Re: [PATCH -tip] cpuacct: per-cgroup utime/stime statistics - v4

[Bharata B Rao <bharata@linux.vnet.ibm.com>]

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@linux.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.