linux-kernel - Re: [PATCH] virtual sched

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Message-Id: <1184879223.5516.45.camel@localhost.localdomain>
Date:	Thu, 19 Jul 2007 21:07:03 +0000
From:	Jan Glauber <jang@...ux.vnet.ibm.com>
To:	Ingo Molnar <mingo@...e.hu>
Cc:	Jeremy Fitzhardinge <jeremy@...p.org>,
	LKML <linux-kernel@...r.kernel.org>, vatsa@...ux.vnet.ibm.com,
	mschwid2@...ux.vnet.ibm.com, efault@....de,
	dmitry.adamushko@...il.com, paulus@...ba.org, anton@...ba.org
Subject: Re: [PATCH] virtual sched_clock() for s390

On Thu, 2007-07-19 at 21:38 +0200, Ingo Molnar wrote: 
> * Jan Glauber <jang@...ux.vnet.ibm.com> wrote:
> 
> > > still, CFS needs time measurement across idle periods as well, for 
> > > another purpose: to be able to do precise task statistics for /proc. 
> > > (for top, ps, etc.) So it's still true that sched_clock() should 
> > > include idle periods too.
> > 
> > I'm not sure, s390 already has an implemetation for precise accounting 
> > in the architecture code, does CFS also improve accounting data?
> 
> what kind of precise accounting does s390 have in the architecture code? 
> CFS changes task (and load) accounting to be sched_clock() driven in 
> essence.

s390 has per-process accounting that is aware of virtual cpu time, implemented in
arch/s390/kernel/time.c: account_ticks() and arch/s390/kernel/vtime.c:
account_*_vtime(). Timestamps are taken in entry.S for system calls, interrupts
and other system entries and are accounted later, we don't call update_process_times().

Jan

> 	Ingo
> -
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