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Tue, 3 Jun 2025 12:45:22 GMT Received: from smtpav04.dal12v.mail.ibm.com (unknown [127.0.0.1]) by IMSVA (Postfix) with ESMTP id 1D5BA5805E; Tue, 3 Jun 2025 12:45:22 +0000 (GMT) Received: from smtpav04.dal12v.mail.ibm.com (unknown [127.0.0.1]) by IMSVA (Postfix) with ESMTP id 2022A58052; Tue, 3 Jun 2025 12:45:18 +0000 (GMT) Received: from [9.61.248.228] (unknown [9.61.248.228]) by smtpav04.dal12v.mail.ibm.com (Postfix) with ESMTP; Tue, 3 Jun 2025 12:45:17 +0000 (GMT) Message-ID: <8e8f51d8-af64-4d9e-934b-c0ee9f131293@linux.ibm.com> Date: Tue, 3 Jun 2025 18:15:16 +0530 Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH V2] perf: Fix the throttle error of some clock events To: kan.liang@linux.intel.com, 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, Athira Rajeev , Madhavan Srinivasan Cc: eranian@google.com, ctshao@google.com, tmricht@linux.ibm.com, leo.yan@arm.com, Aishwarya TCV References: <20250528175832.2999139-1-kan.liang@linux.intel.com> Content-Language: en-GB From: Venkat Rao Bagalkote In-Reply-To: <20250528175832.2999139-1-kan.liang@linux.intel.com> Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 8bit X-TM-AS-GCONF: 00 X-Proofpoint-GUID: wyXliENgdp2QtoF2R1PL3Sa3uY9peLpc X-Proofpoint-Spam-Details-Enc: AW1haW4tMjUwNjAzMDEwOSBTYWx0ZWRfX8TXD4jvfA4++ D0y/ZXk99erNTDSxVkxJZD7aCVBmolNKr98ezndg18v5RftIJsBC0mtmF+pZ5hINDNYoSm99b+t am4YMjPIGu6Uf+UKis5YCv8wq1HwdBZnHcOIRfqgUzQ+dYh1rJCPea5z7z4oF+p+i2ToEt8iscW yeXqdH+GpqnOgcJH+P5lbxFditQZp2w2EY4sDCEaq0KXwJZPrYV6KBbebBYXDO38BGAnTQWeD43 8EHkwkTvPgIxA9+EuPrithRfySO2k876vPSkp+wTkhXG0/JbzvdoBSlaNHj9DyEPbO5vgDwVZNz XzWLljzksSX1DchhnUtwjCy6YnQbtnmG8t3uRJQd4EDp4Xem6m7Gsz+oQEamsNwdBPsLW25PJwC lf9PWoehoAmirIvfbSLn2IN8tPiKjbv3dLH2AdKQsNXINfo9AF7cyfWNn5ncTNZRkZcNl6RY X-Proofpoint-ORIG-GUID: Ak6jrcKSPN8OTB08XFQouZ6p0dAYbvDi X-Authority-Analysis: v=2.4 cv=c+WrQQ9l c=1 sm=1 tr=0 ts=683eee69 cx=c_pps a=AfN7/Ok6k8XGzOShvHwTGQ==:117 a=AfN7/Ok6k8XGzOShvHwTGQ==:17 a=IkcTkHD0fZMA:10 a=6IFa9wvqVegA:10 a=VwQbUJbxAAAA:8 a=7CQSdrXTAAAA:8 a=QyXUC8HyAAAA:8 a=VnNF1IyMAAAA:8 a=KJf0t8lbo5Kj145lKHwA:9 a=3ZKOabzyN94A:10 a=QEXdDO2ut3YA:10 a=a-qgeE7W1pNrGK8U0ZQC:22 X-Proofpoint-Virus-Version: vendor=baseguard engine=ICAP:2.0.293,Aquarius:18.0.1099,Hydra:6.0.736,FMLib:17.12.80.40 definitions=2025-06-03_01,2025-06-02_01,2025-03-28_01 X-Proofpoint-Spam-Details: rule=outbound_notspam policy=outbound score=0 mlxscore=0 spamscore=0 priorityscore=1501 mlxlogscore=999 phishscore=0 adultscore=0 clxscore=1011 lowpriorityscore=0 malwarescore=0 suspectscore=0 bulkscore=0 impostorscore=0 classifier=spam authscore=0 authtc=n/a authcc= route=outbound adjust=0 reason=mlx scancount=1 engine=8.19.0-2505280000 definitions=main-2506030109 On 28/05/25 11:28 pm, kan.liang@linux.intel.com wrote: > From: Kan Liang > > The Arm CI reports RCU stall, which can be reproduced by the below perf > command. > perf record -a -e cpu-clock -- sleep 2 This issue is reported on IBM CI as well. But the issue is hit, while running perf test (specifically while running  76: perf list tests) > > The cpu-clock and task_clock are two special SW events, which rely on > the hrtimer. Instead of invoking the stop(), the HRTIMER_NORESTART is > returned to stop the timer. Because the hrtimer interrupt handler cannot > cancel itself, which causes infinite loop. > > There may be two ways to fix it. > - Add a check of MAX_INTERRUPTS in the event_stop. Return immediately if > the stop is invoked by the throttle. > - Introduce a PMU flag to track the case. Avoid the event_stop in > perf_event_throttle() if the flag is detected. > > The latter looks more generic. It may be used if there are more other > cases that want to avoid the stop later. The latter is implemented. Tested this patch by applying on the linux-mainline kernel on IBM Power9 system, and it fixes the issue. Hence, Tested-by: Venkat Rao Bagalkote Regards, Venkat. > > Reported-by: Leo Yan > Reported-by: Aishwarya TCV > Closes: https://lore.kernel.org/lkml/20250527161656.GJ2566836@e132581.arm.com/ > Tested-by: Leo Yan > Signed-off-by: Kan Liang > --- > > Changes since V1: > - Rebase on top of the latest tip.git > - Add Tested-by from Leo > > include/linux/perf_event.h | 1 + > kernel/events/core.c | 23 ++++++++++++++++++++--- > 2 files changed, 21 insertions(+), 3 deletions(-) > > diff --git a/include/linux/perf_event.h b/include/linux/perf_event.h > index 52dc7cfab0e0..97a747a97a50 100644 > --- a/include/linux/perf_event.h > +++ b/include/linux/perf_event.h > @@ -305,6 +305,7 @@ struct perf_event_pmu_context; > #define PERF_PMU_CAP_EXTENDED_HW_TYPE 0x0100 > #define PERF_PMU_CAP_AUX_PAUSE 0x0200 > #define PERF_PMU_CAP_AUX_PREFER_LARGE 0x0400 > +#define PERF_PMU_CAP_NO_THROTTLE_STOP 0x0800 > > /** > * pmu::scope > diff --git a/kernel/events/core.c b/kernel/events/core.c > index f34c99f8ce8f..abd19bb571e3 100644 > --- a/kernel/events/core.c > +++ b/kernel/events/core.c > @@ -2656,7 +2656,22 @@ 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); > + /* > + * Some PMUs, e.g., cpu-clock and task_clock, may rely on > + * a special mechanism (hrtimer) to manipulate counters. > + * The regular stop doesn't work, since the hrtimer interrupt > + * handler cannot cancel itself. > + * > + * The stop should be avoided for such cases. Let the > + * driver-specific code handle it. > + * > + * The counters will eventually be disabled in the driver-specific > + * code. In unthrottle, they still need to be re-enabled. > + * There is no handling for PERF_PMU_CAP_NO_THROTTLE_STOP in > + * the perf_event_unthrottle(). > + */ > + if (!(event->pmu->capabilities & PERF_PMU_CAP_NO_THROTTLE_STOP)) > + event->pmu->stop(event, 0); > event->hw.interrupts = MAX_INTERRUPTS; > if (event == event->group_leader) > perf_log_throttle(event, 0); > @@ -11848,7 +11863,8 @@ static int cpu_clock_event_init(struct perf_event *event) > static struct pmu perf_cpu_clock = { > .task_ctx_nr = perf_sw_context, > > - .capabilities = PERF_PMU_CAP_NO_NMI, > + .capabilities = PERF_PMU_CAP_NO_NMI | > + PERF_PMU_CAP_NO_THROTTLE_STOP, > .dev = PMU_NULL_DEV, > > .event_init = cpu_clock_event_init, > @@ -11930,7 +11946,8 @@ static int task_clock_event_init(struct perf_event *event) > static struct pmu perf_task_clock = { > .task_ctx_nr = perf_sw_context, > > - .capabilities = PERF_PMU_CAP_NO_NMI, > + .capabilities = PERF_PMU_CAP_NO_NMI | > + PERF_PMU_CAP_NO_THROTTLE_STOP, > .dev = PMU_NULL_DEV, > > .event_init = task_clock_event_init,