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Message-Id: <1271332528.4567.150.camel@bigi>
Date: Thu, 15 Apr 2010 07:55:28 -0400
From: jamal <hadi@...erus.ca>
To: David Miller <davem@...emloft.net>
Cc: eric.dumazet@...il.com, therbert@...gle.com,
netdev@...r.kernel.org, robert@...julf.net, xiaosuo@...il.com,
andi@...stfloor.org
Subject: Re: rps perfomance WAS(Re: rps: question
On Thu, 2010-04-15 at 01:48 -0700, David Miller wrote:
> A single-queue NIC is actually not a requirement,
> RPS helps also in cases where you have 'N' application threads
> and N is less than the number of CPUs your multi-queue NIC is
> distributing traffic to.
sure..
> Moving the bulk of the input packet processing to the cpus where
> the applications actually sit had a non-trivial benefit.
This is true regardless of rps though.
> RFS takes this aspect to yet another level.
rfs looks quiet interesting;-> I think with some twist it could be
used with multiqueue nics as well
> I think for the case where application locality is important,
> RPS/RFS can help regardless of cache details.
Generally true, as long as there's not much shared data across the cpus
or the cost of a cache miss is reasonably tolerable. The socket layer
just happens to be not sharing much with ingress packet path and
for a single processor Nehalem, the caching system works so well that
the cost of cache misses is not as an important a variable. Everything
is on the same die including the MM controller etc.
I am speculating (didnt get any answer to the question i asked) that
people running rps use such hardware;->
I speculate again that it may be too costly to run rps on something like
a tigerton or intel clovertown where you have cores sharing/contending
for an FSB. If I can get answers to the question: "What h/ware are
people running?" i could be proven wrong.
[Note: I am not against RPS - i think it has its place; so i hope my
desire to find out when to use rps doesnt show as hostility towards
rps.]
cheers,
jamal
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