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    SubjectRe: [PATCH -rt 2/5] Thread Migration Preemption - v2
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    On Sat, 2007-07-14 at 21:16 +0400, Oleg Nesterov wrote:
    > On 07/14, Peter Zijlstra wrote:
    > >
    > > From: Mathieu Desnoyers <mathieu.desnoyers@polymtl.ca>
    > >
    > > This patch adds the ability to protect critical sections from migration to
    > > another CPU without disabling preemption.
    > >
    > > This will be useful to minimize the amount of preemption disabling for the -rt
    > > patch. It will help leveraging improvements brought by the local_t types in
    > > asm/local.h (see Documentation/local_ops.txt). Note that the updates done to
    > > variables protected by migrate_disable must be either atomic or protected from
    > > concurrent updates done by other threads.
    > >
    > > Typical use:
    > >
    > > migrate_disable();
    > > local_inc(&__get_cpu_var(&my_local_t_var));
    > > migrate_enable();
    > >
    > > Which will increment the variable atomically wrt the local CPU.
    >
    > I still think this patch is buggy. Perhaps I am wrong. Please look at
    >
    > http://marc.info/?l=linux-kernel&m=118417177818825
    >
    > there was no any reply.

    Looking at it, I tend to agree that the migration_thread thing is indeed
    quite broken. Not quite sure on how to solve it nicely though, one would
    need to stick the migration request structure somewhere in task_struct
    or thread_info, and not back on the migration_queue. But given that
    people already complained about the adding ov migration_counter,. I'm
    not daring to propose such things.


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