lists.openwall.net   lists  /  announce  owl-users  owl-dev  john-users  john-dev  passwdqc-users  yescrypt  popa3d-users  /  oss-security  kernel-hardening  musl  sabotage  tlsify  passwords  /  crypt-dev  xvendor  /  Bugtraq  Full-Disclosure  linux-kernel  linux-netdev  linux-ext4  linux-hardening  linux-cve-announce  PHC 
Open Source and information security mailing list archives
 
Hash Suite for Android: free password hash cracker in your pocket
[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]
Message-ID: <20140814184115.GS5803@tassilo.jf.intel.com>
Date:	Thu, 14 Aug 2014 11:41:15 -0700
From:	Andi Kleen <ak@...ux.intel.com>
To:	Stephane Eranian <eranian@...gle.com>
Cc:	Namhyung Kim <namhyung@...nel.org>, Jiri Olsa <jolsa@...hat.com>,
	Arnaldo Carvalho de Melo <acme@...radead.org>,
	Andi Kleen <andi@...stfloor.org>,
	Peter Zijlstra <peterz@...radead.org>,
	LKML <linux-kernel@...r.kernel.org>,
	Ingo Molnar <mingo@...nel.org>
Subject: Re: [PATCH 4/5] perf, x86: Add INST_RETIRED.ALL workarounds

On Thu, Aug 14, 2014 at 07:47:56PM +0200, Stephane Eranian wrote:
> [+perf tool maintainers]
> 
> On Thu, Aug 14, 2014 at 4:30 PM, Andi Kleen <ak@...ux.intel.com> wrote:
> >
> > I understand all your points, but there's no alternative.
> > The only other way would be to disable INST_RETIRED.ALL.
> >
> You cannot do that either. INST_RETIRED:ALL is important.
> I assume the bug applies whether or not the event is used
> with a filter.

> 
> I think we need to ensure that by looking at the perf.data file,
> one can reconstruct the total number of inst_Retired:all
> occurrences for the run. With a fixed period, one would do
> num_samples * fixed_period. I know the Gooda tool does
> that. It is used to estimate the number of events captured
> vs. the number of events occurring.

Is that really a problem?

Normally periods are not that small, especially not for 
instruction retired. I don't think you can run such
a small period on instruction retired for
any significant time without throttling.

With sensible periods, let's say >10k, the error from
losing a few bits is very small. It would surprise
me if you can actually measure it.

There will be always much more jitter just from standard
system noise.

-Andi
--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@...r.kernel.org
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/

Powered by blists - more mailing lists