Messages in this thread | | | Date | Tue, 22 Apr 2003 17:54:33 -0400 (EDT) | From | Bill Davidsen <> | Subject | Re: irq balancing; kernel vs. userspace |
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---------- Forwarded message ---------- Subject: Re: irq balancing; kernel vs. userspace From: "Kevin P. Fleming" <kpfleming@cox.net> Date: Sun, 20 Apr 2003 11:37:00 -0700 To: linux-kernel@vger.kernel.org
Arjan van de Ven wrote:
> On Sun, 2003-04-20 at 15:23, Sean Neakums wrote: > >>I thought I'd play with the userspace IRQ-balancer, but booting with >>noirqbalance seems not to not balance. Possibly I misunderstand how >>this all fits together. > > > this looks like you haven't started the userspace daemon (yet)
I thought the same thing reading his original message, then I looked closer. He booted using "noirqbalance", did not start the userspace balancer, and yet his IRQs are still being balanced.
---------- Forwarded message ---------- Subject: Re: irq balancing; kernel vs. userspace From: Arjan van de Ven <arjanv@redhat.com> Date: 20 Apr 2003 21:10:18 +0200 To: "Kevin P. Fleming" <kpfleming@cox.net> Cc: linux-kernel@vger.kernel.org
On Sun, 2003-04-20 at 20:37, Kevin P. Fleming wrote:
> I thought the same thing reading his original message, then I looked > closer. He booted using "noirqbalance", did not start the userspace > balancer, and yet his IRQs are still being balanced.
if you don't do a thing, pIII cpu based machines will balance by themselves while pIV cpu based machines will redirect everything to CPU 0.
It would seem that there might be four commonly desirable modes of operation: 1 - All IRQ on CPU0 2 - Spread IRQ between all processors evenly 3 - Bind ints to CPUs to get about the same int count per CPU 4 - Fancy other stuff controlled by user app
Now (1) is what you get if you disable apic, Alan Cox recommends this on the smp list from time to time, and in most cases it works fine. Mode (2) is what happens on Pentium-III unless you prevent it. It has more cache overhead for some loads, but it's preferabe to trying to explain anything else to certain managers. Note the total lack of a smiley on that statement.
Now if that user program (4) could give me (2), and maybe even (1) with apic enabled for the really odd load and testing, I suspect that (3) is pretty much going to be included.
Think we could support a few other modes in the user tool and have the kernel default to either (1) or whatever the apic wants to do? And how does this map on non-Intel hardware?
-- bill davidsen <davidsen@tmr.com> CTO, TMR Associates, Inc Doing interesting things with little computers since 1979.
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