netdev - RE: >10% performance degradation since 2.6.18

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Date:	Mon, 6 Jul 2009 11:48:47 -0700
From:	"Ma, Chinang" <chinang.ma@...el.com>
To:	Matthew Wilcox <matthew@....cx>
CC:	Rick Jones <rick.jones2@...com>,
	Herbert Xu <herbert@...dor.apana.org.au>,
	Jeff Garzik <jeff@...zik.org>,
	"andi@...stfloor.org" <andi@...stfloor.org>,
	"arjan@...radead.org" <arjan@...radead.org>,
	"jens.axboe@...cle.com" <jens.axboe@...cle.com>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"Styner, Douglas W" <douglas.w.styner@...el.com>,
	"Prickett, Terry O" <terry.o.prickett@...el.com>,
	"Wilcox, Matthew R" <matthew.r.wilcox@...el.com>,
	"netdev@...r.kernel.org" <netdev@...r.kernel.org>,
	"Brandeburg, Jesse" <jesse.brandeburg@...el.com>
Subject: RE: >10% performance degradation since 2.6.18



>-----Original Message-----
>From: Matthew Wilcox [mailto:matthew@....cx]
>Sent: Monday, July 06, 2009 11:06 AM
>To: Ma, Chinang
>Cc: Rick Jones; Herbert Xu; Jeff Garzik; andi@...stfloor.org;
>arjan@...radead.org; jens.axboe@...cle.com; linux-kernel@...r.kernel.org;
>Styner, Douglas W; Prickett, Terry O; Wilcox, Matthew R;
>netdev@...r.kernel.org; Brandeburg, Jesse
>Subject: Re: >10% performance degradation since 2.6.18
>
>On Mon, Jul 06, 2009 at 10:57:09AM -0700, Ma, Chinang wrote:
>> >-----Original Message-----
>> >From: Matthew Wilcox [mailto:matthew@....cx]
>> >Sent: Monday, July 06, 2009 10:42 AM
>> >To: Ma, Chinang
>> >Cc: Rick Jones; Herbert Xu; Jeff Garzik; andi@...stfloor.org;
>> >arjan@...radead.org; jens.axboe@...cle.com; linux-kernel@...r.kernel.org;
>> >Styner, Douglas W; Prickett, Terry O; Wilcox, Matthew R;
>> >netdev@...r.kernel.org; Brandeburg, Jesse
>> >Subject: Re: >10% performance degradation since 2.6.18
>> >
>> >On Mon, Jul 06, 2009 at 10:36:11AM -0700, Ma, Chinang wrote:
>> >> For OLTP workload we are not pushing much network throughput. Lower
>> >network latency is more important for OLTP performance. For the original
>> >Nehalem 2 sockets OLTP result in this mail thread, we bound the two NIC
>> >interrupts to cpu1 and cpu9 (one NIC per sockets). Database processes
>are
>> >divided into two groups and pinned to socket and each processe only
>> >received request from the NIC it bound to. This binding scheme gave us
>>1%
>> >performance boost pre-Nehalem date. We also see positive impact on this
>NHM
>> >system.
>> >
>> >So you've tried spreading the four RX and TX interrupts for each card
>> >out over, say, CPUs 1, 3, 5, 7 for eth1 and then 9, 11, 13, 15 for eth0,
>> >and it produces worse performance than having all four tied to CPUs 1
>> >and 9?  Interesting.
>>
>> I was comparing 2 NIC on 2 sockets to 2 NIC on the same socket. I have
>not tried spreading out the interrupt for a NIC to cpus in the same sockets.
>Is there good reason for trying this?
>
>If spreading the network load from one CPU to two CPUs increases the
>performance, spreading the network load from two to eight might get even
>better performance.
>

On the distributing interrupt load subject.  Can we do the same thing with the IOC interrupts. We have 4 LSI 3801, The number of i/o interrupt is huge on 4 of the cpus. Is there a way to divide the IOC irq number so we can spread out the i/o interrupt to more cpu?


>Are the clients now pinned to the CPU package on which they receive their
>network interrupts?

Yes. The database processes in server are pinning to the socket on which they received network interrupts.

>
>> >Can you try changing IGB_MAX_RX_QUEUES (in drivers/net/igb/igb.h, about
>> >line 60) to 1, and seeing if performance improves that way?
>>
>> I suppose this should wait until we find out whether spread out NIC
>interrupt in socket helps or not.
>
>Yes, let's try having the driver work the way that LAD designed it
>first ;-)
>
>They may not have been optimising for the database client workload,
>of course.
>
>--
>Matthew Wilcox				Intel Open Source Technology Centre
>"Bill, look, we understand that you're interested in selling us this
>operating system, but compare it to ours.  We can't possibly take such
>a retrograde step."
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