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    SubjectRe: [RFC PATCH v3 00/16] Core scheduling v3
    On Wed, Aug 28, 2019 at 5:14 AM Matthew Garrett <mjg59@srcf.ucam.org> wrote:
    >
    > Apple have provided a sysctl that allows applications to indicate that
    > specific threads should make use of core isolation while allowing
    > the rest of the system to make use of SMT, and browsers (Safari, Firefox
    > and Chrome, at least) are now making use of this. Trying to do something
    > similar using cgroups seems a bit awkward. Would something like this be
    > reasonable? Having spoken to the Chrome team, I believe that the
    > semantics we want are:
    >
    > 1) A thread to be able to indicate that it should not run on the same
    > core as anything not in posession of the same cookie
    > 2) Descendents of that thread to (by default) have the same cookie
    > 3) No other thread be able to obtain the same cookie
    > 4) Threads not be able to rejoin the global group (ie, threads can
    > segregate themselves from their parent and peers, but can never rejoin
    > that group once segregated)
    >
    > but don't know if that's what everyone else would want.
    >
    > diff --git a/include/uapi/linux/prctl.h b/include/uapi/linux/prctl.h
    > index 094bb03b9cc2..5d411246d4d5 100644
    > --- a/include/uapi/linux/prctl.h
    > +++ b/include/uapi/linux/prctl.h
    > @@ -229,4 +229,5 @@ struct prctl_mm_map {
    > # define PR_PAC_APDBKEY (1UL << 3)
    > # define PR_PAC_APGAKEY (1UL << 4)
    >
    > +#define PR_CORE_ISOLATE 55
    > #endif /* _LINUX_PRCTL_H */
    > diff --git a/kernel/sys.c b/kernel/sys.c
    > index 12df0e5434b8..a054cfcca511 100644
    > --- a/kernel/sys.c
    > +++ b/kernel/sys.c
    > @@ -2486,6 +2486,13 @@ SYSCALL_DEFINE5(prctl, int, option, unsigned long, arg2, unsigned long, arg3,
    > return -EINVAL;
    > error = PAC_RESET_KEYS(me, arg2);
    > break;
    > + case PR_CORE_ISOLATE:
    > +#ifdef CONFIG_SCHED_CORE
    > + current->core_cookie = (unsigned long)current;

    Because AVX512 instructions could pull down the core frequency,
    we also want to give a magic cookie number to all AVX512-using
    tasks on the system, so they won't affect the performance/latency
    of any other tasks.

    This could be done by putting all AVX512 tasks into a cgroup, or
    by AVX512 detection the following patch introduced.

    https://git.kernel.org/pub/scm/linux/kernel/git/tip/tip.git/commit/?id=2f7726f955572e587d5f50fbe9b2deed5334bd90

    Thanks,
    -Aubrey

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