linux-kernel - Re: RSDL v0.30 cpu scheduler for mainline kernels

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Date:	Thu, 15 Mar 2007 17:05:13 +1100
From:	Con Kolivas <kernel@...ivas.org>
To:	"Siddha, Suresh B" <suresh.b.siddha@...el.com>
Cc:	linux kernel mailing list <linux-kernel@...r.kernel.org>,
	ck list <ck@....kolivas.org>
Subject: Re: RSDL v0.30 cpu scheduler for mainline kernels

On Thursday 15 March 2007 13:31, Siddha, Suresh B wrote:
> Con,
>
> On Mon, Mar 12, 2007 at 10:58:11AM +1100, Con Kolivas wrote:
> > There are updated patches for 2.6.20, 2.6.20.2, 2.6.21-rc3 and
> > 2.6.21-rc3-mm2 to bring RSDL up to version 0.30 for download here:
>
> I tried this on a Core 2 Quad cpu system(system has 4 cores on a single
> package). When I run SPECjbb2000 with number of threads varying from 1-8,
> I see ~4.5% perf regression with RSDL (compared to native 2.6.21-rc3) in
> the 8 threads case. This I think, is coming from increased number of
> context switches, when we have more than one thread(at same user priority)
> on the same logical cpu.
>
> 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.

---
 kernel/sched.c |    2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

Index: linux-2.6.21-rc3-mm2/kernel/sched.c
===================================================================
--- linux-2.6.21-rc3-mm2.orig/kernel/sched.c	2007-03-15 17:03:17.000000000 +1100
+++ linux-2.6.21-rc3-mm2/kernel/sched.c	2007-03-15 17:03:30.000000000 +1100
@@ -104,7 +104,7 @@ unsigned long long __attribute__((weak))
  * This is the time all tasks within the same priority round robin.
  * Set to a minimum of 6ms.
  */
-#define RR_INTERVAL		((6 * HZ / 1001) + 1)
+#define RR_INTERVAL		((12 * HZ / 1001) + 1)
 #define DEF_TIMESLICE		(RR_INTERVAL * 20)
 
 #ifdef CONFIG_SMP

-- 
-ck
-
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