Date: Fri, 13 Mar 2009 11:51:37 -0700 (PDT)
Message-Id: <20090313.115137.254924980.davem@davemloft.net>
To: therbert@google.com
Cc: yanmin_zhang@linux.intel.com, bhutchings@solarflare.com,
       andi@firstfloor.org, netdev@vger.kernel.org,
       linux-kernel@vger.kernel.org, herbert@gondor.apana.org.au,
       jesse.brandeburg@intel.com, shemminger@vyatta.com
Subject: Re: [RFC v2: Patch 1/3] net: hand off skb list to other cpu to
 submit to upper layer
From: David Miller <davem@davemloft.net>
In-Reply-To: <65634d660903131006n44f068dw18b2fe9dce25399e@mail.gmail.com>
References: <1236866906.3221.11.camel@achroite>
	<1236926602.2567.528.camel@ymzhang>
	<65634d660903131006n44f068dw18b2fe9dce25399e@mail.gmail.com>
Mime-Version: 1.0
Content-Type: Text/Plain; charset=us-ascii
Content-Transfer-Encoding: 7bit
Sender: linux-kernel-owner@vger.kernel.org
Content-Length: 1329
Lines: 26

From: Tom Herbert <therbert@google.com>
Date: Fri, 13 Mar 2009 10:06:56 -0700

> You'll definitely want to look at the hardware provided hash.  We've
> been using a 10G NIC which provides a Toeplitz hash (the one defined
> by Microsoft) and a software RSS-like capability to move packets from
> an interrupting CPU to another for processing.  The hash could be used
> to index to a set of CPUs, but we also use the hash as a connection
> identifier to key into a lookup table to steer packets to the CPU
> where the application is running based on the running CPU of the last
> recvmsg.  Using the device provided hash in this manner is a HUGE win,
> as opposed to taking cache misses to get 4-tuple from packet itself to
> compute a hash.  I posted some patches a while back on our work if
> you're interested.

I never understood this.

If you don't let the APIC move the interrupt around, the individual
MSI-X interrupts will steer packets to individual specific CPUS and as
a result the scheduler will migrate tasks over to those cpus since the
wakeup events keep occuring there.
--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@vger.kernel.org
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/