Re: Jiffy is not able to measure the fraction of time a process runs a processor

["Mauricio Lin" <mauriciolin@gmail.com>]

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.