linux-kernel - Re: [PATCH v5 0/2] perf: use hrtimer for event multiplexing

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]

Date:	Fri, 22 Mar 2013 18:36:40 +0100
From:	Stephane Eranian <eranian@...gle.com>
To:	Andi Kleen <ak@...ux.intel.com>
Cc:	LKML <linux-kernel@...r.kernel.org>,
	Peter Zijlstra <peterz@...radead.org>,
	"mingo@...e.hu" <mingo@...e.hu>,
	Arnaldo Carvalho de Melo <acme@...hat.com>,
	Jiri Olsa <jolsa@...hat.com>,
	Namhyung Kim <namhyung.kim@....com>
Subject: Re: [PATCH v5 0/2] perf: use hrtimer for event multiplexing

On Fri, Mar 22, 2013 at 6:33 PM, Andi Kleen <ak@...ux.intel.com> wrote:
>
> On Fri, Mar 22, 2013 at 11:51:37AM +0100, Stephane Eranian wrote:
> > The current scheme of using the timer tick was fine
> > for per-thread events. However, it was causing
> > bias issues in system-wide mode (including for
> > uncore PMUs). Event groups would not get their
> > fair share of runtime on the PMU. With tickless
> > kernels, if a core is idle there is no timer tick,
> > and thus no event rotation (multiplexing). However,
> > there are events (especially uncore events) which do
> > count even though cores are asleep.
>
> Would it be possible to only do this when uncore events
> are active? Otherwise it may have a large power cost
> and actually change results, as the core counters
> will tick more.
>
the hrtimer is activated only when multiplexing is needed
and that's for any PMU.
--
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/