Message-ID: <1338820895.7356.252.camel@marge.simpson.net>
Subject: Re: [PATCH] sched: balance_cpu to consider other cpus in its group
 as target of (pinned) task migration
From: Mike Galbraith <efault@gmx.de>
To: Srivatsa Vaddagiri <vatsa@linux.vnet.ibm.com>
Cc: Peter Zijlstra <peterz@infradead.org>,
        Prashanth Nageshappa <prashanth@linux.vnet.ibm.com>, mingo@kernel.org,
        LKML <linux-kernel@vger.kernel.org>, roland@kernel.org,
        Ingo Molnar <mingo@elte.hu>
Date: Mon, 04 Jun 2012 16:41:35 +0200
In-Reply-To: <20120604143802.GB26651@linux.vnet.ibm.com>
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On Mon, 2012-06-04 at 20:08 +0530, Srivatsa Vaddagiri wrote: 
> * Mike Galbraith <efault@gmx.de> [2012-06-04 16:30:34]:
> 
> > Yeah, this is true, it is a latency source and a fairness violation.
> > Slow path balance consideration does make some sense to me.
> > 
> > But, if you have an RT requirement, you can't afford to mix unknown
> > entities, nor over-commit etc.  A realtime application will assign all
> > resources, so the load balancer becomes essentially unemployed.  No?
> > Non critical worker-bees may be allowed to bounce around in say a
> > cpuset, but none of the CPUs which do critical work will ever be
> > over-committed, else application just lost the war.  In that regard,
> > twiddling the load balancer to accommodate strange sounding case still
> > seems wrong to me.
> 
> Btw the patch should help non-rt case as well (where a high
> priority SCHED_OTHER is hogging cpu while low-priority SCHED_OTHER task
> on that same cpu suffers as we choose not to move it to another
> cpu (because of the way balance_cpu based load balance is written).

But high priority SCHED_OTHER tasks do not hog the CPU, they get their
fair share as defined by the user.

-Mike

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