linux-kernel - Re: [PATCH v3] sched: balance_cpu to consider other cpus in its group as target of (pinned) task

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Message-ID: <1340213901.21745.122.camel@twins>
Date:	Wed, 20 Jun 2012 19:38:21 +0200
From:	Peter Zijlstra <peterz@...radead.org>
To:	Prashanth Nageshappa <prashanth@...ux.vnet.ibm.com>
Cc:	mingo@...nel.org, LKML <linux-kernel@...r.kernel.org>,
	roland@...nel.org, Srivatsa Vaddagiri <vatsa@...ux.vnet.ibm.com>,
	efault@....de, Ingo Molnar <mingo@...e.hu>
Subject: Re: [PATCH v3] sched: balance_cpu to consider other cpus in its
 group as target of (pinned) task

On Tue, 2012-06-19 at 17:43 +0530, Prashanth Nageshappa wrote:
> T2 will starve eternally in this case. The same
> scenario can arise in presence of non-rt tasks as well (say we replace F1 with
> high irq load or with a very high priority SCHED_OTHER task that can't move out
> of C2). 

Uhm, no. In the case where both F1 and T2 are SCHED_OTHER starvation is
impossible.

What can happen with pure SCHED_OTHER affinities is being less fair than
desired.

Anyway, I took the patch with a few minor edits -- ie. we don't need to
reset loop_break, its never changed (same for the ALL_PINNED patch you
sent).


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