Re: Gigabit/SMP performance problem

Avery Fay
2003-01-06T21:25:46Z

Hmm. That paper is actually very interesting. I'm thinking maybe with the
P4 I'm better off with only 1 cpu. WRT hyperthreading, I actually disabled
it because it make performance worse (wasn't clear in the original email).

Avery Fay

Anton Blanchard <anton@samba.org>
01/03/2003 10:33 PM

To: Avery Fay <avery_fay@symantec.com>
cc: linux-kernel@vger.kernel.org
Subject: Re: Gigabit/SMP performance problem

> I'm working with a dual xeon platform with 4 dual e1000 cards on
different
> pci-x buses. I'm having trouble getting better performance with the
second
> cpu enabled (ht disabled). With a UP kernel (redhat's 2.4.18), I can
route
> about 2.9 gigabits/s at around 90% cpu utilization. With a SMP kernel
> (redhat's 2.4.18), I can route about 2.8 gigabits/s with both cpus at
> around 90% utilization. This suggests to me that the network code is
> serialized. I would expect one of two things from my understanding of
the
> 2.4.x networking improvements (softirqs allowing execution on more than
> one cpu):

The Fujitsu guys have a nice summary of this:

http://www.labs.fujitsu.com/en/techinfo/linux/lse-0211/index.html

Skip forward to page 8.

Dont blame the networking code just yet :) Notice how worse UP vs SMP
performance is on the P4 compared to the P3?

This brings up another point, is a single CPU with hyperthreading worth
it? As Rusty will tell you, you need to compare it with a UP kernel
since it avoids all the locking overhead. I suspect for a lot of cases
HT will be a loss (imagine your case, comparing UP and one CPU HT)

Anton