On Thu, Feb 17, 2022 at 1:48 AM Sebastian Andrzej Siewior <bigeasy@xxxxxxxxxxxxx> wrote: > > From: Michal Hocko <mhocko@xxxxxxxx> > > The optimisation is based on a micro benchmark where local_irq_save() is > more expensive than a preempt_disable(). There is no evidence that it is > visible in a real-world workload and there are CPUs where the opposite is > true (local_irq_save() is cheaper than preempt_disable()). > > Based on micro benchmarks, the optimisation makes sense on PREEMPT_NONE > where preempt_disable() is optimized away. There is no improvement with > PREEMPT_DYNAMIC since the preemption counter is always available. > > The optimization makes also the PREEMPT_RT integration more complicated > since most of the assumption are not true on PREEMPT_RT. > > Revert the optimisation since it complicates the PREEMPT_RT integration > and the improvement is hardly visible. > > [ bigeasy: Patch body around Michal's diff ] > > Link: https://lore.kernel.org/all/YgOGkXXCrD%2F1k+p4@xxxxxxxxxxxxxx > Link: https://lkml.kernel.org/r/YdX+INO9gQje6d0S@xxxxxxxxxxxxx > Signed-off-by: Michal Hocko <mhocko@xxxxxxxx> > Signed-off-by: Sebastian Andrzej Siewior <bigeasy@xxxxxxxxxxxxx> > Acked-by: Roman Gushchin <guro@xxxxxx> > Acked-by: Johannes Weiner <hannes@xxxxxxxxxxx> Reviewed-by: Shakeel Butt <shakeelb@xxxxxxxxxx>
