(fixed the subject to include the patch title. Patch quoted below.)
* Ingo Molnar <mi...@kernel.org> wrote:
>
> * Ingo Molnar <mi...@kernel.org> wrote:
>
> > This would speed up various hrtimer primitives like
> > hrtimer_remove()/add and simplify the code. It would be a net code
> > shrink as well.
> >
> > Totally untested patch below. It gives:
> >
> > text data bss dec hex filename
> > 7502 427 0 7929 1ef9 hrtimer.o.before
> > 7422 427 0 7849 1ea9 hrtimer.o.after
> >
> > and half of that code removal is from hot paths.
> >
> > This would simplify the followup step of skipping over inactive bases
> > as well.
>
> The followup step is attached below (untested as well).
>
> Note that all other iterations already had a check for active.next, so
> the patch doesn't even bloat anything:
>
> text data bss dec hex filename
> 7422 427 0 7849 1ea9 hrtimer.o.before
> 7422 427 0 7849 1ea9 hrtimer.o.after
>
> (I did a rename within migrate_hrtimers() because it used 'cpu_base'
> vs 'clock_base' inconsistently in a confusing (to me) manner.)
>
> I'd also suggest the removal of the timerqueue_getnext() obfuscation:
> it 'sounds' complex but in reality it's a simple dereference to
> active.next. I think this is what triggered this rather pointless
> maintenance of active_bases.
>
> Thanks,
>
> Ingo
>
> ---
> kernel/time/hrtimer.c | 24 +++++++++++++++---------
> 1 file changed, 15 insertions(+), 9 deletions(-)
>
> Index: tip/kernel/time/hrtimer.c
> ===================================================================
> --- tip.orig/kernel/time/hrtimer.c
> +++ tip/kernel/time/hrtimer.c
> @@ -1660,29 +1660,35 @@ static void migrate_hrtimer_list(struct
>
> static void migrate_hrtimers(int scpu)
> {
> - struct hrtimer_cpu_base *old_base, *new_base;
> + struct hrtimer_cpu_base *old_cpu_base, *new_cpu_base;
> int i;
>
> BUG_ON(cpu_online(scpu));
> tick_cancel_sched_timer(scpu);
>
> local_irq_disable();
> - old_base = &per_cpu(hrtimer_bases, scpu);
> - new_base = this_cpu_ptr(&hrtimer_bases);
> + old_cpu_base = &per_cpu(hrtimer_bases, scpu);
> + new_cpu_base = this_cpu_ptr(&hrtimer_bases);
> /*
> * The caller is globally serialized and nobody else
> * takes two locks at once, deadlock is not possible.
> */
> - raw_spin_lock(&new_base->lock);
> - raw_spin_lock_nested(&old_base->lock, SINGLE_DEPTH_NESTING);
> + raw_spin_lock(&new_cpu_base->lock);
> + raw_spin_lock_nested(&old_cpu_base->lock, SINGLE_DEPTH_NESTING);
>
> for (i = 0; i < HRTIMER_MAX_CLOCK_BASES; i++) {
> - migrate_hrtimer_list(&old_base->clock_base[i],
> - &new_base->clock_base[i]);
> + struct hrtimer_clock_base *old_base = old_cpu_base->clock_base
> + i;
> + struct hrtimer_clock_base *new_base;
> +
> + if (!old_base->active.next)
> + continue;
> +
> + new_base = new_cpu_base->clock_base + i;
> + migrate_hrtimer_list(old_base, new_base);
> }
>
> - raw_spin_unlock(&old_base->lock);
> - raw_spin_unlock(&new_base->lock);
> + raw_spin_unlock(&old_cpu_base->lock);
> + raw_spin_unlock(&new_cpu_base->lock);
>
> /* Check, if we got expired work to do */
> __hrtimer_peek_ahead_timers();
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