netdev - Re: [PATCH v5] rfs: Receive Flow Steering

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Message-ID: <t2y65634d661004200804r15427f19k9d58862f05df94aa@mail.gmail.com>
Date:	Tue, 20 Apr 2010 08:04:34 -0700
From:	Tom Herbert <therbert@...gle.com>
To:	Eric Dumazet <eric.dumazet@...il.com>
Cc:	Changli Gao <xiaosuo@...il.com>,
	David Miller <davem@...emloft.net>, netdev@...r.kernel.org
Subject: Re: [PATCH v5] rfs: Receive Flow Steering

On Mon, Apr 19, 2010 at 10:59 PM, Eric Dumazet <eric.dumazet@...il.com> wrote:
> Le mardi 20 avril 2010 à 07:38 +0800, Changli Gao a écrit :
>
>> Does this problem has relationship with your patch? No. If the rxhash
>> isn't provided by hardware, we can get more throughput from you patch,
>> and on the other side, we don't lose anything but potential more hash
>> collision.
>>
>
> I am not sure what you call hash collision. There is no hash chain here.
>
> This 32bit hash is a jhash one, and we only need 1 to 12 bits in it, I
> am pretty sure its OK.
>
Maybe for the purposes of RPS, but hash collisions could definitely be
an issue in RFS.  If two active connections hit the same rps_flow
entry this may cause thrashing of those connections between CPUs.  I
think your patch may increase the probability of this happening.

>
>
>
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