From: Arjan van de Ven <arjan@infradead.org>
To: Corrado Zoccolo <czoccolo@gmail.com>
Cc: linux-kernel@vger.kernel.org,
Andrew Morton <akpm@linux-foundation.org>,
lenb@kernel.org, mingo@elte.hu, yanmin_zhang@linux.intel.com,
jens.axboe@oracle.com, Ivan Kokshaysky <ink@jurassic.park.msu.ru>
Subject: Re: [PATCH v2] cpuidle: Fix the menu governor to boost IO performance
Date: Sun, 8 Nov 2009 14:30:59 -0800 [thread overview]
Message-ID: <20091108143059.029abf8b@infradead.org> (raw)
In-Reply-To: <4e5e476b0911081359x32d7a6c4x61ee3af92dc0c8a1@mail.gmail.com>
On Sun, 8 Nov 2009 22:59:43 +0100
Corrado Zoccolo <czoccolo@gmail.com> wrote:
> >
> > the exit latency is +/- 1 us, the entry latency is similar, and then
> > you're pretty close to 5 already (esp if you keep in mind that to
> > break even on energy you also need to be in the C state for a
> > little bit)...
>
> There are also performance considerations for using C1 (HLT).
> Quoting from http://www.intel.com/Assets/PDF/manual/248966.pdf (8-19):
> On processors supporting HT Technology, operating systems should use
> the HLT instruction if one logical processor is active and the other
> is not. HLT will allow an idle
> logical processor to transition to a halted state; this allows the
> active logical
> processor to use all the hardware resources in the physical package.
I think we all agree that long term polling is bad ;-)
(even though we use rep nop in the polling loop which is also a HT
yield).
There's just the very short sleeps (where short is "single digit usecs")
where the rules are slightly different.
> > this check is supposed to catch the known timer cases; those
> > are rather accurate in prediction
>
> Unfortunately, I have seen polling residency times > 1ms, so it must
> not be so accurate.
well the question is... is this a measurement error or an error in
when polling is chosen.
We obviously need to fix it whatever it is, but... first need to chase
down really which it is.
--
Arjan van de Ven Intel Open Source Technology Centre
For development, discussion and tips for power savings,
visit http://www.lesswatts.org
next prev parent reply other threads:[~2009-11-08 22:29 UTC|newest]
Thread overview: 14+ messages / expand[flat|nested] mbox.gz Atom feed top
2009-09-15 3:42 [PATCH v2] cpuidle: Fix the menu governor to boost IO performance Arjan van de Ven
2009-09-15 3:54 ` Andrew Morton
2009-09-15 4:15 ` Arjan van de Ven
2009-09-15 4:18 ` Arjan van de Ven
2009-09-15 5:03 ` Rik van Riel
2009-09-15 23:23 ` Andrew Morton
2009-09-16 4:35 ` Arjan van de Ven
2009-09-17 13:39 ` Arjan van de Ven
2009-11-04 9:39 ` Corrado Zoccolo
2009-11-08 20:40 ` Arjan van de Ven
2009-11-08 21:59 ` Corrado Zoccolo
2009-11-08 22:30 ` Arjan van de Ven [this message]
2009-11-09 13:29 ` Corrado Zoccolo
2009-11-08 22:39 ` Arjan van de Ven
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