On Wed, 08 Nov 2023 16:38:11 +0100 Thomas Gleixner <tglx@xxxxxxxxxxxxx> wrote: > On Wed, Nov 08 2023 at 11:13, Peter Zijlstra wrote: > > On Wed, Nov 08, 2023 at 02:04:02AM -0800, Ankur Arora wrote: > > I'm not understanding, those should stay obviously. > > > > The current preempt_dynamic stuff has 5 toggles: > > > > /* > > * SC:cond_resched > > * SC:might_resched > > * SC:preempt_schedule > > * SC:preempt_schedule_notrace > > * SC:irqentry_exit_cond_resched > > * > > * > > * NONE: > > * cond_resched <- __cond_resched > > * might_resched <- RET0 > > * preempt_schedule <- NOP > > * preempt_schedule_notrace <- NOP > > * irqentry_exit_cond_resched <- NOP > > * > > * VOLUNTARY: > > * cond_resched <- __cond_resched > > * might_resched <- __cond_resched > > * preempt_schedule <- NOP > > * preempt_schedule_notrace <- NOP > > * irqentry_exit_cond_resched <- NOP > > * > > * FULL: > > * cond_resched <- RET0 > > * might_resched <- RET0 > > * preempt_schedule <- preempt_schedule > > * preempt_schedule_notrace <- preempt_schedule_notrace > > * irqentry_exit_cond_resched <- irqentry_exit_cond_resched > > */ > > > > If you kill voluntary as we know it today, you can remove cond_resched > > and might_resched, but the remaining 3 are still needed to switch > > between NONE and FULL. > > No. The whole point of LAZY is to keep preempt_schedule(), > preempt_schedule_notrace(), irqentry_exit_cond_resched() always enabled. Right. * NONE: * cond_resched <- __cond_resched * might_resched <- RET0 * preempt_schedule <- NOP * preempt_schedule_notrace <- NOP * irqentry_exit_cond_resched <- NOP Peter, how can you say we can get rid of cond_resched() in NONE when you show that NONE still uses it? I thought the entire point of this was to get rid of all the cond_resched() and they are there for PREEMPT_NONE as well as VOLUNTARY. As you showed above, the only difference between NONE and VOLUNTARY was the might_sleep. > > Look at my PoC: https://lore.kernel.org/lkml/87jzshhexi.ffs@tglx/ And I've been saying that many times already ;-) Thanks Thomas for reiterating it. -- Steve
