netdev - Re: Receive steering and hash and cache misses

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Date:	Fri, 02 Apr 2010 21:36:31 +0200
From:	Eric Dumazet <eric.dumazet@...il.com>
To:	Stephen Hemminger <shemminger@...tta.com>
Cc:	Tom Herbert <therbert@...gle.com>, netdev@...r.kernel.org
Subject: Re: Receive steering and hash and cache misses

Le vendredi 02 avril 2010 à 11:54 -0700, Stephen Hemminger a écrit :
> On Fri, 2 Apr 2010 10:59:43 -0700
> Tom Herbert <therbert@...gle.com> wrote:
> 
> > On Fri, Apr 2, 2010 at 10:26 AM, Stephen Hemminger
> > <shemminger@...tta.com> wrote:
> > >
> > > Although Receive Packet Steering can use a hardware generated receive hash
> > > the device driver still causes an unnecessary cache miss on the interrupt
> > > processing CPU.  The current Ethernet network device driver receive processing
> > > has the device driver calling eth_type_trans() which causes a the
> > > interrupt CPU to read the received frame header.
> > >
> > 
> > It should be possible to deduce the values set by eth_type_trans from
> > the RX descriptor along with the RX hash.  I'll post the patch getting
> > rxhash from bnx2x which does this.
> > 
> 
> On sky2, I get only RSS, Checksum, and length from descriptor info.

Doesnt sky2 also provide vlan id (OP_RXVLAN/OP_RXCHKSVLAN) ?

A future version of hardware could provide more info perhaps...

Must eth_type_trans() be done *before* netif_receive_skb() ?

If a device provides a rxhash, maybe we can delay eth_type_trans() too.
If not, we need to access IP header anyway in the first cpu.


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