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

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Message-ID: <20070315174654.GB12447@linux-os.sc.intel.com>
Date:	Thu, 15 Mar 2007 10:46:54 -0700
From:	"Siddha, Suresh B" <suresh.b.siddha@...el.com>
To:	Con Kolivas <kernel@...ivas.org>
Cc:	"Siddha, Suresh B" <suresh.b.siddha@...el.com>,
	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 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.

We need to minimize these context switches.

thanks,
suresh
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