linux-kernel - Re: [PATCH 2/5] glibc: sched_getcpu(): use rseq cpu

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Message-ID: <c9c53d4b-ed9b-f2d9-60b0-e5e805de0324@arm.com>
Date:   Thu, 18 Apr 2019 15:33:33 +0000
From:   Szabolcs Nagy <Szabolcs.Nagy@....com>
To:     Mathieu Desnoyers <mathieu.desnoyers@...icios.com>,
        Carlos O'Donell <carlos@...hat.com>
CC:     nd <nd@....com>, Florian Weimer <fweimer@...hat.com>,
        Joseph Myers <joseph@...esourcery.com>,
        "libc-alpha@...rceware.org" <libc-alpha@...rceware.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        Ben Maurer <bmaurer@...com>,
        Peter Zijlstra <peterz@...radead.org>,
        "Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>,
        Boqun Feng <boqun.feng@...il.com>,
        Will Deacon <Will.Deacon@....com>,
        Dave Watson <davejwatson@...com>, Paul Turner <pjt@...gle.com>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "linux-api@...r.kernel.org" <linux-api@...r.kernel.org>
Subject: Re: [PATCH 2/5] glibc: sched_getcpu(): use rseq cpu_id TLS on Linux
 (v2)

On 16/04/2019 18:32, Mathieu Desnoyers wrote:
> --- a/sysdeps/unix/sysv/linux/sched_getcpu.c
> +++ b/sysdeps/unix/sysv/linux/sched_getcpu.c
> @@ -37,3 +37,26 @@ sched_getcpu (void)
>    return -1;
>  #endif
>  }
> +
> +#ifdef __NR_rseq
> +#include <sys/rseq.h>
> +#endif
> +
> +#if defined __NR_rseq && defined RSEQ_SIG
> +extern __attribute__ ((tls_model ("initial-exec")))
> +__thread volatile struct rseq __rseq_abi;

i'd expect sys/rseq.h to provide this declaration.

> +
> +int
> +sched_getcpu (void)
> +{
> +  int cpu_id = __rseq_abi.cpu_id;
> +
> +  return cpu_id >= 0 ? cpu_id : vsyscall_sched_getcpu ();
> +}
> +#else
> +int
> +sched_getcpu (void)
> +{
> +  return vsyscall_sched_getcpu ();
> +}
> +#endif
> -- 2.17.1
>