netdev - Re: rps testing questions

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Date:	Mon, 17 Jan 2011 13:08:33 +0000
From:	Ben Hutchings <bhutchings@...arflare.com>
To:	mi wake <wakemi.wake@...il.com>
Cc:	netdev@...r.kernel.org
Subject: Re: rps testing questions

On Mon, 2011-01-17 at 17:43 +0800, mi wake wrote:
> I do a rps(Receive Packet Steering) testing on centos 5.5 with  kernel 2.6.37.
> cpu: 8 core Intel.
> ethernet adapter: bnx2x
> 
> Problem statement:
> enable rps with:
> echo "ff" > /sys/class/net/eth2/queues/rx-0/rps_cpus.
> 
> running 1 instances of netperf TCP_RR: netperf  -t TCP_RR -H 192.168.0.1 -c -C
> without rps: 9963.48(Trans Rate per sec)
> with rps:  9387.59(Trans Rate per sec)
> 
> I do ab and tbench testing also find there is less tps with enable
> rps.but,there is more cpu using when with enable rps.when with enable
> rps ，softirqs is blanced  on cpus.
> 
> is there something wrong with my test？

In addition to what Eric said, check the interrupt moderation settings
(ethtool -c/-C options).  One-way latency for a single request/response
test will be at least the interrupt moderation value.

I haven't tested RPS by itself (Solarflare NICs have plenty of hardware
queues) so I don't know whether it can improve latency.  However, RFS
certainly does when there are many flows.

Ben.

-- 
Ben Hutchings, Senior Software Engineer, Solarflare Communications
Not speaking for my employer; that's the marketing department's job.
They asked us to note that Solarflare product names are trademarked.

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