linux-kernel - Re: [PATCH -tip] cpuacct: per-cgroup utime/stime statistics

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Date:	Mon, 23 Mar 2009 21:51:23 +0530
From:	Bharata B Rao <bharata@...ux.vnet.ibm.com>
To:	Andrew Morton <akpm@...ux-foundation.org>
Cc:	linux-kernel@...r.kernel.org, Balaji Rao <balajirrao@...il.com>,
	Dhaval Giani <dhaval@...ux.vnet.ibm.com>,
	Balbir Singh <balbir@...ux.vnet.ibm.com>,
	Li Zefan <lizf@...fujitsu.com>,
	Paul Menage <menage@...gle.com>, Ingo Molnar <mingo@...e.hu>,
	Peter Zijlstra <a.p.zijlstra@...llo.nl>,
	KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com>
Subject: Re: [PATCH -tip] cpuacct: per-cgroup utime/stime statistics - v4

On Mon, Mar 23, 2009 at 04:21:23AM -0700, Andrew Morton wrote:
> On Mon, 23 Mar 2009 10:05:38 +0530 Bharata B Rao <bharata@...ux.vnet.ibm.com> wrote:
> 
> > +static int cpuacct_stats_show(struct cgroup *cgrp, struct cftype *cft,
> > +		struct cgroup_map_cb *cb)
> > +{
> > +	struct cpuacct *ca = cgroup_ca(cgrp);
> > +	int i;
> > +
> > +	for (i = 0; i < CPUACCT_STAT_NSTATS; i++) {
> > +		s64 val = percpu_counter_read(&ca->cpustat[i]);
> > +		val = cputime_to_clock_t(val);
> > +		cb->fill(cb, cpuacct_stat_desc[i], val);
> > +	}
> > +	return 0;
> > +}
> 
> I'd have expected `val' to have type clock_t.  But clock_t is 32-bit on
> 32-bit x86.
> 
> Is it correct to pass a 64-bit value to a function which takes a 32-bit
> value and to then copy the 32-bit return value into a 64-bit variable?

Yes, doesn't look neat. Since the accumulated stat(val here) is of 64bit type,
I could use cputime64_to_clock_t(val) in the above code. Storing the resulting
32bit clock_t in a 64 bit variable(which will be used by cb->fill) should be
fine I believe. Let me know if I got this right.

Regards,
Bharata.
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