netdev - Re: [WIP][PATCHES] Network xmit batching

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Message-ID: <OFE747F0A6.D87A0584-ON652572F4.001AE91F-652572F4.001C1B29@in.ibm.com>
Date:	Fri, 8 Jun 2007 10:36:59 +0530
From:	Krishna Kumar2 <krkumar2@...ibm.com>
To:	hadi@...erus.ca
Cc:	David Miller <davem@...emloft.net>,
	Gagan Arneja <gaagaan@...il.com>,
	Evgeniy Polyakov <johnpol@....mipt.ru>, netdev@...r.kernel.org,
	Rick Jones <rick.jones2@...com>,
	Robert Olsson <Robert.Olsson@...a.slu.se>,
	Sridhar Samudrala <sri@...ibm.com>
Subject: Re: [WIP][PATCHES] Network xmit batching

Hi Jamal,

> Would be nice to run three sets - but i think even one would be
> sufficiently revealing.

I will try multiple runs over the weekend. During the week, the systems
are used for other purposes too.

> I expect UDP to overwhelm the receiver. So the receiver needs a lot more
> tuning (like increased rcv socket buffer sizes to keep up, IMO).

I will try that. Also on the receiver, I am using unmodified 2.6.21 bits.

> It seems to me any runs with buffer less than 512B are unable to fill
> the pipe - so will not really benefit (will probably do with nagling).
> However, the < 512 B should show equivalent results before and after the
> changes.

My earlier experiments showed that even small buffers were filling the
E1000
slots and resulting in stop queue very often. In any case, I will also
add 1 or 2 larger packet sizes (1K, 16K in addition to the 4K already
there).

> You can try to turn off _BTX feature in the driver and see if they are
> the same. If they are not, then the suspect change will be easy to find.

I was planning to submit my changes on top of this patch, and since it
includes
a configuration option per device, it will be easy to test with and without
this API. When I ran after setting this config option to 0, the results
were
almost identical to the original code. I will try to post that today for
your
review/comments.

> Sorry, been many moons since i last played with netperf; what does
"service
> demand" mean?

It gives an indication of the amount of CPU cycles to send out a particular
amount of data. Netperf provides it as us/KB. I don't know the internals of
netperf enough to say how this is calculated.

thanks,

- KK

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