linux-kernel - Re: [PATCH] perf tools: rework of handling lack of sched

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Date:	Tue, 19 May 2015 17:16:28 +0200
From:	Petr Holasek <pholasek@...hat.com>
To:	Arnaldo Carvalho de Melo <acme@...nel.org>
Cc:	linux-kernel@...r.kernel.org, Ingo Molnar <mingo@...hat.com>,
	Jiri Olsa <jolsa@...hat.com>
Subject: Re: [PATCH] perf tools: rework of handling lack of sched_getcpu in
 old glibc

On Tue, 19 May 2015, Arnaldo Carvalho de Melo <acme@...nel.org> wrote:
> Em Tue, May 19, 2015 at 03:20:47PM +0200, Petr Holasek escreveu:
> > Commit e1e455f4f4d3 ("perf tools: Work around lack of sched_getcpu in
> > glibc < 2.6.") introduced weak function sched_getcpu() which should
> > be overridden by sched_getcpu() provided by glibc >= 2.6. Unfortunately,
> > the weak function was linked to sched_getcpu() used in perf bench numa
> > and made the benchmark heavily relying on this function unusable.
> > 
> > This patch alternates weak function magic for preprocessor defines.
> 
> With this you break the build again on RHEL5, right? That "fix" was a
> quickie, the good thing would be to have this sched_getcpu() thing
> somewhere else, far from its user, i.e. cloexec has no business doing
> this if there are other places (perf bench numa) that need this, right?
> 
> - Arnaldo
> 

This fix is also quickie, since perf bench numa was unusable from 4.0-rc1
and I needed to fix it somehow. But I agree, the right place for the fix
should be *far* from its users.

>  
> > Signed-off-by: Petr Holasek <pholasek@...hat.com>
> > ---
> >  tools/perf/util/cloexec.c | 13 +++++++++++--
> >  tools/perf/util/cloexec.h |  6 ------
> >  2 files changed, 11 insertions(+), 8 deletions(-)
> > 
> > diff --git a/tools/perf/util/cloexec.c b/tools/perf/util/cloexec.c
> > index 85b5238..23b8aa9 100644
> > --- a/tools/perf/util/cloexec.c
> > +++ b/tools/perf/util/cloexec.c
> > @@ -7,11 +7,20 @@
> >  
> >  static unsigned long flag = PERF_FLAG_FD_CLOEXEC;
> >  
> > -int __weak sched_getcpu(void)
> > +#ifdef __GLIBC_PREREQ
> > +#if !__GLIBC_PREREQ(2, 6)
> > +static int do_sched_getcpu(void)
> >  {
> >  	errno = ENOSYS;
> >  	return -1;
> >  }
> > +#else
> > +static int do_sched_getcpu(void)
> > +{
> > +	return sched_getcpu();
> > +}
> > +#endif
> > +#endif
> >  
> >  static int perf_flag_probe(void)
> >  {
> > @@ -27,7 +36,7 @@ static int perf_flag_probe(void)
> >  	pid_t pid = -1;
> >  	char sbuf[STRERR_BUFSIZE];
> >  
> > -	cpu = sched_getcpu();
> > +	cpu = do_sched_getcpu();
> >  	if (cpu < 0)
> >  		cpu = 0;
> >  
> > diff --git a/tools/perf/util/cloexec.h b/tools/perf/util/cloexec.h
> > index 68888c2..94a5a7d 100644
> > --- a/tools/perf/util/cloexec.h
> > +++ b/tools/perf/util/cloexec.h
> > @@ -3,10 +3,4 @@
> >  
> >  unsigned long perf_event_open_cloexec_flag(void);
> >  
> > -#ifdef __GLIBC_PREREQ
> > -#if !__GLIBC_PREREQ(2, 6)
> > -extern int sched_getcpu(void) __THROW;
> > -#endif
> > -#endif
> > -
> >  #endif /* __PERF_CLOEXEC_H */
> > -- 
> > 2.1.0

-- 
Petr Holasek
pholasek@...hat.com
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