Messages in this thread |  | | Date | Mon, 26 May 2003 17:48:41 -0700 (PDT) | Subject | Re: userspace irq balancer | From | "David S. Miller" <> |
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From: Andrea Arcangeli <andrea@suse.de> Date: Tue, 27 May 2003 02:41:15 +0200
In 2.4 normally the softirq (of course w/o NAPI) are served in irq context so we didn't face this yet.
Andrea, whether ksoftirqd processes the softirq work or not has nothing to do with what I'm talking about.
It is all about what does a hardware IRQ mean in terms of work processed. And it can mean anything from 1 to 1000 packets worth of work.
Therefore, any usage of hardware IRQ activity to determine "load" in any sense is totally inaccurate.
So I'm asking you, again, how are you going to measure softirq load in making hardware IRQ load balancing decisions? Watching the scheduling and running of ksoftirqd is not an answer. Networking hardware interrupts, with a simplistic and mindless algorithm like the one we have currently in the 2.5.x IRQ balancing code, appear to be contributing very little to "load" and that is wrong.
But it doesn't change my basic argument about this topic, that there's no way in userspace to do anything remotely as accurate as that to boost system performance to the maximum, especially on big systems.
You show that the measurements and reactions belong there. This I totally understand. This is how cpufreq is implemented in 2.5.x currently. It is a very similar situation.
But deciding how to intepret these measurements and what to do in response is a userlevel policy decision. This also coincides with how cpufreq works. - To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
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