Messages in this thread | | | Subject | Re: [ANNOUNCE] BLD-3.17 release. | From | Mike Galbraith <> | Date | Mon, 13 Oct 2014 20:07:02 +0200 |
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On Mon, 2014-10-13 at 21:14 +0600, Rakib Mullick wrote:
> Okay. From the numbers above it's apparent that BLD isn't doing good, > atleast for the > kind of system that you have been using. I didn't had a chance to ran > it on any kind of > NUMA systems, for that reason on Kconfig, I've marked it as "Not > suitable for NUMA", yet.
(yeah, a NUMA box would rip itself to shreds)
> Part of the reason is, I didn't manage to try it out myself and other > reason is, it's easy to > get things wrong if schedule domains are build improperly. I'm not > sure what was the > sched configuration in your case. BLD assumes (or kindof bliendly > believes systems > default sched domain topology) on wakeup tasks are cache hot and so > don't put those > task's on other sched domains, but if that isn't the case then perhaps > it'll miss out on > balancing oppourtunity, in that case CPU utilization will be improper.
Even when you have only one socket with a big L3, you don't really want to bounce fast/light tasks around too frequently, L2 misses still hurt.
> Can you please share the perf stat of netperf runs? So, far I have > seen reduced context > switch numbers with -BLD with a drawback of huge increase of CPU > migration numbers.
No need, it's L2 misses. Q6600 has no L3 to mitigate the miss pain.
> But, the kind of systems I ran so far, it deemed too much CPU movement > didn't cost much. > But, it could be wrong for NUMA systems.
You can most definitely move even very fast/light tasks too much within an L3, L2 misses can demolish throughput. We had that problem.
-Mike
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