linux-kernel - Re: HT (Hyper Threading) aware process scheduling doesn't work as it should

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Date:	Mon, 31 Oct 2011 12:42:28 +0100
From:	Mike Galbraith <efault@....de>
To:	Con Kolivas <con@...ivas.org>
Cc:	"Artem S. Tashkinov" <t.artem@...os.com>,
	linux-kernel@...r.kernel.org
Subject: Re: HT (Hyper Threading) aware process scheduling doesn't work as
 it should

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

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