linux-kernel - Re: [PATCH] perf tools: Work around lack of sched

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Message-ID: <20150318091527.GM23123@twins.programming.kicks-ass.net>
Date:	Wed, 18 Mar 2015 10:15:27 +0100
From:	Peter Zijlstra <peterz@...radead.org>
To:	Vinson Lee <vlee@...pensource.com>
Cc:	Paul Mackerras <paulus@...ba.org>, Ingo Molnar <mingo@...hat.com>,
	Arnaldo Carvalho de Melo <acme@...nel.org>,
	Jiri Olsa <jolsa@...hat.com>,
	Adrian Hunter <adrian.hunter@...el.com>,
	Masami Hiramatsu <masami.hiramatsu.pt@...achi.com>,
	Namhyung Kim <namhyung@...nel.org>,
	LKML <linux-kernel@...r.kernel.org>,
	linux-perf-users@...r.kernel.org, Vinson Lee <vlee@...tter.com>,
	Yann Droneaud <ydroneaud@...eya.com>
Subject: Re: [PATCH] perf tools: Work around lack of sched_getcpu in glibc <
 2.6.

On Tue, Mar 17, 2015 at 04:49:13PM -0700, Vinson Lee wrote:
> On Mon, Feb 16, 2015 at 12:50 PM, Yann Droneaud <ydroneaud@...eya.com> wrote:
> >> +#ifdef __GLIBC_PREREQ
> >> +#if __GLIBC_PREREQ(2, 6)
> >> +#define HAVE_SCHED_GETCPU
> >> +#endif
> >> +#endif

> >> @@ -21,9 +27,13 @@ static int perf_flag_probe(void)
> >>       pid_t pid = -1;
> >>       char sbuf[STRERR_BUFSIZE];
> >>
> >> +#ifdef HAVE_SCHED_GETCPU
> >>       cpu = sched_getcpu();
> >>       if (cpu < 0)
> >>               cpu = 0;
> >> +#else
> >> +     cpu = 0;
> >> +#endif
> >>
> >>       while (1) {
> >>               /* check cloexec flag */

Would it not be much nicer to implement a sched_getcpu() stub that
returns -1 and sets errno to -ENOSYS or something?

That avoids the magic #ifdef mushroom.
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