Messages in this thread | | | Date | Thu, 16 Nov 2023 13:48:47 -0500 | From | Frederic Weisbecker <> | Subject | Re: [PATCH 3/4] x86: Remove __current_clr_polling() from mwait_idle() |
| |
Le Thu, Nov 16, 2023 at 04:13:16PM +0100, Peter Zijlstra a écrit : > On Wed, Nov 15, 2023 at 10:13:24AM -0500, Frederic Weisbecker wrote: > > mwait_idle() is only ever called through by cpuidle, either from > > default_idle_call() or from cpuidle_enter(). In any case > > cpuidle_idle_call() sets again TIF_NR_POLLING after calling it so there > > is no point for this atomic operation upon idle exit. > > > > Acked-by: Rafael J. Wysocki <rafael@kernel.org> > > Signed-off-by: Frederic Weisbecker <frederic@kernel.org> > > --- > > arch/x86/kernel/process.c | 1 - > > 1 file changed, 1 deletion(-) > > > > diff --git a/arch/x86/kernel/process.c b/arch/x86/kernel/process.c > > index b6f4e8399fca..fc7a38084606 100644 > > --- a/arch/x86/kernel/process.c > > +++ b/arch/x86/kernel/process.c > > @@ -930,7 +930,6 @@ static __cpuidle void mwait_idle(void) > > raw_local_irq_disable(); > > } > > } > > - __current_clr_polling(); > > } > > > > void select_idle_routine(const struct cpuinfo_x86 *c) > > > Urgh at this and the next one... That is, yes we can do this, but it > makes these function asymmetric and doesn't actually solve the > underlying problem that all of the polling stuff is inside-out. > > Idle loop sets polling, then clears polling because it assumes all > arch/driver idle loops are non-polling, then individual drivers re-set > polling, and to be symmetric (above) clear it again, for the generic > code to set it again, only to clear it again when leaving idle. > > Follow that? ;-)
That's right :-)
> > Anyway, drivers ought to tell up-front if they're polling and then we > can avoid the whole dance and everything is better. > > Something like the very crude below.
Yeah that makes perfect sense (can I use your SoB right away?)
Though I sometimes wonder why we even bother with setting TIF_NR_POLLING for some short parts in the generic idle loop even on !mwait and !cpuidle-state-polling states.
Like for example why do we bother with setting TIF_NR_POLLING for just the portion in the generic idle loop that looks up the cpuidle state and stops the tick then clear TIF_NR_POLLING before calling wfi on ARM?
Or may be it's a frequent pattern to have a remote wake up happening while entering the idle loop?
Thanks.
| |