netdev - Re: [PATCH] rfs: Receive Flow Steering

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Date:	Fri, 2 Apr 2010 21:45:12 +0800
From:	Changli Gao <xiaosuo@...il.com>
To:	Eric Dumazet <eric.dumazet@...il.com>
Cc:	Tom Herbert <therbert@...gle.com>, davem@...emloft.net,
	netdev@...r.kernel.org
Subject: Re: [PATCH] rfs: Receive Flow Steering

On Fri, Apr 2, 2010 at 8:01 PM, Eric Dumazet <eric.dumazet@...il.com> wrote:
> Le vendredi 02 avril 2010 à 18:58 +0800, Changli Gao a écrit :
>
> This dispatch things in UserLand is a poor workaround even if its
> popular (because people try to code portable applications), the hard
> work is already done, this increases latencies and bus traffic.
>
> For short works, that is too expensive.

I'll write a sample program to verify it. For TCP progam, I think it
won't be too expensive.

>
> If you really want to speedup memcached/DNS_server like apps, you might
> add a generic mechanism in kernel to split queues of _individual_
> socket.
>
> Aka multiqueue capabilities at socket level. Combined to multiqueue
> devices or RPS, this can be great.
>
>
> That is, an application tells kernel in how many queues incoming UDP
> frames for a given port can be dispatched (number of worker threads)
> No more contention, and this can be done regardless of RPS/RFS.
>
> UDP frame comes in, and is stored on the appropriate sub-queue (can be a
> mapping given by current cpu number). Wakeup the thread that is likely
> running on same cpu.
>
> Same for outgoing frames (answers). You might split the sk_wmemalloc
> thing to make sure several cpus can concurrently use same UDP socket to
> send their frames.
>

Yea. It much likes my another idea: selective wakeup. Always try to
wake up the sleeping process which is likely running on the same cpu.

-- 
Regards，
Changli Gao(xiaosuo@...il.com)
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