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Re: [PATCH][BZ #15533] Avoid unnecessary slowdown from profiling with audit
- From: OndÅej BÃlka <neleai at seznam dot cz>
- To: Carlos O'Donell <carlos at redhat dot com>
- Cc: Alexander Monakov <amonakov at ispras dot ru>, GNU C Library <libc-alpha at sourceware dot org>
- Date: Wed, 5 Jun 2013 12:34:56 +0200
- Subject: Re: [PATCH][BZ #15533] Avoid unnecessary slowdown from profiling with audit
- References: <alpine dot LNX dot 2 dot 00 dot 1305250406320 dot 23866 at monopod dot intra dot ispras dot ru> <alpine dot LNX dot 2 dot 00 dot 1306041253320 dot 27183 at monopod dot intra dot ispras dot ru> <51AE14E3 dot 50007 at redhat dot com>
On Tue, Jun 04, 2013 at 12:25:07PM -0400, Carlos O'Donell wrote:
> On 06/04/2013 04:57 AM, Alexander Monakov wrote:
> > Ping? The previous discussion focused on copyright assignment matters.
> >
> > If this can go in, please commit.
> >
> > On Sat, 25 May 2013, Alexander Monakov wrote:
> >> Presently, using the rtld-audit interfaces introduces a slowdown due to
> >> enabling profiling instrumentation (as if LD_AUDIT implied LD_PROFILE).
> >> However, instrumenting is only necessary if one of audit libraries provides
> >> PLT hooks (la_plt{enter,exit} symbols). Otherwise, the slowdown can be
> >> avoided.
> >>
> >> In the synthetic test attached to the bugzilla issue, the slowdown is 19x. On
> >> another application I tested, the slowdown from profiling was 10%. The
> >> current behavior strongly discourages using the audit interface when
> >> compromising performance is not desired.
> >>
> >> The following patch adjusts the logic that enables profiling to iterate over
> >> all audit modules and check if any of those provides a PLT hook.
> >>
> >> I have an FSF copyright assignment as a GCC contributor (but I do not have
> >> commit access in glibc).
> >>
> >> Thanks.
> >>
>
> It's on the patch review list:
>
> http://sourceware.org/glibc/wiki/Pending%20Reviews
>
> We just haven't gotten to it, sorry :-(
>
Patch itself looks good, however I do not have big picture of rtld. Could
somebody else verify that only way for profiling are la_plt{enter,exit}
hooks?