linux-kernel - Re: [PATCH 2/2] CFS CGroup: Report usage

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Message-ID: <20071023164124.GA4666@linux.vnet.ibm.com>
Date:	Tue, 23 Oct 2007 22:11:24 +0530
From:	Srivatsa Vaddagiri <vatsa@...ux.vnet.ibm.com>
To:	"Paul Menage" <menage@...gle.com>
Cc:	"Andrew Morton" <akpm@...ux-foundation.org>,
	"Ingo Molnar" <mingo@...e.hu>,
	containers@...ts.linux-foundation.org,
	linux-kernel@...r.kernel.org, dmitry.adamushko@...il.com
Subject: Re: [PATCH 2/2] CFS CGroup: Report usage

On Mon, Oct 22, 2007 at 11:06:54PM -0700, Paul Menage wrote:
> > > +     for_each_possible_cpu(i) {
> > > +             unsigned long flags;
> > > +             spin_lock_irqsave(&tg->cfs_rq[i]->rq->lock, flags);
> >
> > Is the lock absolutely required here?
> 
> I'm not sure, I was hoping you or Ingo could comment on this. But some
> kind of locking seems to required at least on 32-bit platforms, since
> sum_exec_runtime is a 64-bit number.

I tend to agree abt 32-bit platforms requiring a lock to read the 64-bit
sum_exec_runtime field.

Ingo/Dmitry, what do you think? fs/proc/array.c:task_utime() is also
buggy in that case.

-- 
Regards,
vatsa
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