Messages in this thread | | | Date | Fri, 16 Jan 2015 11:23:24 +0000 | From | Russell King - ARM Linux <> | Subject | Re: [RFC 2/2] clocksource: don't suspend/resume when unused |
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On Fri, Jan 16, 2015 at 11:35:30AM +0100, Alexandre Belloni wrote: > On 16/01/2015 at 11:23:32 +0100, Thomas Gleixner wrote : > > On Fri, 16 Jan 2015, Alexandre Belloni wrote: > > > > > There is no point in calling suspend/resume for unused > > > clocksources. > > > > > > Signed-off-by: Alexandre Belloni <alexandre.belloni@free-electrons.com> > > > --- > > > kernel/time/clocksource.c | 4 ++-- > > > 1 file changed, 2 insertions(+), 2 deletions(-) > > > > > > diff --git a/kernel/time/clocksource.c b/kernel/time/clocksource.c > > > index 920a4da58eb0..baea4e42ae90 100644 > > > --- a/kernel/time/clocksource.c > > > +++ b/kernel/time/clocksource.c > > > @@ -493,7 +493,7 @@ void clocksource_suspend(void) > > > struct clocksource *cs; > > > > > > list_for_each_entry_reverse(cs, &clocksource_list, list) > > > - if (cs->suspend) > > > + if (cs->suspend && (cs->flags & CLOCK_SOURCE_USED)) > > > cs->suspend(cs); > > > > This might be dangerous. If the clocksource has no enable/disable > > callbacks, but suspend/resume, then you might leave it enabled across > > suspend. > > > > Isn't that already the case? > Right now, if you call clocksource_suspend, it doesn't matter whether > the clocksource has an enable or not, it will be suspended. Maybe I'm > mistaken but my patch doesn't seem to change that behaviour.
You change an "always suspend" problem to a "never suspend" problem since those clocksources which are used, but do not have an ->enable callback will not be marked with CLOCK_SOURCE_USED.
Look at patch 1:
- if (!new->enable || new->enable(new) == 0) { + if (!new->enable || clocksource_enable(new) == 0) {
If new->enable is NULL, clocksource_enable() won't be called, which means there's nothing which sets CLOCK_SOURCE_USED, which in turn means that ->suspend() will never be called.
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