netdev - RE: [PATCH] mlx4_en: Setting RSS hash result to skb->rxhash field

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Date:	Thu, 5 May 2011 07:08:06 +0000
From:	Yevgeny Petrilin <yevgenyp@...lanox.co.il>
To:	Eric Dumazet <eric.dumazet@...il.com>
CC:	Ben Hutchings <bhutchings@...arflare.com>,
	"davem@...emloft.net" <davem@...emloft.net>,
	"netdev@...r.kernel.org" <netdev@...r.kernel.org>
Subject: RE: [PATCH] mlx4_en: Setting RSS hash result to skb->rxhash field

> > > >
> > > Eric, you are correct.
> > > We do plan to enable full 32 bit hash for our devices.
> > > Once it is done, we will naturally use the whole 32 bits.
> > > In the meanwhile, even with this change we see improved performance when enabling RPS.
> >
> > Hmm, thats strange because you have only 256 possible values for rxhash,
> > and it's OK for maybe one hundred flows. (I am talking not of RPS but
> > RFS here)
> >
> > So your patch is a win only for small hosts, or particular workloads
> > (did I say biased benchmarks ? ;) )
> >
> > Really, we better use the linux/software full 32bit rxhash in this case,
> > and wait for your 32bit full support.
> >
> >
> 
> BTW, before you submit another rxhash patch, please make sure ethtool
> support is included. An admin must be able to switch off hardware
> support :
> 
> ethtool -K eth0 rxhash off
> 
> 
Thanks for this input