Subject: Re: VolanoMark regression with 2.6.27-rc1
From: "Zhang, Yanmin" <yanmin_zhang@linux.intel.com>
To: Dhaval Giani <dhaval@linux.vnet.ibm.com>,
       LKML <linux-kernel@vger.kernel.org>
Cc: Peter Zijlstra <a.p.zijlstra@chello.nl>, Ingo Molnar <mingo@elte.hu>,
       Srivatsa Vaddagiri <vatsa@linux.vnet.ibm.com>,
       Aneesh Kumar KV <aneesh.kumar@linux.vnet.ibm.com>,
       Balbir Singh <balbir@in.ibm.com>
In-Reply-To: <20080818052155.GA5063@linux.vnet.ibm.com>
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	 <1912217169.25608.228.camel@ymzhang> <1218180605.8625.64.camel@twins>
	 <20080811185008.GA29291@linux.vnet.ibm.com>
	 <1912726331.25608.235.camel@ymzhang>
	 <20080817115035.GA32223@linux.vnet.ibm.com>
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Date: Wed, 20 Aug 2008 15:24:49 +0800
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On Mon, 2008-08-18 at 10:51 +0530, Dhaval Giani wrote: 
> > > > > > So with kernel 2.6.27-rc1, the successful wakeup_affine is about
> > > > > > double of the one of 2.6.27-rc1
> > > > > > on domain 0, but about 10 times on domain 1. That means more tasks are
> > > > > > woken up on waker cpus.
> > > > > > 
> > > > > > Does that mean it doesn't follow cache-hot checking?
> > > > > 
> > > > > I'm a bit puzzled, but you're right - I too noticed that volanomark is
> > > > > _very_ sensitive to affine wakeups.
> > > > > 
> > > > > I'll try and find what changed in that code for GROUP=n.
> > > > 
> > > > hi Yanmin,
> > > > 
> > > > I was wondering if you could send me your config and what sysctls you
> > > > have set. I have not been able to reproduce the 2.6.26 -> 2.6.27-rc1
> > > > GROUP=n regression.
> > > Pls. see the attachment. As for sysctl, I just set /proc/sys/kernel/sched_compat_yield=1.
> > > 
> > > I am wondering if the load balance causes the regression when group=n. I manually delete
> > > all GROUP codes and do a diff against 26 and 27-rc1.
> > > 
> > 
> > You can disable load balancing by being in uniprocessor mode.
> > 
> 
> Hi,
> 
> I can see this regression only with sched_compat_yield=1. Some numbers
> though, I see a 5% regression with max_cpus=1 whereas close to 50% with
> SMP on a 8 way.
After reverting below patch, volanoMark regression becomes less than 2% with CONFIG_GROUP_SCHED=n
on my 8-core stoakely. The improvement on 16-core tigerton is about 44%, but there is still about
 20% regression, comparing with 2.6.26_nogroup.


commit 93b75217df39e6d75889cc6f8050343286aff4a5
Author: Peter Zijlstra <a.p.zijlstra@chello.nl>
Date:   Fri Jun 27 13:41:33 2008 +0200

    sched: disable source/target_load bias
    
    The bias given by source/target_load functions can be very large, disable
    it by default to get faster convergence.
    
    Signed-off-by: Peter Zijlstra <peterz@infradead.org>
    Cc: Srivatsa Vaddagiri <vatsa@linux.vnet.ibm.com>
    Cc: Mike Galbraith <efault@gmx.de>
    Signed-off-by: Ingo Molnar <mingo@elte.hu>


This patch adds a new feature LB_BIAS, but uses it with a NOT, so I lost it when I tested
single sched feature one by one. That also explains why wake_affine and load_balance_newidle
have more successful task pulling with kernel 2.6.27-rc, because MC and CPU domain's wake_idx
is 1, so this patch has impact on them.

Dhaval, could you test it on your 8-way machine?

> 
> Peter do you have any patches already, which I can try?
> 
> Thanks,

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