From mboxrd@z Thu Jan 1 00:00:00 1970 From: kajoljain Subject: Re: [PATCH] perf/core: Fix hung issue on perf stat command during cpu hotplug Date: Wed, 2 Sep 2020 21:27:54 +0530 Message-ID: <42e61c14-4774-600d-2347-2cf2f8b2a59e@linux.ibm.com> References: <20200827064732.20860-1-kjain@linux.ibm.com> <20200902150516.GA3474644@kernel.org> Mime-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Transfer-Encoding: 7bit Return-path: In-Reply-To: <20200902150516.GA3474644@kernel.org> Content-Language: en-US Sender: linux-kernel-owner@vger.kernel.org To: Arnaldo Carvalho de Melo , Peter Zijlstra Cc: jolsa@redhat.com, linux-kernel@vger.kernel.org, linux-perf-users@vger.kernel.org, maddy@linux.ibm.com, mingo@redhat.com, mark.rutland@arm.com, alexander.shishkin@linux.intel.com, namhyung@kernel.org, daniel@iogearbox.net, brho@google.com, srikar@linux.vnet.ibm.com List-Id: linux-perf-users.vger.kernel.org On 9/2/20 8:35 PM, Arnaldo Carvalho de Melo wrote: > Em Thu, Aug 27, 2020 at 12:17:32PM +0530, Kajol Jain escreveu: >> Commit 2ed6edd33a21 ("perf: Add cond_resched() to task_function_call()") >> added assignment of ret value as -EAGAIN in case function >> call to 'smp_call_function_single' fails. >> For non-zero ret value, it did >> 'ret = !ret ? data.ret : -EAGAIN;', which always >> assign -EAGAIN to ret and make second if condition useless. >> >> In scenarios like when executing a perf stat with --per-thread option, and >> if any of the monitoring cpu goes offline, the 'smp_call_function_single' >> function could return -ENXIO, and with the above check, >> task_function_call hung and increases CPU >> usage (because of repeated 'smp_call_function_single()') >> >> Recration scenario: >> # perf stat -a --per-thread && (offline a CPU ) >> >> Patch here removes the tertiary condition added as part of that >> commit and added a check for NULL and -EAGAIN. > > I reproduced this issue with v5.9-rc3, now have to reboot for a conf > call, will try to test the patch afterwards, > > [65108.467416] IRQ 165: no longer affine to CPU23 > [65108.468495] smpboot: CPU 23 is now offline > [65129.003879] Uhhuh. NMI received for unknown reason 1c on CPU 20. > [65129.003880] Do you have a strange power saving mode enabled? > [65129.003880] Dazed and confused, but trying to continue > [65156.155539] Uhhuh. NMI received for unknown reason 1c on CPU 2. > [65156.155539] Do you have a strange power saving mode enabled? > [65156.155540] Dazed and confused, but trying to continue > [65161.985284] Uhhuh. NMI received for unknown reason 1c on CPU 21. > [65161.985285] Do you have a strange power saving mode enabled? > [65161.985285] Dazed and confused, but trying to continue > [65183.154444] Uhhuh. NMI received for unknown reason 1c on CPU 1. > [65183.154445] Do you have a strange power saving mode enabled? > [65183.154446] Dazed and confused, but trying to continue > [65189.724797] Uhhuh. NMI received for unknown reason 0c on CPU 4. > [65189.724798] Do you have a strange power saving mode enabled? > [65189.724799] Dazed and confused, but trying to continue > [65196.259918] Uhhuh. NMI received for unknown reason 1c on CPU 11. > [65196.259918] Do you have a strange power saving mode enabled? > [65196.259918] Dazed and confused, but trying to continue > [65234.794490] Uhhuh. NMI received for unknown reason 0c on CPU 5. > [65234.794491] Do you have a strange power saving mode enabled? > [65234.794491] Dazed and confused, but trying to continue > [65454.559831] Uhhuh. NMI received for unknown reason 1c on CPU 19. > [65454.559832] Do you have a strange power saving mode enabled? > [65454.559832] Dazed and confused, but trying to continue > [65529.657789] Uhhuh. NMI received for unknown reason 1c on CPU 3. > [65529.657790] Do you have a strange power saving mode enabled? > [65529.657790] Dazed and confused, but trying to continue > [acme@five perf]$ > > > Things seems to be working again after bringing that CPU back online: Hi Arnaldo, You are right, once we bring back the CPU again, things will start working as our 'smp_call_function_single' will not fail and we will come out of the loop. But till then, task_function_call will be hung. Thanks, Kajol Jain > > [root@five ~]# perf top --stdio -C 0-22 > Error: > The sys_perf_event_open() syscall returned with 16 (Device or resource busy) for event (cycles). > /bin/dmesg | grep -i perf may provide additional information. > > [root@five ~]# perf stat -e cycles sleep 1 > Error: > The sys_perf_event_open() syscall returned with 16 (Device or resource busy) for event (cycles). > /bin/dmesg | grep -i perf may provide additional information. > > [root@five ~]# perf record -e cycles sleep 1 > Error: > The sys_perf_event_open() syscall returned with 16 (Device or resource busy) for event (cycles). > /bin/dmesg | grep -i perf may provide additional information. > > [root@five ~]# echo 1 > /sys/devices/system/cpu/cpu23/online > [root@five ~]# perf record -e cycles sleep 1 > [ perf record: Woken up 1 times to write data ] > [ perf record: Captured and wrote 0.039 MB perf.data (7 samples) ] > [root@five ~]# perf stat -e cycles sleep 1 > > Performance counter stats for 'sleep 1': > > 842,743 cycles > > 1.000903853 seconds time elapsed > > 0.000902000 seconds user > 0.000000000 seconds sys > > > [root@five ~]# perf stat -e cycles sleep 1 > > > - Arnaldo > > >> Fixes: 2ed6edd33a21("perf: Add cond_resched() to task_function_call()") >> Signed-off-by: Kajol Jain >> Reported-by: Srikar Dronamraju >> Reviewed-by: Barret Rhoden >> Tested-by: Srikar Dronamraju >> --- >> kernel/events/core.c | 5 +++-- >> 1 file changed, 3 insertions(+), 2 deletions(-) >> >> Changelog: >> - Remove RFC tag >> - Resolve some nits issues like space after if and >> added -ENXIO in comment msg of function 'task_function_call' >> as suggested by Barret Rhoden. >> >> Link to the RFC: https://lkml.org/lkml/2020/8/26/896 >> >> diff --git a/kernel/events/core.c b/kernel/events/core.c >> index 5bfe8e3c6e44..cef646084198 100644 >> --- a/kernel/events/core.c >> +++ b/kernel/events/core.c >> @@ -99,7 +99,7 @@ static void remote_function(void *data) >> * retry due to any failures in smp_call_function_single(), such as if the >> * task_cpu() goes offline concurrently. >> * >> - * returns @func return value or -ESRCH when the process isn't running >> + * returns @func return value or -ESRCH or -ENXIO when the process isn't running >> */ >> static int >> task_function_call(struct task_struct *p, remote_function_f func, void *info) >> @@ -115,7 +115,8 @@ task_function_call(struct task_struct *p, remote_function_f func, void *info) >> for (;;) { >> ret = smp_call_function_single(task_cpu(p), remote_function, >> &data, 1); >> - ret = !ret ? data.ret : -EAGAIN; >> + if (!ret) >> + ret = data.ret; >> >> if (ret != -EAGAIN) >> break; >> -- >> 2.26.2 >> >