netdev - Re: small RPS cache for fragments?

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Date:	Mon, 06 Jun 2011 10:08:52 -0700
From:	Rick Jones <rick.jones2@...com>
To:	David Miller <davem@...emloft.net>
Cc:	netdev@...r.kernel.org
Subject: Re: small RPS cache for fragments?

On Sat, 2011-06-04 at 13:29 -0700, David Miller wrote:
> From: Rick Jones <rick.jones2@...com>
> Date: Tue, 24 May 2011 14:38:48 -0700
> 
> > Isn't there still an issue (perhaps small) of traffic being sent through
> > a mode-rr bond, either at the origin or somewhere along the way?  At the
> > origin point will depend on the presence of UFO and whether it is
> > propagated up through the bond interface, but as a quick test, I
> > disabled TSO, GSO and UFO on four e1000e driven interfaces, bonded them
> > mode-rr and ran a netperf UDP_RR test with a 1473 byte request size and
> > this is what they looked like at my un-bonded reciever at the other end:
> > 
> > 14:31:01.011370 IP (tos 0x0, ttl 64, id 24960, offset 1480, flags
> > [none], proto UDP (17), length 21)
> >     tardy.local > raj-8510w.local: udp
> > 14:31:01.011420 IP (tos 0x0, ttl 64, id 24960, offset 0, flags [+],
> > proto UDP (17), length 1500)
> >     tardy.local.36073 > raj-8510w.local.59951: UDP, length 1473
> > 14:31:01.011514 IP (tos 0x0, ttl 64, id 0, offset 0, flags [DF], proto
> > UDP (17), length 29)
> >     raj-8510w.local.59951 > tardy.local.36073: UDP, length 1
> 
> That's not good behavior, and it's of course going to cause sub-optimal
> performance if we do the RPS fragment cache.
> 
> RR bond mode could do something similar, to alleviate this.
> 
> I assume it doesn't do this kind of reordering for TCP.

Mode-rr bonding reorders TCP segments all the time. 

rick

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