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From: "Chen, Kenneth W" <kenneth.w.chen@intel.com>
To: "'Nick Piggin'" <nickpiggin@yahoo.com.au>,
       "Con Kolivas" <kernel@kolivas.org>
Cc: <linux-kernel@vger.kernel.org>, "'Chris Mason'" <mason@suse.com>,
       "Ingo Molnar" <mingo@elte.hu>
Subject: RE: [PATCH RFC] smt nice introduces significant lock contention
Date: Fri, 2 Jun 2006 01:38:34 -0700
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Nick Piggin wrote on Friday, June 02, 2006 12:53 AM
> Con Kolivas wrote:
> 
> >>Nice to acknowledge Chris's idea for 
> >>trylocks in your changelog when you submit a final patch.
> > 
> > 
> > I absolutely would and I would ask for him to sign off on it as well, once we 
> > agreed on a final form.
> 
> This is a small micro-optimisation / cleanup we can do after
> smtnice gets converted to use trylocks. Might result in a little
> less cacheline footprint in some cases.


Just to pile up more micro-optimization: kernel can break out of the
for_each_domain loop when it hits first SD_SHARE_CPUPOWER.

- Ken


Signed-off-by: Ken Chen <kenneth.w.chen@intel.com>


--- ./kernel/sched.c.orig	2006-06-01 23:14:47.000000000 -0700
+++ ./kernel/sched.c	2006-06-01 23:18:07.000000000 -0700
@@ -2780,8 +2780,10 @@ static int dependent_sleeper(int this_cp
 	int ret = 0, i;
 
 	for_each_domain(this_cpu, tmp)
-		if (tmp->flags & SD_SHARE_CPUPOWER)
+		if (tmp->flags & SD_SHARE_CPUPOWER) {
 			sd = tmp;
+			break;
+		}
 
 	if (!sd)
 		return 0;