From: Carsten Emde <C.Emde@osadl.org>
To: John Kacur <jkacur@redhat.com>
Cc: frank.rowand@am.sony.com, Simon Falsig <simon@newtec.dk>,
"linux-rt-users@vger.kernel.org" <linux-rt-users@vger.kernel.org>
Subject: Re: Real-time kernel thread performance and optimization
Date: Wed, 19 Dec 2012 16:20:58 +0100 [thread overview]
Message-ID: <50D1DB5A.7070708@osadl.org> (raw)
In-Reply-To: <alpine.LFD.2.02.1212191559180.4850@tycho>
Hi John,
>> [..]
>> If running a half-decent version of cyclictest, sleep states are generally
>> disabled while cyclictest is running. Please watch the line
>> # /dev/cpu_dma_latency set to 0us
>> which essentially documents this mechanism. Yes, the name of the variable
>> "cpu_dma_latency" is not obvious and cyclictest could do a better job by
>> writing
>> Wrote 0 to /dev/cpu_dma_latency and keeping the path open to prevent
>> all cores from entering any sleep state
>> but this is another story.
> Not sure what you mean here, doesn't it keep the path open?
No, no, cyclictest does the right thing and keeps the path open as
required. This is all good.
The message "/dev/cpu_dma_latency set to 0us" apparently is not clear
enough. It has nothing to do with DMA but the purpose of setting the
kernel variable cpu_dma_latency to 0 is to generally disable sleep
states. But I better should have submitted a patch.
-Carsten.
next prev parent reply other threads:[~2012-12-19 15:32 UTC|newest]
Thread overview: 16+ messages / expand[flat|nested] mbox.gz Atom feed top
2012-11-30 15:46 Real-time kernel thread performance and optimization Simon Falsig
2012-11-30 22:31 ` Frank Rowand
2012-12-03 12:39 ` Simon Falsig
2012-12-03 14:15 ` Carsten Emde
2012-12-11 14:43 ` Simon Falsig
2012-12-19 8:10 ` Carsten Emde
2012-12-20 8:09 ` Simon Falsig
2012-12-19 14:59 ` John Kacur
2012-12-19 15:20 ` Carsten Emde [this message]
2012-12-11 14:30 ` Simon Falsig
2012-12-17 22:18 ` Frank Rowand
2012-12-20 0:11 ` Darren Hart
2012-12-20 8:21 ` Simon Falsig
2013-01-02 17:21 ` Darren Hart
2012-12-12 15:39 ` Simon Falsig
-- strict thread matches above, loose matches on Subject: below --
2013-07-11 6:32 Simon Falsig
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