From mboxrd@z Thu Jan  1 00:00:00 1970
From: Eric Dumazet <erdnetdev@gmail.com>
Subject: Re: [PATCH net-next] softirq: reduce latencies
Date: Thu, 03 Jan 2013 14:40:16 -0800
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Cc: David Miller <davem@davemloft.net>,
	Andrew Morton <akpm@linux-foundation.org>,
	netdev <netdev@vger.kernel.org>,
	"linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
	Tom Herbert <therbert@google.com>
To: Ben Hutchings <bhutchings@solarflare.com>
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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()