Re: [PATCH 01/19] freezer: don't get over-anxious while waiting

Rafael J. Wysocki
2009-10-01T21:02:39Z

On Thursday 01 October 2009, Pavel Machek wrote:
>
> > Freezing isn't exactly the most latency sensitive operation and
> > there's no reason to burn cpu cycles and power waiting for it to
> > complete. msleep(10) instead of yield(). This should improve
> > reliability of emergency hibernation.
>
> i don't see how it improves reliability, but its probably ok.
>
> Well... for hibernation anyway. I can imagine cgroup users where
> freeze is so fast that this matters. rjw cc-ed. pavel

Thanks. I'd like to hear from the cgroup freezer people about that.

> > Signed-off-by: Tejun Heo <tj@kernel.org>
> > ---
> > kernel/power/process.c | 13 +++++++++----
> > 1 files changed, 9 insertions(+), 4 deletions(-)
> >
> > diff --git a/kernel/power/process.c b/kernel/power/process.c
> > index cc2e553..9d26a0a 100644
> > --- a/kernel/power/process.c
> > +++ b/kernel/power/process.c
> > @@ -41,7 +41,7 @@ static int try_to_freeze_tasks(bool sig_only)
> > do_gettimeofday(&start);
> >
> > end_time = jiffies + TIMEOUT;
> > - do {
> > + while (true) {
> > todo = 0;
> > read_lock(&tasklist_lock);
> > do_each_thread(g, p) {
> > @@ -62,10 +62,15 @@ static int try_to_freeze_tasks(bool sig_only)
> > todo++;
> > } while_each_thread(g, p);
> > read_unlock(&tasklist_lock);
> > - yield(); /* Yield is okay here */
> > - if (time_after(jiffies, end_time))
> > + if (!todo || time_after(jiffies, end_time))
> > break;
> > - } while (todo);
> > +
> > + /*
> > + * We need to retry. There's no reason to be
> > + * over-anxious about it and waste power.
> > + */

The comment above looks like it's only meaningful in the context of the patch.
After it's been applied the meaning of the comment won't be so obvious, I'm
afraid.

> > + msleep(10);
> > + }
> >
> > do_gettimeofday(&end);
> > elapsed_csecs64 = timeval_to_ns(&end) - timeval_to_ns(&start);

Thanks,
Rafael