linux-kernel - Re: [PATCH RFC V2 1/1] x86, perf: Add a freq pmu driver

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:	Thu, 23 Jul 2015 10:25:43 -0700
From:	Andi Kleen <ak@...ux.intel.com>
To:	Stephane Eranian <eranian@...gle.com>
Cc:	Peter Zijlstra <peterz@...radead.org>,
	Kan Liang <kan.liang@...el.com>,
	"mingo@...hat.com" <mingo@...hat.com>,
	Arnaldo Carvalho de Melo <acme@...nel.org>,
	Mark Rutland <mark.rutland@....com>,
	Adrian Hunter <adrian.hunter@...el.com>,
	David Ahern <dsahern@...il.com>, Jiri Olsa <jolsa@...nel.org>,
	Namhyung Kim <namhyung@...nel.org>,
	LKML <linux-kernel@...r.kernel.org>,
	Andy Lutomirski <luto@...nel.org>
Subject: Re: [PATCH RFC V2 1/1] x86, perf: Add a freq pmu driver

> I understand the value of the tsc and smi events. It is not
> clear to me what aperf/mperf buys you over cycles and ref-cycles:
> 
> $ perf stat -a -e msr/aperf/,msr/mperf/,cycles,ref-cycles -C 1 -I 1000 sleep 10
> #           time             counts unit events
>      2.000361718         14,826,353      msr/aperf/
>      2.000361718         11,865,170      msr/mperf/
>      2.000361718         17,170,101      cycles
>      2.000361718         13,629,675      ref-cycles
> 
> Only the ratio aperf/mperf is defined, here 1.25 and the ratio
> cycles/ref-cycles is 1.25 as well. So what is a situation where
> aperf/mperf provides better info than cycles/ref-cycles?
> The SDM also says aperf/mperf only defined when running in C0 mode.

aperf/mperf excludes idle and it accounts for throttling and p-state
coordination. So it's a indicator how busy the CPU is while running.
That's why it is used as input to the p-state algorithm.

cycles/ref-cycles is just the core busy indicator related
to idle. That's a different metric.

Also we have PPERF now on some parts (productive performance count), 
but it also needs a ratio, so MPERF is needed to get the ratio.

BTW with the table driven scheme adding new MSRs is very cheap
(just a table entry usually) so there is little reason for not adding any.

-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/