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    SubjectRe: [Patch] restore the RCU callback to defer put_task_struct() Re: Problems with 2.6.17-rt8


    On Thu, 10 Aug 2006, Bill Huey wrote:

    > On Wed, Aug 09, 2006 at 07:18:35PM -0700, Bill Huey wrote:
    >> On Thu, Aug 10, 2006 at 12:05:57AM +0200, Esben Nielsen wrote:
    >>> I had a long discussion with Paul McKenney about this. I opposed the patch
    >>> from a latency point of view: Suddenly a high-priority RT task could be
    >>> made into releasing a task_struct. It would be better for latencies to
    >>> defer it to a low priority task.
    >>>
    >>> The conclusion we ended up with was that it is not a job for the RCU
    >>> system, but it ought to be deferred to some other low priority task to
    >>> free the task_struct.
    >>
    >> I agree. It's just hack to get it not to crash at this time. It really
    >> should be done in another facility or utilizing another threading context.
    >
    > Esben and company,
    >
    > This is the second round of getting rid of the locking problems with free_task()
    >
    > This extends the mmdrop logic with desched_thread() to also handle free_task()
    > requests as well. I believe this address your concerns and I'm open to review
    > of this patch.
    >
    > Patch included:
    >
    > bill
    >
    >
    Without applying the patch and only skimming it it looks like what Paul
    and I concluded :-)

    But is there really no generic way of defering this kind of thing? It
    looks like a hell of a lot work where a kind of "message" infrastructure
    could have solved it in a few lines.

    Esben
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