netdev - Re: [PATCH v2] rfs: Receive Flow Steering

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Message-ID: <1270566652.2081.38.camel@edumazet-laptop>
Date:	Tue, 06 Apr 2010 17:10:52 +0200
From:	Eric Dumazet <eric.dumazet@...il.com>
To:	Tom Herbert <therbert@...gle.com>
Cc:	davem@...emloft.net, netdev@...r.kernel.org
Subject: Re: [PATCH v2] rfs: Receive Flow Steering

Le mardi 06 avril 2010 à 07:25 -0700, Tom Herbert a écrit :

> > 2) inet_rps_save_rxhash(sk, skb->rxhash);
> >
> >        It should have a check to make sure some part of the stack doesnt feed
> > many different rxhash for a given socket (Make sure we dont pollute flow
> > table with pseudo random values)
> >
> If packets for a connection are always received on the same device, is
> it reasonable to assume the rxhash is constant for that connection?
> 
> I suppose it's possible that packets for a same sockets are being
> constantly received on two different devices that are giving different
> rxhashes.  This would already be bad in that OOO is probably happening
> anyway.  I don't know if thrashing the sock_flow_table is going to
> aggravate this scenario much.
> 
> Are there any other degenerative cases you're worried about?

No, I was only considering this mostly as a debugging aid, before RPS is
stable, because mismatches could be unnoticed and performance not
optimal.
 


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