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

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Date:	Thu, 06 Dec 2007 11:29:27 -0500
From:	Jie Chen <chen@...b.org>
To:	Ingo Molnar <mingo@...e.hu>
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

Ingo Molnar wrote:
> * 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,\
Hi, Ingo:

I did patch the header file and recompiled the kernel. I observed no 
difference (two threads overhead stays too high). Thank you.

-- 
###############################################
Jie Chen
Scientific Computing Group
Thomas Jefferson National Accelerator Facility
12000, Jefferson Ave.
Newport News, VA 23606

(757)269-5046 (office) (757)269-6248 (fax)
chen@...b.org
###############################################

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