Re: [PATCH] SMT Nice 2.6.4-rc1-mm1

From: Con Kolivas
Date: Mon Mar 01 2004 - 06:56:34 EST


On Mon, 1 Mar 2004 10:40 pm, Con Kolivas wrote:
> On Mon, 1 Mar 2004 10:37 pm, Nick Piggin wrote:
> > Con Kolivas wrote:
> > >On Mon, 1 Mar 2004 05:52 pm, Con Kolivas wrote:
> > >>This patch provides full per-package priority support for SMT
> > >> processors (aka pentium4 hyperthreading) when combined with
> > >> CONFIG_SCHED_SMT.
> > >
> > >And here are some benchmarks to demonstrate what happens.
> > >P4 3.06Ghz booted with bios HT off as UP (up), SMP with mm1(mm1), SMP
> > > with mm1-smtnice(sn)
> >
> > Pretty impressive numbers.
> >
> > How does it go on the desktop when running mprime at nice +19?
> > How much worse can latencies of the niced tasks become? Any idea?
>
> Worst case scenario is easy to model; if a nice -19 task starts at exactly
> the same time as a nice +19 task, the timeslices are 200 and 10ms. On
> uniprocessor the nice+19 task will wait _at least_ 200 ms. On SMT nice SMP
> it will be 200 - (200 * 15 / 100) so 170ms. That is of course worst case
> scenario and still better than UP since the latency will be less, the task
> will definitely start (interactive reinsertion wont affect it) and it will
> be on a second runqueue.

Ok if you're having trouble with working that out it's because it's wrong
goddamn it. It's when the timeslice of the high priority task drops to 10 *
100 / 85 so when it drops to 12ms. ie 188 ms latency.

Con
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