linux-kernel - Re: [PATCH v2 net-next] softirq: reduce latencies

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Message-Id: <20130104.134910.1157297903826332014.davem@davemloft.net>
Date:	Fri, 04 Jan 2013 13:49:10 -0800 (PST)
From:	David Miller <davem@...emloft.net>
To:	eric.dumazet@...il.com
Cc:	bhutchings@...arflare.com, akpm@...ux-foundation.org,
	netdev@...r.kernel.org, linux-kernel@...r.kernel.org,
	therbert@...gle.com
Subject: Re: [PATCH v2 net-next] softirq: reduce latencies

From: Eric Dumazet <eric.dumazet@...il.com>
Date: Thu, 03 Jan 2013 23:49:40 -0800

> From: Eric Dumazet <edumazet@...gle.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
> 
> When one of this condition is met, we wakeup ksoftirqd for further
> softirq processing if we still have pending softirqs.
 ...
> Signed-off-by: Eric Dumazet <edumazet@...gle.com>

Acked-by: David S. Miller <davem@...emloft.net>
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