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SubjectRe: HT (Hyper Threading) aware process scheduling doesn't work as it should
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On Mon, 31 Oct 2011 12:42:28 PM Mike Galbraith wrote:
> On Mon, 2011-10-31 at 21:06 +1100, Con Kolivas wrote:
> > On Sun, 30 Oct 2011 07:57:12 PM Artem S. Tashkinov wrote:
> > > I've found out that even on Linux 3.0.8 the process scheduler
> > > doesn't
> > > correctly distributes the load amongst virtual CPUs. E.g. on a
> > > 4-core
> > > system (8 total virtual CPUs) the process scheduler often run some
> > > instances of four different tasks on the same physical CPU.
> > >
> > > Any thoughts? comments? I think this is quite a serious problem.
> >
> > Intense cache locality logic, power saving concepts, cpu frequency
> > governor behaviour and separate runqueues per CPU within the current
> > CPU process scheduler in the current mainline linux kernel will
> > ocasionally do this. Some workloads will be better, while others will
> > be worse. Feel free to try my BFS cpu scheduler if you wish a CPU
> > process scheduler that spreads work more evenly across CPUs.
> >
> > Alas the last version I synced up with will not apply cleanly past about
> > 3.0.6 I believe:
> >
> > http://ck.kolivas.org/patches/bfs/3.0.0/3.0-sched-bfs-413.patch
>
> Yeah, it handles independent tasks well, but cache misses can be
> excruciatingly painful for the others.
>
> Q6600 box, configs as identical as possible, tbench 8
>
> 3.0.6-bfs413 728.6 MB/sec
> 3.0.8 1146.7 MB/sec
>
> -Mike

Fortunately BFS is about optimising user visible service latency for normal
users running normal applications on normal desktops under normal workloads,
and not about tbench throughput.

Regards,
Con
--
-ck


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