Messages in this thread | | | Date | Wed, 22 Jun 2011 20:52:47 +0200 (CEST) | From | Thomas Gleixner <> | Subject | Re: [patch 1/4] sched: Separate the scheduler entry for preemption |
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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 disaster.
Thanks,
tglx
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