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

From: Ingo Molnar (mingo_at_elte.hu)
Date: 08/02/05

  • Next message: Ingo Molnar: "Re: [Patch] don't kick ALB in the presence of pinned task" 
    Date:	Tue, 2 Aug 2005 11:27:17 +0200
To: "Siddha, Suresh B" <suresh.b.siddha@intel.com>

    * Siddha, Suresh B <suresh.b.siddha@intel.com> 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@intel.com>

    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@elte.hu>

            Ingo
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