From: Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
To: Florian Weimer <fweimer@redhat.com>
Cc: linux-kernel@vger.kernel.org, Ingo Molnar <mingo@redhat.com>,
Peter Zijlstra <peterz@infradead.org>,
libc-alpha@sourceware.org
Subject: Re: rseq CPU ID not correct on 6.0 kernels for pinned threads
Date: Thu, 12 Jan 2023 15:25:42 -0500 [thread overview]
Message-ID: <5c64b742-c41a-8c59-c0c8-8b4cdedaaba5@efficios.com> (raw)
In-Reply-To: <871qnzpv9l.fsf@oldenburg.str.redhat.com>
On 2023-01-12 11:33, Florian Weimer wrote:
> * Mathieu Desnoyers:
>
>> As you also point out, it can also be caused by some other task
>> modifying the affinity of your task concurrently. You could print
>> the result of sched_getaffinity on error to get a better idea of
>> the expected vs actual mask.
>>
>> Lastly, it could be caused by CPU hotplug which would set all bits
>> in the affinity mask as a fallback. As you mention it should not be
>> the cause there.
>>
>> Can you share your kernel configuration ?
>
> Attached.
>
> cpupower frequency-info says:
>
> analyzing CPU 0:
> driver: intel_cpufreq
> CPUs which run at the same hardware frequency: 0
> CPUs which need to have their frequency coordinated by software: 0
> maximum transition latency: 20.0 us
> hardware limits: 800 MHz - 4.60 GHz
> available cpufreq governors: conservative ondemand userspace powersave performance schedutil
> current policy: frequency should be within 800 MHz and 4.60 GHz.
> The governor "schedutil" may decide which speed to use
> within this range.
> current CPU frequency: Unable to call hardware
> current CPU frequency: 3.20 GHz (asserted by call to kernel)
> boost state support:
> Supported: yes
> Active: yes
>
> And I have: kernel.sched_energy_aware = 1
>
>> Is this on a physical machine or in a virtual machine ?
>
> I think it happened on both.
>
> I added additional error reporting to the test (running on kernel
> 6.0.18-300.fc37.x86_64), and it seems that there is something that is
> mucking with affinity masks:
>
> info: Detected CPU set size (in bits): 64
> info: Maximum test CPU: 19
> error: Pinned thread 17 ran on impossible cpu 7
> info: getcpu reported CPU 7, node 0
> info: CPU affinity mask: 0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19
> error: Pinned thread 3 ran on impossible cpu 13
> info: getcpu reported CPU 13, node 0
> info: CPU affinity mask: 0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19
> info: Main thread ran on 2 CPU(s) of 20 available CPU(s)
> info: Other threads ran on 20 CPU(s)
>
> For each of these threads, the affinity mask should be a singleton set.
> Now I need to find out if there is a process that changes affinity
> settings.
If it's not cpu hotunplug, then perhaps something like systemd modifies
the AllowedCPUs of your cpuset concurrently ?
Thanks,
Mathieu
--
Mathieu Desnoyers
EfficiOS Inc.
https://www.efficios.com
next prev parent reply other threads:[~2023-01-12 20:25 UTC|newest]
Thread overview: 8+ messages / expand[flat|nested] mbox.gz Atom feed top
2023-01-11 11:26 Florian Weimer
2023-01-11 14:52 ` Mathieu Desnoyers
2023-01-11 19:31 ` Mathieu Desnoyers
2023-01-11 21:51 ` Mathieu Desnoyers
2023-01-12 16:33 ` Florian Weimer
2023-01-12 20:25 ` Mathieu Desnoyers [this message]
2023-01-13 16:06 ` Florian Weimer
2023-01-13 16:13 ` Waiman Long
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