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    SubjectRe: [patch 1/4] sched: Separate the scheduler entry for preemption
    On Wed, 22 Jun 2011, Christoph Hellwig wrote:

    > On Wed, Jun 22, 2011 at 05:52:13PM -0000, Thomas Gleixner wrote:
    > > Block-IO and workqueues call into notifier functions from the
    > > scheduler core code with interrupts and preemption disabled. These
    > > calls should be made before entering the scheduler core.
    > >
    > > To simplify this, separate the scheduler core code into
    > > __schedule(). __schedule() is directly called from the places which
    > > set PREEMPT_ACTIVE and from schedule(). This allows us to add the work
    > > checks into schedule(), so they are only called when a task voluntary
    > > goes to sleep.
    > I don't think that works. We'll need to flush the block requests even
    > for an involuntary schedule.

    We don't do that right now as that code conditional on:

    if (prev->state && !(preempt_count() & PREEMPT_ACTIVE)) {

    Also blk_flush_plug_list() when called from io_schedule() is
    preemptible, so you might be preempted in the middle of the list
    operations, so calling into it when preempted would result in an utter



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