linux-kernel - Re: [PATCH] sched: balance_cpu to consider other cpus in its group as target of (pinned) task migration

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Message-ID: <20120604114130.GA3386@linux.vnet.ibm.com>
Date:	Mon, 4 Jun 2012 17:11:30 +0530
From:	Srivatsa Vaddagiri <vatsa@...ux.vnet.ibm.com>
To:	Peter Zijlstra <peterz@...radead.org>
Cc:	Prashanth Nageshappa <prashanth@...ux.vnet.ibm.com>,
	mingo@...nel.org, LKML <linux-kernel@...r.kernel.org>,
	roland@...nel.org, efault@....de, Ingo Molnar <mingo@...e.hu>
Subject: Re: [PATCH] sched: balance_cpu to consider other cpus in its group
 as target of (pinned) task migration

* Peter Zijlstra <peterz@...radead.org> [2012-06-04 11:00:54]:

> > Signed-off-by: Srivatsa Vaddagiri <vatsa@...ux.vnet.ibm.com>
> 
> Did vatsa write this patch?

I wrote the first version of the patch which Prashanth took, tested,
fixed a bug and is finally publishing it. So yes,

> If so, you forgot a From header, if not, wtf!?

it is missing the From header.

> OK, so previously we only pulled to ourselves,

That't not entirely true isn't it i.e this_cpu need not equal
smp_processor_id even before this change.

> now you make cpu x move
> from cpu y to cpu z. This changes the dynamic of the load-balancer, not
> a single word on that and its impact/ramifications.

The other possibility is for the right sibling cpus to do load balance
in the same domain (noting that it needs to pull a task from another
sched_group to itself and ignoring balance_cpu). That seemed like a more
invasive change than this patch. We'd be happy to try any other approach
you have in mind.

- vatsa

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