Messages in this thread |  | | Date | Fri, 28 Sep 2001 19:46:43 +0200 (CEST) | From | Ingo Molnar <> | Subject | Re: [patch] softirq performance fixes, cleanups, 2.4.10. |
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On Fri, 28 Sep 2001 kuznet@ms2.inr.ac.ru wrote:
> More seriously, the question is not why these 10% appears, but rather > why they _disappeared_ in 2.4.7.
the effects i saw (Ben is not around unfortunately, so i cannot confirm neither deny whether there is any correlation between the effects Ben saw and the effects i saw) were due to ksoftirqd's generic tendency to increase the latency between the issuing of work and the completion of it. Increasing ksoftirqd's priority (in fact, setting current->counter = 2 everytime schedule() is called :-) does not fix this fundamental property => it still causes 'work generators' (processes) to use more CPU time than 'work completion' (irqs, softirqs). Furthermore, it also increases the latency between hardirqs and softirqs.
so my patch makes it sure that work is completed as soon as possible - but i've also kept an exit door open. [which you might find insufficient, but that i think is up to individual tuning anyway - i think i'm generally running faster machines than you, so our perspectives are slightly different.]
[processes are not always work generators, and irqs/softirqs not always do work completion, but i think generally they fit nicely into these two categories. Eg. the TCP stack often generates new work from softirqs, but IMO this does not change the fundamental equation.]
Ingo
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