netdev - Re: rps perfomance WAS(Re: rps: question

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Date:	Tue, 20 Apr 2010 08:02:21 -0400
From:	jamal <hadi@...erus.ca>
To:	Eric Dumazet <eric.dumazet@...il.com>
Cc:	Changli Gao <xiaosuo@...il.com>, Rick Jones <rick.jones2@...com>,
	David Miller <davem@...emloft.net>, therbert@...gle.com,
	netdev@...r.kernel.org, robert@...julf.net, andi@...stfloor.org
Subject: Re: rps perfomance WAS(Re: rps: question

folks,

Thanks to everybody (Eric stands out) for your patience. 
I ended mostly validating whats already been said. I have a lot of data
and can describe in details how i tested etc but it would require
patience in reading, so i will spare you;-> If you are interested let me
know and i will be happy to share.

Summary is: 
-rps good, gives higher throughput for apps
-rps not so good, latency worse but gets better with higher input rate
or increasing number of flows (which translates to higher pps)
-rps works well with newer hardware that has better cache structures.
[Gives great results on my test machine a Nehalem single processor, 4
cores each with two SMT threads that has a shared L2 between threads and
a shared L3 between cores]. 
Your selection of what the demux cpu is and where the target cpus are is
an influencing factor in the latency results. If you have a system with
multiple sockets, you should get better numbers if you stay within the
same socket relative to going across sockets.
-rps does a better job at helping schedule apps on same cpu thus
localizing the app. The throughput results with rps are very consistent
and better whereas in non-rps case, variance is _high_.

My next step is to do some forwarding tests - probably next week. I am
concerned here because i expect the cache misses to be higher than the
app scenario (netdev structure and attributes could be touched by many
cpus)

cheers,
jamal

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