linux-kernel - [PATCH] x86, sched: fix up typo in topology detection

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Message-Id: <20140930214546.FD481CFF@viggo.jf.intel.com>
Date:	Tue, 30 Sep 2014 14:45:46 -0700
From:	Dave Hansen <dave@...1.net>
To:	linux-kernel@...r.kernel.org
Cc:	Dave Hansen <dave@...1.net>, dave.hansen@...ux.intel.com,
	akpm@...ux-foundation.org, peterz@...radead.org, mingo@...nel.org
Subject: [PATCH] x86, sched: fix up typo in topology detection


From: Dave Hansen <dave.hansen@...ux.intel.com>

Commit cebf15eb09 (in linux-next now) added some code to try to
detect the situation where we have a NUMA node inside of the
"DIE" sched domain.  It detected this by looking for cpus which
match_die() but do not match NUMA nodes via topology_same_node().

I wrote it up as:

	if (match_die(c, o) == !topology_same_node(c, o))

which actually seemed to work some of the time, albiet
accidentally.

It should have been doing an &&, not an ==.

This code essentially chopped off the "DIE" domain on one of
Andrew Morton's systems.  He reported that this patch fixed his
issue.

Signed-off-by: Dave Hansen <dave.hansen@...ux.intel.com>
Reported-by: Andrew Morton <akpm@...ux-foundation.org>
Cc: Peter Zijlstra <peterz@...radead.org>
Cc: Ingo Molnar <mingo@...nel.org>
---

 b/arch/x86/kernel/smpboot.c |    2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff -puN arch/x86/kernel/smpboot.c~fix-up-typo arch/x86/kernel/smpboot.c
--- a/arch/x86/kernel/smpboot.c~fix-up-typo	2014-09-30 14:24:52.934235516 -0700
+++ b/arch/x86/kernel/smpboot.c	2014-09-30 14:30:42.074917876 -0700
@@ -445,7 +445,7 @@ void set_cpu_sibling_map(int cpu)
 			} else if (i != cpu && !c->booted_cores)
 				c->booted_cores = cpu_data(i).booted_cores;
 		}
-		if (match_die(c, o) == !topology_same_node(c, o))
+		if (match_die(c, o) && !topology_same_node(c, o))
 			primarily_use_numa_for_topology();
 	}
 }
_
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