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Message-ID: <3f250c710603150640y95617e3sfa7c8f8db005290b@mail.gmail.com>
Date: Wed, 15 Mar 2006 10:40:34 -0400
From: "Mauricio Lin" <mauriciolin@gmail.com>
To: "Frank Ch. Eigler" <fche@redhat.com>
Subject: Re: Jiffy is not able to measure the fraction of time a process runs a processor
Cc: linux-kernel <linux-kernel@vger.kernel.org>, craig.lkml@gmail.com
In-Reply-To: <y0mveugagsm.fsf@ton.toronto.redhat.com>
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	 <y0mveugagsm.fsf@ton.toronto.redhat.com>
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Hi all,

I have managed to measure the cpu time in nanoseconds. On i386 I have used
the monotonic_clock() to measure the cpu time accurately.

The cpu time measurements were based on t->sched_info.cpu_time, but
instead of accumulate
the all cpu time, I needed just the diff=jiffies
-t->sched_info.last_arrival in the sched_info_depart().

The problem was most of time the diff was zero. So to solve this
problem I used the monotonic_clock() function that provides more accurate
way to measure cpu time.

Any comments?

On 14 Mar 2006 15:54:17 -0500, Frank Ch. Eigler <fche@redhat.com> wrote:
> "Mauricio Lin" <mauriciolin@gmail.com> writes:
>
> >  I am trying to measure the fraction of time a process runs on a
> > processor, but the jiffies is not able to provide an accurate value.
>
> See sched_clock().

I have checked it. It helped me to reach the monotonic_clock()
function after hacking the code.

>
> >  The example below [...]
> > PID  : NAME : LAST ARRIVAL : CPU TIME : CALLER
> > 4544 : kmix : 6170433 : 0 : work_resched+0x6c
> > 4078 : lpd : 6170433 : 0 : __down_interruptible+0x5
> > 4544 : kmix : 6170433 : 0 : schedule_timeout+0xb8
>
> What tool/patchset are you using to generate this trace?

I am using the relayfs to report the information I need among the
processors. I just put some klog in some key points in the code.

BR,

Mauricio Lin.
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