Messages in this thread | | | Date | Tue, 22 May 2007 09:51:29 +1000 | From | Peter Williams <> | Subject | Re: [patch] CFS scheduler, -v12 |
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Dmitry Adamushko wrote: > On 18/05/07, Peter Williams <pwil3058@bigpond.net.au> wrote: > [...] >> One thing that might work is to jitter the load balancing interval a >> bit. The reason I say this is that one of the characteristics of top >> and gkrellm is that they run at a more or less constant interval (and, >> in this case, X would also be following this pattern as it's doing >> screen updates for top and gkrellm) and this means that it's possible >> for the load balancing interval to synchronize with their intervals >> which in turn causes the observed problem. > > Hum.. I guess, a 0/4 scenario wouldn't fit well in this explanation..
No, and I haven't seen one.
> all 4 spinners "tend" to be on CPU0 (and as I understand each gets > ~25% approx.?), so there must be plenty of moments for > *idle_balance()* to be called on CPU1 - as gkrellm, top and X consume > together just a few % of CPU. Hence, we should not be that dependent > on the load balancing interval here..
The split that I see is 3/1 and neither CPU seems to be favoured with respect to getting the majority. However, top, gkrellm and X seem to be always on the CPU with the single spinner. The CPU% reported by top is approx. 33%, 33%, 33% and 100% for the spinners.
If I renice the spinners to -10 (so that there load weights dominate the run queue load calculations) the problem goes away and the spinner to CPU allocation is 2/2 and top reports them all getting approx. 50% each.
It's also worth noting that I've had tests where the allocation started out 2/2 and the system changed it to 3/1 where it stabilized. So it's not just a case of bad luck with the initial CPU allocation when the tasks start and the load balancing failing to fix it (which was one of my earlier theories).
> > (unlikely consiparacy theory)
It's not a conspiracy. It's just dumb luck. :-)
> - idle_balance() and load_balance() (the > later is dependent on the load balancing interval which can be in > sync. with top/gkerllm activities as you suggest) move always either > top or gkerllm between themselves.. esp. if X is reniced (so it gets > additional "weight") and happens to be active (on CPU1) when > load_balance() (kicked from scheduler_tick()) runs.. > > p.s. it's mainly theoretical specualtions.. I recently started looking > at the load-balancing code (unfortunatelly, don't have an SMP machine > which I can upgrade to the recent kernel) and so far for me it's > mainly about getting sure I see things sanely.
I'm playing with some jitter experiments at the moment. The amount of jitter needs to be small (a few tenths of a second) as the synchronization (if it's happening) is happening at the seconds level as the intervals for top and gkrellm will be in the 1 to 5 second range (I guess -- I haven't checked) and the load balancing is every 60 seconds.
Peter -- Peter Williams pwil3058@bigpond.net.au
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