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    SubjectRE: [RFC] [PATCH] Performance of del_timer_sync
    Date
    >>>>> Andrew Morton wrote on Tuesday, May 11, 2004 1:12 PM
    > > > Ingo, why is this not sufficient?
    > >
    > > it's not sufficient because a timer might be running on another CPU even
    > > if it has not been deleted. We delete a timer prior running it (so that
    > > the timer fn can re-activate the timer). So del_timer_sync() has to
    > > synchronize independently of whether the timer was removed or not.
    > >
    >
    > Ah, OK, the timer handler may re-add itself. Really, that's a bug in the
    > caller: once they've decided to shoot down the timer the caller should have
    > made state changes which prevent the handler from re-adding the timer.
    >
    > Still, too late to change that.
    >
    > Neither AIO nor schedule_timeout() actually re-add the timer so they don't
    > need the full treatment, yes?
    >
    >
    > diff -puN kernel/timer.c~del-timer-speedup kernel/timer.c
    > --- 25/kernel/timer.c~del-timer-speedup 2004-05-11 13:05:41.997859088 -0700
    > +++ 25-akpm/kernel/timer.c 2004-05-11 13:07:32.493061264 -0700
    > @@ -348,8 +348,13 @@ del_again:
    >
    > return ret;
    > }
    > -
    > EXPORT_SYMBOL(del_timer_sync);
    > +
    > +int del_single_shot_timer(struct timer_struct *timer)
    > +{
    > + if (del_timer(timer))
    > + del_timer_sync(timer);
    > +}
    > #endif

    I'm confused, isn't the polarity of del_timer() need to be reversed?
    Also propagate the return value of del_timer_sync()?

    - Ken


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