linux-kernel - [RFC] Cpuset: remove useless sched domain line

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Date:	Fri, 13 Oct 2006 21:55:17 -0700
From:	Paul Jackson <pj@....com>
To:	Dinakar Guniguntala <dino@...ibm.com>
Cc:	Simon.Derr@...l.net, Paul Jackson <pj@....com>,
	linux-kernel@...r.kernel.org
Subject: [RFC] Cpuset: remove useless sched domain line

Dinakar,

(1) Does this patch look right to you?

(2) I don't understand this code:

      * When do we ever create sched domains for cpusets
        that -are- cpu_exclusive?  All I see here are
	calls to partition_sched_domains() with various
	permutations of pspan and cspan that are the
	cpus from various non-exclusive cpusets.

      * Why do we return (setting up no sched domains
	at this time) if the current cpuset's cpus
	covers all the non exclusive cpus of our parent,
	but continue on to make a sched domain just for
	our parent if there are other non-exclusive cpus
	in our sibling cpusets?

====

Remove a useless line from the sched domain setup code in cpusets.

When I removed the 'is_removed()' flag test from the sched domain
setup code in cpusets, as part of my July 23, 2006 patch:

    Cpuset: fix ABBA deadlock with cpu hotplug lock

I failed to notice that this opened the door to a little bit of code
simplification.  A line of code that had to cover for the possibility
that a cpuset marked cpu_exclusive was marked for removal could
be eliminated.  In the code section visible in this patch, it is
now the case that cur->cpus_allowed is always a subset of pspan,
so it is always a no-op to cpus_or() cur->cpus_allowed into pspan.

Signed-off-by: Paul Jackson <pj@....com>

---

 kernel/cpuset.c |    1 -
 1 files changed, 1 deletion(-)

--- 2.6.19-rc1-mm1.orig/kernel/cpuset.c	2006-10-13 21:31:16.000000000 -0700
+++ 2.6.19-rc1-mm1/kernel/cpuset.c	2006-10-13 21:32:20.000000000 -0700
@@ -783,7 +783,6 @@ static void update_cpu_domains(struct cp
 			cpus_andnot(pspan, pspan, c->cpus_allowed);
 	}
 	if (!is_cpu_exclusive(cur)) {
-		cpus_or(pspan, pspan, cur->cpus_allowed);
 		if (cpus_equal(pspan, cur->cpus_allowed))
 			return;
 		cspan = CPU_MASK_NONE;

-- 
                  I won't rest till it's the best ...
                  Programmer, Linux Scalability
                  Paul Jackson <pj@....com> 1.925.600.0401
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