From: Con Kolivas <kernel@kolivas.org>
To: ray-gmail@madrabbit.org
Cc: "Siddha, Suresh B" <suresh.b.siddha@intel.com>,
"linux kernel mailing list" <linux-kernel@vger.kernel.org>,
"ck list" <ck@vds.kolivas.org>
Subject: Re: RSDL v0.30 cpu scheduler for mainline kernels
Date: Fri, 16 Mar 2007 08:11:50 +1100 [thread overview]
Message-ID: <200703160811.51088.kernel@kolivas.org> (raw)
In-Reply-To: <2c0942db0703151158l59cbede2x845fc134d9f1cf9d@mail.gmail.com>
On Friday 16 March 2007 05:58, Ray Lee wrote:
> On 3/15/07, Siddha, Suresh B <suresh.b.siddha@intel.com> wrote:
> > On Thu, Mar 15, 2007 at 05:05:13PM +1100, Con Kolivas wrote:
> > > On Thursday 15 March 2007 13:31, Siddha, Suresh B wrote:
> > > > Just to see the % increase in number of context switches, I ran 8
> > > > infinite loops (simple while(1); 's) and with 2.6.21-rc3 I see ~70
> > > > context switches every second, whereas with RSDL I see ~530 context
> > > > switches.
> > >
> > > Thanks. If it's just that then scaling rr interval with cpus somewhat
> > > would help. If you could, the following patch just to test might
> > > confirm that. -#define RR_INTERVAL ((6 * HZ / 1001) + 1)
> > > +#define RR_INTERVAL ((12 * HZ / 1001) + 1)
> >
> > Context switches now are ~370 per second. Still much above the regular
> > ~70 we see in the mainline.
> >
> > why do you say the rr_interval needs to be scaled with cpus? The basic
> > point in RSDL is, if we have more than one same priority task on a single
> > logic cpu, context switch happens every RR_INTERVAL (6 or 12 msec)
> > whereas in mainline it happens every 100 msec.
No. That's what we do with mainline too. The analogue of the RR_INTERVAL in
mainline is the timeslice granularity. When I wrote it (TG) I assumed that
any increase in latency by lengthening this value would be offset by more
cpus being available which is only partially true. I also did not assume at
the time that many cpus would be used on a desktop which is now, wrong.
> With more CPUs, the context switch period can be multiplied by that
> number of CPUs while still allowing all tasks the same frequency of
> access to the CPU. With 4 processors, the context switch would be
> 24ms, by which point we're probably reaching the point of diminishing
> returns for minimizing overhead and maximizing throughput.
>
> > We need to minimize these context switches.
>
> That's a judgement call. If a synthetic benchmark degrades but other
> things improve, then this, as most everything in computer science, is
> yet another trade-off that needs to be evaluated. (You recognize there
> is a tradeoff here, right? Some benchmarks would improve even further
> if the switch time were 500ms. But that would make the system nearly
> unusable in general.)
>
> Ray
--
-ck
next prev parent reply other threads:[~2007-03-15 21:12 UTC|newest]
Thread overview: 20+ messages / expand[flat|nested] mbox.gz Atom feed top
2007-03-11 23:58 RSDL v0.30 cpu scheduler for mainline kernels Con Kolivas
2007-03-12 23:46 ` David Miller
2007-03-13 3:05 ` Con Kolivas
2007-03-13 4:32 ` Willy Tarreau
2007-03-13 5:03 ` [ck] " Felipe Alfaro Solana
2007-03-13 5:29 ` David Miller
2007-03-13 13:10 ` [ck] " michael chang
2007-03-13 15:35 ` [ck] " Ash Milsted
2007-03-13 15:46 ` Con Kolivas
2007-03-13 15:53 ` Lee Revell
2007-03-13 17:45 ` Chris Friesen
2007-03-13 20:02 ` Lee Revell
2007-03-14 9:47 ` Ash Milsted
2007-03-15 2:31 ` Siddha, Suresh B
2007-03-15 6:05 ` Con Kolivas
2007-03-15 17:46 ` Siddha, Suresh B
2007-03-15 18:58 ` Ray Lee
2007-03-15 21:11 ` Con Kolivas [this message]
2007-03-15 21:12 ` Siddha, Suresh B
2007-03-17 14:27 ` Szonyi Calin
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