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

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Message-ID: <1357250880.2685.29.camel@bwh-desktop.uk.solarflarecom.com>
Date:	Thu, 3 Jan 2013 22:08:00 +0000
From:	Ben Hutchings <bhutchings@...arflare.com>
To:	Eric Dumazet <eric.dumazet@...il.com>
CC:	David Miller <davem@...emloft.net>,
	Andrew Morton <akpm@...ux-foundation.org>,
	netdev <netdev@...r.kernel.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	Tom Herbert <therbert@...gle.com>
Subject: Re: [PATCH net-next] softirq: reduce latencies

On Thu, 2013-01-03 at 04:28 -0800, Eric Dumazet wrote:
> 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
[...]
> --- 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?

Ben.

-- 
Ben Hutchings, Staff Engineer, Solarflare
Not speaking for my employer; that's the marketing department's job.
They asked us to note that Solarflare product names are trademarked.

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