linux-kernel - Re: [PATCH] perf events: Add stalled cycles generic event

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: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Message-ID: <20110427162711.GA29460@elte.hu>
Date:	Wed, 27 Apr 2011 18:27:11 +0200
From:	Ingo Molnar <mingo@...e.hu>
To:	Arun Sharma <arun@...rma-home.net>
Cc:	Arun Sharma <asharma@...com>,
	Stephane Eranian <eranian@...gle.com>,
	Arnaldo Carvalho de Melo <acme@...radead.org>,
	linux-kernel@...r.kernel.org, Andi Kleen <ak@...ux.intel.com>,
	Peter Zijlstra <peterz@...radead.org>,
	Lin Ming <ming.m.lin@...el.com>,
	Arnaldo Carvalho de Melo <acme@...hat.com>,
	Thomas Gleixner <tglx@...utronix.de>,
	Peter Zijlstra <a.p.zijlstra@...llo.nl>, eranian@...il.com,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	Andrew Morton <akpm@...ux-foundation.org>
Subject: Re: [PATCH] perf events: Add stalled cycles generic event -
 PERF_COUNT_HW_STALLED_CYCLES


* Ingo Molnar <mingo@...e.hu> wrote:

> > [...] why not pick cycles where no uops are retiring?
> > 
> > cycles_no_uops_retired = cycles - c["UOPS_RETIRED:ANY:c=1:t=1"]
> >
> > In the presence of C-states and some halted cycles, I found that I couldn't 
> > measure it via UOPS_RETIRED:ANY:c=1:i=1 because it counts halted cycles too 
> > and could be greater than (unhalted) cycles.
> 
> Agreed, good point.
> 
> You are right that it is more robust to pick 'the CPU was busy on our behalf' 
> metric instead of a 'CPU is idle' metric, because that way 'HLT' as a special 
> type of idling around does not have to be identified.

Sidenote, there's one advantage of the idle event: it's more meaningful to 
profile idle cycles - and it's easy to ignore the HLT loop in the profile 
output (we already do).

That way we get a 'hidden overhead' profile: a profile of frequently executed 
code which executes in the CPU in a suboptimal way.

So we should probably offer both events.

Thanks,

	Ingo
--
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/