Subject: Re: [PATCH] ifb: add multi-queue support

From: Jarek Poplawski <[email-masked]>
Date: Fri, 13 Nov 2009 07:45:08 +0000

On 13-11-2009 07:16, Changli Gao wrote:
> 2009/11/13 Eric Dumazet <[email-masked]>:
>> Messy ? Because of few tests added in code, and branches always
>> correctly predicted ?
>>
>> Still some people might rely on tasklet instead of workqueues
>> and added scheduler stress and latency penalty. Tasklet are softirq
>> and normally are processed a few nanosecs later than RX softirq,
>> on the same CPU, while with your workqueue, I guess the scheduler will
>> try to not migrate it, so we add a penalty for light to moderate load.
>>
>> I guess this new ifb mode would be a regression for them ?
>>
>> If you dont want to maintain a compatibility mode, maybe you
>> should introduce a complete new driver, drivers/net/ifbmq.c or ifbwq.c
>>
>> (multiqueue or workqueue references)
>>
> 
> It sounds a good idea.

I don't think so. There would be a lot of code duplication and later
maintenance problems only because of the scheduling method. The main
question is to establish if there is really no performance difference
(which I doubt) - unless Changli can show some tests for various
setups now. On the other hand, if there is a difference, why keep
ineffective solution - similar thing should be possible to do in the
softirq context as well.

So it should not be a big problem to do it a bit messy for some
testing time. Since we can use separate ->ndo_start_xmit() etc. it
shouldn't be too messy, I guess.

Jarek P.