From: Sujit K M <sjt.kar@gmail.com>
To: Pradyumna Sampath <pradysam@gmail.com>
Cc: linux-rt-users@vger.kernel.org, rachana.rao@in.abb.com
Subject: Re: mq_timedrecieve timeout accuracy
Date: Wed, 24 Mar 2010 18:51:25 +0530 [thread overview]
Message-ID: <921ca19c1003240621k226df80ct62b3fb2e26269eca@mail.gmail.com> (raw)
In-Reply-To: <6d09081c1003240527r471ee34etbba11b4b7c7e92b3@mail.gmail.com>
> stumbled upon the fact that the timeout in the mq_timedrecieve is
> innaccurate to the tune of a more than 5-6 miliseconds and that it is
> fairly consistent even at its highest priority.
OK.
>
> Cyclictest on the same machine gives me a max deviation of about 7uS,
> so I guess my timers (hrt) are functioning alright.
Out of how much? What is the range of the timer.
> Here is a small program I hacked up from the LTP sources to
> demonstrate this behaviour (attached). I ran this on a dual core
> 2.5Ghz cpu and a uniprocessor 1.5Ghz cpu (cpuinfo below). On the
> dual-core I can see that its off by 1-2 miliseconds but on the 1.5 Ghz
> celeron its off by 6-8 miliseconds sometimes.
Yes, but the cyclic test doesnot match with this result. Both are in
the negative.
How have you tested the patch.
>
> kernel version: 2.6.33.1-rt10
>
> Usage: ./send_rev_2 <timeout_in_miliseconds>
>
> $ cat /proc/cpuinfo
> processor : 0
> vendor_id : GenuineIntel
> cpu family : 6
> model : 13
> model name : Intel(R) Celeron(R) M processor 1.50GHz
> stepping : 8
> cpu MHz : 1500.111
> cache size : 1024 KB
> fdiv_bug : no
> hlt_bug : no
> f00f_bug : no
> coma_bug : no
> fpu : yes
> fpu_exception : yes
> cpuid level : 2
> wp : yes
> flags : fpu vme de pse tsc msr pae mce cx8 apic sep mtrr pge mca cmov
> clflush dts acpi mmx fxsr sse sse2 ss tm pbe nx up bts
>
> Also attaached is my .config.
>
> thanks in advance
> regards
> /prady
>
>
> --
> http://www.prady.in
>
--
-- Sujit K M
blog(http://kmsujit.blogspot.com/)
--
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next prev parent reply other threads:[~2010-03-24 13:21 UTC|newest]
Thread overview: 11+ messages / expand[flat|nested] mbox.gz Atom feed top
2010-03-24 12:27 mq_timedrecieve timeout accuracy Pradyumna Sampath
2010-03-24 13:12 ` John Kacur
2010-03-24 13:21 ` Sujit K M [this message]
2010-03-24 13:22 ` M. Koehrer
2010-03-24 13:37 ` Pradyumna Sampath
2010-03-24 13:45 ` Sujit K M
2010-03-24 13:47 ` Pradyumna Sampath
2010-03-24 14:03 ` Pradyumna Sampath
2010-03-24 15:46 ` [PATCH] " Pradyumna Sampath
2010-03-29 15:08 ` [PATCH] " Carsten Emde
2010-03-30 7:41 ` Pradyumna Sampath
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