Re: [PATCH net-next] softirq: reduce latencies

Eric Dumazet
2013-01-03T22:40:19Z

On Thu, 2013-01-03 at 22:08 +0000, Ben Hutchings wrote:
> On Thu, 2013-01-03 at 04:28 -0800, Eric Dumazet wrote:
> > From: Eric Dumazet <edumazet@google.com>
> >
> > In various network workloads, __do_softirq() latencies can be up
> > to 20 ms if HZ=1000, and 200 ms if HZ=100.
> >
> > This is because we iterate 10 times in the softirq dispatcher,
> > and some actions can consume a lot of cycles.
> >
> > This patch changes the fallback to ksoftirqd condition to :
> >
> > - A time limit of 2 ms.
> > - need_resched() being set on current task
> [...]
> > --- a/kernel/softirq.c
> > +++ b/kernel/softirq.c
> [...]
> > -#define MAX_SOFTIRQ_RESTART 10
> > +#define MAX_SOFTIRQ_TIME min(1, (2*HZ/1000))
> [...]
>
> Really? Never iterate if HZ < 500?
>

good catch, it should be max()