On Fri, 2012-06-01 at 00:42 +0200, Jan Kara wrote:
> On Fri 01-06-12 00:26:05, Peter Zijlstra wrote:
> > On Fri, 2012-06-01 at 00:11 +0200, Jan Kara wrote:
> > > bool fprop_new_period(struct fprop_global *p, int periods)
> > > {
> > > - u64 events = percpu_counter_sum(&p->events);
> > > + u64 events;
> > > + unsigned long flags;
> > >
> > > + local_irq_save(flags);
> > > + events = percpu_counter_sum(&p->events);
> > > + local_irq_restore(flags);
> > > /*
> > > * Don't do anything if there are no events.
> > > */
> > > @@ -73,7 +77,9 @@ bool fprop_new_period(struct fprop_global *p, int periods)
> > > if (periods < 64)
> > > events -= events >> periods;
> > > /* Use addition to avoid losing events happening between sum and set */
> > > + local_irq_save(flags);
> > > percpu_counter_add(&p->events, -events);
> > > + local_irq_restore(flags);
> > > p->period += periods;
> > > write_seqcount_end(&p->sequence);
> >
> > Uhm, why bother enabling it in between? Just wrap the whole function in
> > a single IRQ disable.
> I wanted to have interrupts disabled for as short as possible but if you
> think it doesn't matter, I'll take your advice. The result is attached.
Thing is, disabling interrupts is quite expensive and the extra few
instructions covered isn't much.
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