From: Michael Jeanson <mjeanson@efficios.com>
To: Florian Weimer <fweimer@redhat.com>, libc-alpha@sourceware.org
Subject: Re: [PATCH v3] linux: Use rseq area unconditionally in sched_getcpu (bug 31479)
Date: Wed, 13 Mar 2024 16:51:15 -0400 [thread overview]
Message-ID: <adf21fcb-9174-45d2-96b5-5792b331efa6@efficios.com> (raw)
In-Reply-To: <87y1amnd85.fsf@oldenburg.str.redhat.com>
On 2024-03-13 15:28, Florian Weimer wrote:
> Originally, nptl/descr.h included <sys/rseq.h>, but we removed that
> in commit 2c6b4b272e6b4d07303af25709051c3e96288f2d ("nptl:
> Unconditionally use a 32-byte rseq area"). After that, it was
> not ensured that the RSEQ_SIG macro was defined during sched_getcpu.c
> compilation that provided a definition. This commit always checks
> the rseq area for CPU number information before using the other
> approaches.
>
> This adds an unnecessary (but well-predictable) branch on
> architectures which do not define RSEQ_SIG, but its cost is small
> compared to the system call. Most architectures that have vDSO
> acceleration for getcpu also have rseq support.
>
> Fixes: 2c6b4b272e6b4d07303af25709051c3e96288f2d
> Fixes: 1d350aa06091211863e41169729cee1bca39f72f
Would adding back the '#include <sys/rseq.h>' in nptl/descr.h have any adverse
consequences?
It would restore the original behavior without any effect on architectures
which do not define RSEQ_SIG.
next prev parent reply other threads:[~2024-03-13 20:51 UTC|newest]
Thread overview: 4+ messages / expand[flat|nested] mbox.gz Atom feed top
2024-03-13 19:28 [PATCH v3] linux: Use rseq area unconditionally in sched_getcpu (bug 31479) Florian Weimer
2024-03-13 20:51 ` Michael Jeanson [this message]
2024-03-13 20:52 ` Michael Jeanson
2024-03-15 14:40 ` Arjun Shankar
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