On Thu, Jan 23, 2014 at 05:55:39AM -0800, Kent Overstreet wrote:
> On Thu, Jan 23, 2014 at 02:50:03PM +0100, Peter Zijlstra wrote:
> > On Thu, Jan 23, 2014 at 05:28:29AM -0800, Kent Overstreet wrote:
> > > pool->lock is also going to be fairly badly contended in the worst case,
> > > and that can get real bad real fast... now that I think about it we
> > > probably want to avoid the __alloc_global_tag() double call just because
> > > of that, pool->lock is going to be quite a bit more contended than the
> > > waitlist lock just because fo the amount of work done under it.
> >
> > OK, how about this then.. Not quite at pretty though
>
> Heh, I suppose that is a solution. Let me screw around to see what I can
> come up with tomorrow, but if I can't come up with anything I like I'm
> not opposed to this.
Please also consider the below patch.
---
Subject: percpu-ida: Reduce IRQ held duration
Its bad manners to hold IRQs disabled over a full cpumask iteration.
Change it so that it disables the IRQs only where strictly required to
avoid lock inversion issues.
Signed-off-by: Peter Zijlstra <peterz@xxxxxxxxxxxxx>
---
--- a/lib/percpu_ida.c
+++ b/lib/percpu_ida.c
@@ -342,33 +342,31 @@ EXPORT_SYMBOL_GPL(__percpu_ida_init);
int percpu_ida_for_each_free(struct percpu_ida *pool, percpu_ida_cb fn,
void *data)
{
- unsigned long flags;
struct percpu_ida_cpu *remote;
- unsigned cpu, i, err = 0;
+ unsigned long flags;
+ int cpu, i, err = 0;
- local_irq_save(flags);
for_each_possible_cpu(cpu) {
remote = per_cpu_ptr(pool->tag_cpu, cpu);
- spin_lock(&remote->lock);
+ spin_lock_irqsave(&remote->lock, flags);
for (i = 0; i < remote->nr_free; i++) {
err = fn(remote->freelist[i], data);
if (err)
break;
}
- spin_unlock(&remote->lock);
+ spin_unlock_irqrestore(&remote->lock, flags);
if (err)
- goto out;
+ return err;
}
- spin_lock(&pool->lock);
+ spin_lock_irqsave(&pool->lock, flags);
for (i = 0; i < pool->nr_free; i++) {
err = fn(pool->freelist[i], data);
if (err)
break;
}
- spin_unlock(&pool->lock);
-out:
- local_irq_restore(flags);
+ spin_unlock_irqrestore(&pool->lock, flags);
+
return err;
}
EXPORT_SYMBOL_GPL(percpu_ida_for_each_free);
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