Re: Gigabit/SMP performance problem

Avery Fay
2003-01-06T21:17:53Z

Well, judging by the fact that a UP kernel can route more traffic (and
consequently more interrupts p/s) than an SMP kernel, I think that one cpu
can probably handle all of the interrupts. Really the issue I'm trying to
solve is not routing performance, but rather the fact that SMP routing
performance is worse while using twice the cpu time (2 cpu's at around 95%
vs. 1 at around 95%).

Avery Fay

"Martin J. Bligh" <mbligh@aracnet.com>
01/03/2003 04:36 PM

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

P3's distributed interrupts round-robin amongst cpus. P4's send
everything to CPU 0. If you put irq_balance on, it'll spread
them around, but any given interrupt is still only handled by
one CPU (as far as I understand the code). If you hammer one
adaptor, does that generate more interrupts than 1 cpu can handle?
(turn irq balance off by sticking a return at the top of balance_irq,
and hammer one link, see how much CPU power that burns).

M.