Re: [Patch] don't kick ALB in the presence of pinned task

[Ingo Molnar]

* Siddha, Suresh B <suresh.b.siddha@xxxxxxxxx> wrote:

> Jack Steiner brought this issue at my OLS talk.
> 
> Take a scenario where two tasks are pinned to two HT threads in a physical
> package. Idle packages in the system will keep kicking migration_thread
> on the busy package with out any success.
> 
> We will run into similar scenarios in the presence of CMP/NUMA.
> 
> Patch appended.
> 
> Signed-off-by: Suresh Siddha <suresh.b.siddha@xxxxxxxxx>

nice catch!

fine for -mm, but i dont think we need this fix in 2.6.13, as the effect 
of the bug is an extra context-switch per 'CPU goes idle' event, in this 
very specific (and arguably broken) task binding scenario. In a 
worst-case scenario a CPU going idle can 'spam' that other CPU with 
migration requests, but it still seems like a pretty artificial workload 
scenario where the system has significant idle time left. I have tested 
your fix on a HT box and it solves the problem.

Acked-by: Ingo Molnar <mingo@xxxxxxx>

	Ingo
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