netdev - RE: [ofa-general] Re: [PATCH 2/3][NET

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Date:	Wed, 10 Oct 2007 09:42:28 -0700
From:	"Waskiewicz Jr, Peter P" <peter.p.waskiewicz.jr@...el.com>
To:	"Andi Kleen" <andi@...stfloor.org>
Cc:	"David Miller" <davem@...emloft.net>, <hadi@...erus.ca>,
	<shemminger@...ux-foundation.org>, <jeff@...zik.org>,
	<johnpol@....mipt.ru>, <herbert@...dor.apana.org.au>,
	<gaagaan@...il.com>, <Robert.Olsson@...a.slu.se>,
	<netdev@...r.kernel.org>, <rdreier@...co.com>,
	<mcarlson@...adcom.com>, <jagana@...ibm.com>,
	<general@...ts.openfabrics.org>, <mchan@...adcom.com>,
	<tgraf@...g.ch>, <randy.dunlap@...cle.com>, <sri@...ibm.com>,
	<kaber@...sh.net>
Subject: RE: [ofa-general] Re: [PATCH 2/3][NET_BATCH] net core use batching

> -----Original Message-----
> From: Andi Kleen [mailto:andi@...stfloor.org] 
> Sent: Wednesday, October 10, 2007 9:02 AM
> To: Waskiewicz Jr, Peter P
> Cc: David Miller; andi@...stfloor.org; hadi@...erus.ca; 
> shemminger@...ux-foundation.org; jeff@...zik.org; 
> johnpol@....mipt.ru; herbert@...dor.apana.org.au; 
> gaagaan@...il.com; Robert.Olsson@...a.slu.se; 
> netdev@...r.kernel.org; rdreier@...co.com; 
> mcarlson@...adcom.com; jagana@...ibm.com; 
> general@...ts.openfabrics.org; mchan@...adcom.com; 
> tgraf@...g.ch; randy.dunlap@...cle.com; sri@...ibm.com; 
> kaber@...sh.net
> Subject: Re: [ofa-general] Re: [PATCH 2/3][NET_BATCH] net 
> core use batching
> 
> > We've done similar testing with ixgbe to push maximum descriptor 
> > counts, and we lost performance very quickly in the same 
> range you're 
> > quoting on NIU.
> 
> Did you try it with WC writes to the ring or CLFLUSH?
> 
> -Andi

Hmm, I think it might be slightly different, but it still shows queue
depth vs. performance.  I was actually referring to how many descriptors
we can represent a packet with before it becomes a problem wrt
performance.  This morning I tried to actually push my ixgbe NIC hard
enough to come close to filling the ring with packets (384-byte
packets), and even on my 8-core Xeon I can't do it.  My system can't
generate enough I/O to fill the hardware queues before CPUs max out.

-PJ Waskiewicz
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