > the order the same as perf_event_unthrottle(). Except the patch, no one > checks the hw.interrupts in the stop(). There is no impact from the > order change. > > When stops in the throttle, the event should not be updated, > stop(event, 0). I am confused for this conclusion. When a CPU or task clock event is stopped by throttling, should it also be updated? Otherwise, we will lose accouting for the period prior to the throttling. I saw you exchanged with Alexei for a soft lockup issue, the reply [1] shows that skipping event update on throttling does not help to resolve the lockup issue. Could you elaberate why we don't need to update clock events when throttling? Thanks, Leo [1] https://lore.kernel.org/linux-perf-users/CAADnVQKRJKsG08KkEriuBQop0LgDr+c9rkNE6MUh_n3rzZoXVQ@mail.gmail.com/ > But the cpu_clock_event_stop() doesn't handle the flag. > In logic, it's wrong. But it didn't bring any problems with the old > code, because the stop() was not invoked when handling the throttle. > Checking the flag before updating the event. > > Reported-by: Leo Yan > Reported-by: Aishwarya TCV > Closes: https://lore.kernel.org/lkml/20250527161656.GJ2566836@e132581.arm.com/ > Reported-by: Alexei Starovoitov > Closes: https://lore.kernel.org/lkml/djxlh5fx326gcenwrr52ry3pk4wxmugu4jccdjysza7tlc5fef@ktp4rffawgcw/ > Reported-by: Venkat Rao Bagalkote > Closes: https://lore.kernel.org/lkml/8e8f51d8-af64-4d9e-934b-c0ee9f131293@linux.ibm.com/ > Reported-by: Vince Weaver > Closes: https://lore.kernel.org/lkml/4ce106d0-950c-aadc-0b6a-f0215cd39913@maine.edu/ > Reviewed-by: Ian Rogers > Signed-off-by: Kan Liang > --- > > The patch is to fix the issue introduced by > > 9734e25fbf5a perf: Fix the throttle logic for a group > > It is still in the tip.git, I'm not sure if the commit ID is valid. So > the Fixes tag is not added. > > There are some discussions regarding to a soft lockup issue. > That is an existing issue, which are not introduced by the above change. > It should be fixed separately. > https://lore.kernel.org/lkml/CAADnVQ+Lx0HWEM8xdLC80wco3BTUPAD_2dQ-3oZFiECZMcw2aQ@mail.gmail.com/ > > Changes since V3: > - Check before update in event_stop() > - Add Reviewed-by from Ian > > kernel/events/core.c | 15 +++++++++++---- > 1 file changed, 11 insertions(+), 4 deletions(-) > > diff --git a/kernel/events/core.c b/kernel/events/core.c > index f34c99f8ce8f..cc77f127e11a 100644 > --- a/kernel/events/core.c > +++ b/kernel/events/core.c > @@ -2656,8 +2656,8 @@ static void perf_event_unthrottle(struct perf_event *event, bool start) > > static void perf_event_throttle(struct perf_event *event) > { > - event->pmu->stop(event, 0); > event->hw.interrupts = MAX_INTERRUPTS; > + event->pmu->stop(event, 0); > if (event == event->group_leader) > perf_log_throttle(event, 0); > } > @@ -11749,7 +11749,12 @@ static void perf_swevent_cancel_hrtimer(struct perf_event *event) > { > struct hw_perf_event *hwc = &event->hw; > > - if (is_sampling_event(event)) { > + /* > + * The throttle can be triggered in the hrtimer handler. > + * The HRTIMER_NORESTART should be used to stop the timer, > + * rather than hrtimer_cancel(). See perf_swevent_hrtimer() > + */ > + if (is_sampling_event(event) && (hwc->interrupts != MAX_INTERRUPTS)) { > ktime_t remaining = hrtimer_get_remaining(&hwc->hrtimer); > local64_set(&hwc->period_left, ktime_to_ns(remaining)); > > @@ -11804,7 +11809,8 @@ static void cpu_clock_event_start(struct perf_event *event, int flags) > static void cpu_clock_event_stop(struct perf_event *event, int flags) > { > perf_swevent_cancel_hrtimer(event); > - cpu_clock_event_update(event); > + if (flags & PERF_EF_UPDATE) > + cpu_clock_event_update(event); > } > > static int cpu_clock_event_add(struct perf_event *event, int flags) > @@ -11882,7 +11888,8 @@ static void task_clock_event_start(struct perf_event *event, int flags) > static void task_clock_event_stop(struct perf_event *event, int flags) > { > perf_swevent_cancel_hrtimer(event); > - task_clock_event_update(event, event->ctx->time); > + if (flags & PERF_EF_UPDATE) > + task_clock_event_update(event, event->ctx->time); > } > > static int task_clock_event_add(struct perf_event *event, int flags) > -- > 2.38.1 >