linux-kernel - Re: Possible bug from kernel 2.6.22 and above, 2.6.24-rc4

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Date:	Thu, 6 Dec 2007 11:43:18 +0100
From:	Ingo Molnar <mingo@...e.hu>
To:	Jie Chen <chen@...b.org>
Cc:	Simon Holm Th??gersen <odie@...aau.dk>,
	Eric Dumazet <dada1@...mosbay.com>,
	linux-kernel@...r.kernel.org,
	Peter Zijlstra <a.p.zijlstra@...llo.nl>
Subject: Re: Possible bug from kernel 2.6.22 and above, 2.6.24-rc4


* Jie Chen <chen@...b.org> wrote:

>> not "BARRIER time". I've re-read the discussion and found no hint 
>> about how to build and run a barrier test. Either i missed it or it's 
>> so obvious to you that you didnt mention it :-)
>>
>> 	Ingo
>
> Hi, Ingo:
>
> Did you do configure --enable-public-release? My qmt is for qcd 
> calculation (one type of physics code) [...]

yes, i did exactly as instructed.

> [...]. Without the above flag one can only test PARALLEL overhead. 
> Actually the PARALLEL benchmark has the same behavior as the BARRIER. 
> Thanks.

hm, but PARALLEL does not seem to do that much context switching. So 
basically you create the threads and do a few short runs to establish 
overhead? Threads do not get fork-balanced at the moment - but turning 
it on would be easy. Could you try the patch below - how does it impact 
your results? (and please keep affinity setting off)

	Ingo

----------->
Subject: sched: reactivate fork balancing
From: Ingo Molnar <mingo@...e.hu>

reactivate fork balancing.

Signed-off-by: Ingo Molnar <mingo@...e.hu>
---
 include/linux/topology.h |    3 +++
 1 file changed, 3 insertions(+)

Index: linux/include/linux/topology.h
===================================================================
--- linux.orig/include/linux/topology.h
+++ linux/include/linux/topology.h
@@ -103,6 +103,7 @@
 	.forkexec_idx		= 0,			\
 	.flags			= SD_LOAD_BALANCE	\
 				| SD_BALANCE_NEWIDLE	\
+				| SD_BALANCE_FORK	\
 				| SD_BALANCE_EXEC	\
 				| SD_WAKE_AFFINE	\
 				| SD_WAKE_IDLE		\
@@ -134,6 +135,7 @@
 	.forkexec_idx		= 1,			\
 	.flags			= SD_LOAD_BALANCE	\
 				| SD_BALANCE_NEWIDLE	\
+				| SD_BALANCE_FORK	\
 				| SD_BALANCE_EXEC	\
 				| SD_WAKE_AFFINE	\
 				| SD_WAKE_IDLE		\
@@ -165,6 +167,7 @@
 	.forkexec_idx		= 1,			\
 	.flags			= SD_LOAD_BALANCE	\
 				| SD_BALANCE_NEWIDLE	\
+				| SD_BALANCE_FORK	\
 				| SD_BALANCE_EXEC	\
 				| SD_WAKE_AFFINE	\
 				| BALANCE_FOR_PKG_POWER,\
--
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