Message-ID: <442722C4.4030409@bigpond.net.au>
Date: Mon, 27 Mar 2006 10:24:52 +1100
From: Peter Williams <pwil3058@bigpond.net.au>
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To: "Siddha, Suresh B" <suresh.b.siddha@intel.com>
CC: Andrew Morton <akpm@osdl.org>, Ingo Molnar <mingo@elte.hu>,
       Nick Piggin <nickpiggin@yahoo.com.au>, Con Kolivas <kernel@kolivas.org>,
       "Chen, Kenneth W" <kenneth.w.chen@intel.com>,
       Mike Galbraith <efault@gmx.de>, linux-kernel@vger.kernel.org
Subject: Re: more smpnice patch issues
References: <20060322155122.2745649f.akpm@osdl.org> <4421F702.5040609@bigpond.net.au> <20060324154558.A20018@unix-os.sc.intel.com>
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Siddha, Suresh B wrote:
> more issues with smpnice patch...
> 
> a) consider a 4-way system (simple SMP system with no HT and cores) scenario
> where a high priority task (nice -20) is running on P0 and two normal
> priority tasks running on P1. load balance with smp nice code
> will never be able to detect an imbalance and hence will never move one of 
> the normal priority tasks on P1 to idle cpus P2 or P3.

Fix already sent.

> 
> b) smpnice seems to break this patch..
> 
> [PATCH] sched: allow the load to grow upto its cpu_power
> http://www.kernel.org/git/?p=linux/kernel/git/torvalds/linux-2.6.git;a=commitdiff;h=0c117f1b4d14380baeed9c883f765ee023da8761
> 
> example scenario for this case: consider a numa system with two nodes, each
> node containing four processors. if there are two processes in node-0 and with
> node-1 being completely idle, your patch will move one of those processes to
> node-1 whereas the previous behavior will retain those two processes in node-0..
> (in this case, in your code max_load will be less than busiest_load_per_task)

I think that the patch I sent to address a) above will also fix this 
problem as find_busiest_queue() will no longer find node-0 as the 
busiest group unless both of the processes in node-0 are on the same 
CPU.  This is because it now only considers groups that have at least 
one CPU with more than one running task as candidates for being the 
busiest group.

Implicit in this is the assumption that it's OK to move one of the tasks 
from node-0 to node-1 if they're both on the same CPU within node-0.

Could you confirm this is OK?

Thanks,
Peter
-- 
Peter Williams                                   pwil3058@bigpond.net.au

"Learning, n. The kind of ignorance distinguishing the studious."
  -- Ambrose Bierce
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