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

Ben Hutchings
2013-01-03T22:08:00Z

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?

Ben.

--
Ben Hutchings, Staff Engineer, Solarflare
Not speaking for my employer; that's the marketing department's job.
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