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

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Message-ID: <87r4m1r0hm.fsf@sejong.aot.lge.com>
Date:	Fri, 04 Jan 2013 14:16:53 +0900
From:	Namhyung Kim <namhyung@...nel.org>
To:	Eric Dumazet <erdnetdev@...il.com>
Cc:	Andrew Morton <akpm@...ux-foundation.org>,
	David Miller <davem@...emloft.net>,
	netdev <netdev@...r.kernel.org>,
	"linux-kernel\@vger.kernel.org" <linux-kernel@...r.kernel.org>,
	Tom Herbert <therbert@...gle.com>
Subject: Re: [PATCH net-next] softirq: reduce latencies

Hi,

On Thu, 03 Jan 2013 14:41:15 -0800, Eric Dumazet wrote:
> On Thu, 2013-01-03 at 12:46 -0800, Andrew Morton wrote:
>> Can this change cause worsened latencies in some situations?  Say there
>> are a large number of short-running actions queued.  Presently we'll
>> dispatch ten of them and return.  With this change we'll dispatch many
>> more of them - however many consume 2ms.  So worst-case latency
>> increases from "10 * not-much" to "2 ms".
>
> I tried to reproduce such workload but couldnt. 2 ms (or more exactly 1
> to 2 ms given the jiffies/HZ granularity) is about the time needed to
> process 1000 frames on current hardware.

Probably a silly question:

Why not using ktime rather than jiffies for this?

Thanks,
Namhyung
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