Messages in this thread | | | Date | Tue, 14 Oct 2014 21:06:31 +0600 | Subject | Re: [ANNOUNCE] BLD-3.17 release. | From | Rakib Mullick <> |
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On 10/14/14, Mike Galbraith <umgwanakikbuti@gmail.com> wrote: > 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. > I see.
>> 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. > So, L2 misses is the key here. So far I haven't tried to utilize various sched domain flags, like. SD_SHARE_PKG_RESOURCE/_CPUPOWER etc. Probably, integrating those might help? I'll take a look at those and will try to see what happens, although testing will be problematic.
Thanks, Rakib.
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