Re: [PATCH 3/5] irq_work: Implement remote queueing

From: Frederic Weisbecker
Date: Tue Jun 03 2014 - 11:08:30 EST


On Tue, Jun 03, 2014 at 05:00:08PM +0200, Peter Zijlstra wrote:
> On Tue, Jun 03, 2014 at 04:40:18PM +0200, Frederic Weisbecker wrote:
> > irq work currently only supports local callbacks. However its code
> > is mostly ready to run remote callbacks and we have some potential user.
> >
> > The full nohz subsystem currently open codes its own remote irq work
> > on top of the scheduler ipi when it wants a CPU to reevaluate its next
> > tick. However this ad hoc solution bloats the scheduler IPI.
> >
> > Lets just extend the irq work subsystem to support remote queuing on top
> > of the generic SMP IPI to handle this kind of user. This shouldn't add
> > noticeable overhead.
> >
> > Suggested-by: Peter Zijlstra <peterz@xxxxxxxxxxxxx>
> > Cc: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
> > Cc: Ingo Molnar <mingo@xxxxxxxxxx>
> > Cc: Kevin Hilman <khilman@xxxxxxxxxx>
> > Cc: Paul E. McKenney <paulmck@xxxxxxxxxxxxxxxxxx>
>
> Acked-by: Peter Zijlstra <peterz@xxxxxxxxxxxxx>
>
> > Cc: Thomas Gleixner <tglx@xxxxxxxxxxxxx>
> > Cc: Viresh Kumar <viresh.kumar@xxxxxxxxxx>
> > Signed-off-by: Frederic Weisbecker <fweisbec@xxxxxxxxx>
> > ---
> > include/linux/irq_work.h | 2 ++
> > kernel/irq_work.c | 22 +++++++++++++++++++++-
> > kernel/smp.c | 4 ++++
> > 3 files changed, 27 insertions(+), 1 deletion(-)
>
> > @@ -198,6 +199,9 @@ void generic_smp_call_function_single_interrupt(void)
> > csd->func(csd->info);
> > csd_unlock(csd);
> > }
> > +
> > + /* Handle irq works queued remotely by irq_work_queue_on() */
> > + irq_work_run();
> > }
>
> One could possibly extend that comment by stating that we explicitly run
> the irq_work bits after the function bits, because the function bits are
> typically synchronous and have people waiting on them, while not so for
> the irq_works.
>

Good point! I'll expand the comment.
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