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SubjectRe: [PATCH v2] proc: speedup /proc/stat handling
On Thu, 26 Jan 2012 16:43:42 -0800
Andrew Morton <akpm@linux-foundation.org> wrote:

> On Thu, 26 Jan 2012 18:55:20 +0900
> KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com> wrote:
>
> > On Wed, 25 Jan 2012 17:04:16 -0800
> > Andrew Morton <akpm@linux-foundation.org> wrote:
> >
> > > On Wed, 25 Jan 2012 06:29:32 +0100
> > > Eric Dumazet <eric.dumazet@gmail.com> wrote:
> > >
> > > > Le mardi 24 janvier 2012 __ 17:27 -0800, Andrew Morton a __crit :
> > > >
> > > > > I had a fiddle on an 8-way x86_64 machine. I'm unable to demonstrate
> > > > > any improvement for either of
> > > > >
> > > > > time (for i in $(seq 1000); do; cat /proc/self/stat > /dev/null; done)
> > > > > time (for i in $(seq 1000); do; cat /proc/1/stat > /dev/null; done)
> > > > >
> > > > > oh well.
> > > >
> > > > What size is /proc/stat ?
> > >
> > > About 40mm, but it depends on the font size.
> > >
> > > > wc -c /proc/stat
> > > >
> > > > If under 4096, there is no problem with existing code.
> > >
> > > akpm2:/home/akpm> wc -c /proc/stat
> > > 2800 /proc/stat
> > >
> > > > I had the problem on a 16-way machine.
> > >
> > > OK..
> >
> >
> > I wrote following patch just for my fun, which makes /proc/stat twice fast.
> > But I'm not sure whether this kind of dirty && special printk is worth to do or not..
> > because I can't see /proc/stat cost at shell-scripting.
>
> It is rather a lot of not-very-general infrastructure.
>
> >
> > ...
> >
> > @@ -131,8 +143,8 @@ static int show_stat(struct seq_file *p, void *v)
> > seq_printf(p, "intr %llu", (unsigned long long)sum);
> >
> > /* sum again ? it could be updated? */
> > - for_each_irq_nr(j)
> > - seq_printf(p, " %u", kstat_irqs(j));
> > + j = 0;
> > + seq_printnum_batch(p, " %u", &j, get_next_kstat_irq);
>
> I expect most of these numbers are zero. I wonder if we would get
> useful speedups from
>
> for_each_irq_nr(j) {
> /* Apologetic comment goes here */
> if (kstat_irqs(j))
> seq_printf(p, " %u", kstat_irqs(j));
> else
> seq_puts(p, " 0");
> }

Yes. This is very good optimization and shows much optimization.
I did this at first try but did complicated ones because it seems
not interesting. (This is my bad habit...)

I'll try again and measure time.

Thanks,
-Kame






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