From: Mark Rutland <mark.rutland@arm.com>
To: Ankur Arora <ankur.a.arora@oracle.com>
Cc: linux-kernel@vger.kernel.org, tglx@linutronix.de,
peterz@infradead.org, torvalds@linux-foundation.org,
paulmck@kernel.org, akpm@linux-foundation.org, luto@kernel.org,
bp@alien8.de, dave.hansen@linux.intel.com, hpa@zytor.com,
mingo@redhat.com, juri.lelli@redhat.com,
vincent.guittot@linaro.org, willy@infradead.org, mgorman@suse.de,
jpoimboe@kernel.org, jgross@suse.com, andrew.cooper3@citrix.com,
bristot@kernel.org, mathieu.desnoyers@efficios.com,
geert@linux-m68k.org, glaubitz@physik.fu-berlin.de,
anton.ivanov@cambridgegreys.com, mattst88@gmail.com,
krypton@ulrich-teichert.org, rostedt@goodmis.org,
David.Laight@aculab.com, richard@nod.at, mjguzik@gmail.com,
jon.grimm@amd.com, bharata@amd.com, raghavendra.kt@amd.com,
boris.ostrovsky@oracle.com, konrad.wilk@oracle.com,
Arnd Bergmann <arnd@arndb.de>,
"Rafael J. Wysocki" <rafael@kernel.org>
Subject: Re: [PATCH 03/30] thread_info: tif_need_resched() now takes resched_t as param
Date: Mon, 19 Feb 2024 12:30:31 +0000 [thread overview]
Message-ID: <ZdNJ5x1XmRZwa0Zp@FVFF77S0Q05N> (raw)
In-Reply-To: <87il2qmksh.fsf@oracle.com>
On Wed, Feb 14, 2024 at 08:08:30PM -0800, Ankur Arora wrote:
>
> Mark Rutland <mark.rutland@arm.com> writes:
>
> > On Mon, Feb 12, 2024 at 09:55:27PM -0800, Ankur Arora wrote:
> >> tif_need_resched() now takes a resched_t parameter to decide the
> >> immediacy of the need-resched.
> >
> > I see at the end of the series, most callers pass a constant:
> >
> > [mark@lakrids:~/src/linux]% git grep -w tif_need_resched
> > arch/s390/include/asm/preempt.h: return !--S390_lowcore.preempt_count && tif_need_resched(NR_now);
> > arch/s390/include/asm/preempt.h: tif_need_resched(NR_now));
> > include/asm-generic/preempt.h: return !--*preempt_count_ptr() && tif_need_resched(NR_now);
> > include/asm-generic/preempt.h: tif_need_resched(NR_now));
> > include/linux/preempt.h: if (tif_need_resched(NR_now)) \
> > include/linux/sched.h: return unlikely(tif_need_resched(NR_now));
> > include/linux/sched.h: unlikely(tif_need_resched(NR_lazy));
> > include/linux/thread_info.h:static __always_inline bool tif_need_resched(resched_t rs)
> > include/linux/thread_info.h: * With !PREEMPT_AUTO tif_need_resched(NR_lazy) is defined
> > kernel/entry/common.c: if (tif_need_resched(NR_now))
> > kernel/sched/debug.c: nr = tif_need_resched(NR_now) ? "need_resched" : "need_resched_lazy";
> > kernel/trace/trace.c: if (tif_need_resched(NR_now))
> > kernel/trace/trace.c: if (tif_need_resched(NR_lazy))
> >
> > I think it'd be clearer if we had tif_need_resched_now() and
> > tif_need_resched_lazy() wrappers rather than taking a parameter. I think that
> > if we did similar elsewhere (e.g. {set,test}_tsk_need_resched_{now,lazy}()),
> > it'd be a bit cleaner overall, since we can special-case the lazy behaviour
> > more easily/clearly.
>
> So, we have three need-resched interfaces:
>
> 1. need_resched(), need_resched_lazy()
> These are used all over non-core (and idle) code, and I don't
> see a case where the user would find it useful to dynamically
> choose one or the other.
> So, here two separate interfaces, need_resched()/need_resched_lazy()
> make sense.
>
> 2. tif_need_resched()
> This is mostly used from preempt.h or scheduler adjacent code to drive
> preemption and at least in current uses, the resched_t param is a
> compile time constant.
>
> I think the scheduler might find it useful in some cases to parametrize
> it (ex. maybe the scheduler knows how long which bit has been set for
> over long and wants to pass that on to resched_latency_warn().)
>
> But that's a contrived example. I think this one would be fine
> either way. Will try it out and see which (tif_need_resched(rs),
> or tif_need_resched_now()/tif_need_resched_lazy()) seems cleaner.
>
> 3. *_tsk_need_resched()
> This is is used almost entirely from the scheduler and RCU.
>
> One place where I found the ability to parametrize quite useful
> was __resched_curr(). So this I would like to keep.
>
> All of that said, and I wonder if we need these new interfaces at all.
> Most of the code only uses the NR_now interface. Only the scheduler and
> the entry code need to distinguish between lazy and eager.
> (Plus, this way lazy and eager becomes an implementation detail which
> doesn't need to be known outside the scheduler. Which is also kind of
> the point of PREEMPT_AUTO.)
>
> Say something like the patch below (and similar for tif_need_resched(),
> need_resched() etc.)
>
> What do you think?
>
> Ankur
>
> ---------
> diff --git a/include/linux/sched.h b/include/linux/sched.h
> index 58e6ea7572a0..b836b238b117 100644
> --- a/include/linux/sched.h
> +++ b/include/linux/sched.h
> @@ -1953,7 +1953,7 @@ static inline bool test_tsk_thread_flag(struct task_struct *tsk, int flag)
> * tif_resched(NR_now). Add a check in the helpers below to ensure
> * we don't touch the tif_reshed(NR_now) bit unnecessarily.
> */
> -static inline void set_tsk_need_resched(struct task_struct *tsk, resched_t rs)
> +static inline void __set_tsk_need_resched(struct task_struct *tsk, resched_t rs)
> {
> if (IS_ENABLED(CONFIG_PREEMPT_AUTO) || rs == NR_now)
> set_tsk_thread_flag(tsk, tif_resched(rs));
> @@ -1964,6 +1964,11 @@ static inline void set_tsk_need_resched(struct task_struct *tsk, resched_t rs)
> BUG();
> }
>
> +static inline void set_tsk_need_resched(struct task_struct *tsk, resched_t rs)
> +{
> + __set_tsk_need_resched(tsk, NR_now);
> +}
I assume for this (and test_tsk_need_resched() below), you mean to drop the
resched_t argument, i.e. this should be:
static inline void set_tsk_need_resched(struct task_struct *tsk)
{
__set_tsk_need_resched(tsk, NR_now);
}
Assuming so, this looks good to me!
Mark.
> +
> static inline void clear_tsk_need_resched(struct task_struct *tsk)
> {
> clear_tsk_thread_flag(tsk, tif_resched(NR_now));
> @@ -1972,7 +1977,7 @@ static inline void clear_tsk_need_resched(struct task_struct *tsk)
> clear_tsk_thread_flag(tsk, tif_resched(NR_lazy));
> }
>
> -static inline bool test_tsk_need_resched(struct task_struct *tsk, resched_t rs)
> +static inline bool __test_tsk_need_resched(struct task_struct *tsk, resched_t rs)
> {
> if (IS_ENABLED(CONFIG_PREEMPT_AUTO) || rs == NR_now)
> return unlikely(test_tsk_thread_flag(tsk, tif_resched(rs)));
> @@ -1980,6 +1985,11 @@ static inline bool test_tsk_need_resched(struct task_struct *tsk, resched_t rs)
> return false;
> }
>
> +static inline bool test_tsk_need_resched(struct task_struct *tsk, resched_t rs)
> +{
> + return __test_tsk_need_resched(tsk, NR_now);
> +}
> +
> /*
> * cond_resched() and cond_resched_lock(): latency reduction via
> * explicit rescheduling in places that are safe. The return
next prev parent reply other threads:[~2024-02-19 12:30 UTC|newest]
Thread overview: 155+ messages / expand[flat|nested] mbox.gz Atom feed top
2024-02-13 5:55 [PATCH 00/30] PREEMPT_AUTO: support lazy rescheduling Ankur Arora
2024-02-13 5:55 ` [PATCH 01/30] preempt: introduce CONFIG_PREEMPT_AUTO Ankur Arora
2024-02-13 5:55 ` [PATCH 02/30] thread_info: selector for TIF_NEED_RESCHED[_LAZY] Ankur Arora
2024-02-19 15:16 ` Thomas Gleixner
2024-02-20 22:50 ` Ankur Arora
2024-02-21 17:05 ` Thomas Gleixner
2024-02-21 18:26 ` Steven Rostedt
2024-02-21 20:03 ` Thomas Gleixner
2024-02-13 5:55 ` [PATCH 03/30] thread_info: tif_need_resched() now takes resched_t as param Ankur Arora
2024-02-14 3:17 ` kernel test robot
2024-02-14 14:08 ` Mark Rutland
2024-02-15 4:08 ` Ankur Arora
2024-02-19 12:30 ` Mark Rutland [this message]
2024-02-20 22:09 ` Ankur Arora
2024-02-19 15:21 ` Thomas Gleixner
2024-02-20 22:21 ` Ankur Arora
2024-02-21 17:07 ` Thomas Gleixner
2024-02-21 21:22 ` Ankur Arora
2024-02-13 5:55 ` [PATCH 04/30] sched: make test_*_tsk_thread_flag() return bool Ankur Arora
2024-02-14 14:12 ` Mark Rutland
2024-02-15 2:04 ` Ankur Arora
2024-02-13 5:55 ` [PATCH 05/30] sched: *_tsk_need_resched() now takes resched_t as param Ankur Arora
2024-02-19 15:26 ` Thomas Gleixner
2024-02-20 22:37 ` Ankur Arora
2024-02-21 17:10 ` Thomas Gleixner
2024-02-13 5:55 ` [PATCH 06/30] entry: handle lazy rescheduling at user-exit Ankur Arora
2024-02-19 15:29 ` Thomas Gleixner
2024-02-20 22:38 ` Ankur Arora
2024-02-13 5:55 ` [PATCH 07/30] entry/kvm: handle lazy rescheduling at guest-entry Ankur Arora
2024-02-13 5:55 ` [PATCH 08/30] entry: irqentry_exit only preempts for TIF_NEED_RESCHED Ankur Arora
2024-02-13 5:55 ` [PATCH 09/30] sched: __schedule_loop() doesn't need to check for need_resched_lazy() Ankur Arora
2024-02-13 5:55 ` [PATCH 10/30] sched: separate PREEMPT_DYNAMIC config logic Ankur Arora
2024-02-13 5:55 ` [PATCH 11/30] sched: runtime preemption config under PREEMPT_AUTO Ankur Arora
2024-02-13 5:55 ` [PATCH 12/30] rcu: limit PREEMPT_RCU to full preemption " Ankur Arora
2024-02-13 5:55 ` [PATCH 13/30] rcu: fix header guard for rcu_all_qs() Ankur Arora
2024-02-13 5:55 ` [PATCH 14/30] preempt,rcu: warn on PREEMPT_RCU=n, preempt=full Ankur Arora
2024-02-13 5:55 ` [PATCH 15/30] rcu: handle quiescent states for PREEMPT_RCU=n, PREEMPT_COUNT=y Ankur Arora
2024-03-10 10:03 ` Joel Fernandes
2024-03-10 18:56 ` Paul E. McKenney
2024-03-11 0:48 ` Joel Fernandes
2024-03-11 3:56 ` Paul E. McKenney
2024-03-11 15:01 ` Joel Fernandes
2024-03-11 20:51 ` Ankur Arora
2024-03-11 22:12 ` Thomas Gleixner
2024-03-11 5:18 ` Ankur Arora
2024-03-11 15:25 ` Joel Fernandes
2024-03-11 19:12 ` Thomas Gleixner
2024-03-11 19:53 ` Paul E. McKenney
2024-03-11 20:29 ` Thomas Gleixner
2024-03-12 0:01 ` Paul E. McKenney
2024-03-12 0:08 ` Joel Fernandes
2024-03-12 3:16 ` Ankur Arora
2024-03-12 3:24 ` Joel Fernandes
2024-03-12 5:23 ` Ankur Arora
2024-02-13 5:55 ` [PATCH 16/30] rcu: force context-switch " Ankur Arora
2024-02-13 5:55 ` [PATCH 17/30] x86/thread_info: define TIF_NEED_RESCHED_LAZY Ankur Arora
2024-02-14 13:25 ` Mark Rutland
2024-02-14 20:31 ` Ankur Arora
2024-02-19 12:32 ` Mark Rutland
2024-02-13 5:55 ` [PATCH 18/30] sched: prepare for lazy rescheduling in resched_curr() Ankur Arora
2024-02-13 5:55 ` [PATCH 19/30] sched: default preemption policy for PREEMPT_AUTO Ankur Arora
2024-02-13 5:55 ` [PATCH 20/30] sched: handle idle preemption " Ankur Arora
2024-02-13 5:55 ` [PATCH 21/30] sched: schedule eagerly in resched_cpu() Ankur Arora
2024-02-13 5:55 ` [PATCH 22/30] sched/fair: refactor update_curr(), entity_tick() Ankur Arora
2024-02-13 5:55 ` [PATCH 23/30] sched/fair: handle tick expiry under lazy preemption Ankur Arora
2024-02-21 21:38 ` Steven Rostedt
2024-02-28 13:47 ` Juri Lelli
2024-02-29 6:43 ` Ankur Arora
2024-02-29 9:33 ` Juri Lelli
2024-02-29 23:54 ` Ankur Arora
2024-03-01 0:28 ` Paul E. McKenney
2024-02-13 5:55 ` [PATCH 24/30] sched: support preempt=none under PREEMPT_AUTO Ankur Arora
2024-02-13 5:55 ` [PATCH 25/30] sched: support preempt=full " Ankur Arora
2024-02-13 5:55 ` [PATCH 26/30] sched: handle preempt=voluntary " Ankur Arora
2024-03-03 1:08 ` Joel Fernandes
2024-03-05 8:11 ` Ankur Arora
2024-03-06 20:42 ` Joel Fernandes
2024-03-07 19:01 ` Paul E. McKenney
2024-03-08 0:15 ` Joel Fernandes
2024-03-08 0:42 ` Paul E. McKenney
2024-03-08 4:22 ` Ankur Arora
2024-03-08 21:33 ` Paul E. McKenney
2024-03-11 4:50 ` Ankur Arora
2024-03-11 19:26 ` Paul E. McKenney
2024-03-11 20:09 ` Ankur Arora
2024-03-11 20:23 ` Linus Torvalds
2024-03-11 21:03 ` Ankur Arora
2024-03-12 0:03 ` Paul E. McKenney
2024-03-12 12:14 ` Thomas Gleixner
2024-03-12 19:40 ` Paul E. McKenney
2024-03-08 3:49 ` Ankur Arora
2024-03-08 5:29 ` Joel Fernandes
2024-03-08 6:54 ` Juri Lelli
2024-03-11 5:34 ` Ankur Arora
2024-02-13 5:55 ` [PATCH 27/30] sched: latency warn for TIF_NEED_RESCHED_LAZY Ankur Arora
2024-02-13 5:55 ` [PATCH 28/30] tracing: support lazy resched Ankur Arora
2024-02-13 5:55 ` [PATCH 29/30] Documentation: tracing: add TIF_NEED_RESCHED_LAZY Ankur Arora
2024-02-21 21:43 ` Steven Rostedt
2024-02-21 23:22 ` Ankur Arora
2024-02-21 23:53 ` Steven Rostedt
2024-03-01 23:33 ` Joel Fernandes
2024-03-02 3:09 ` Ankur Arora
2024-03-03 19:32 ` Joel Fernandes
2024-02-13 5:55 ` [PATCH 30/30] osnoise: handle quiescent states for PREEMPT_RCU=n, PREEMPTION=y Ankur Arora
2024-02-13 9:47 ` [PATCH 00/30] PREEMPT_AUTO: support lazy rescheduling Geert Uytterhoeven
2024-02-13 21:46 ` Ankur Arora
2024-02-14 23:57 ` Paul E. McKenney
2024-02-15 2:03 ` Ankur Arora
2024-02-15 3:45 ` Paul E. McKenney
2024-02-15 19:28 ` Paul E. McKenney
2024-02-15 20:04 ` Thomas Gleixner
2024-02-15 20:54 ` Paul E. McKenney
2024-02-15 20:53 ` Ankur Arora
2024-02-15 20:55 ` Paul E. McKenney
2024-02-15 21:24 ` Ankur Arora
2024-02-15 22:54 ` Paul E. McKenney
2024-02-15 22:56 ` Paul E. McKenney
2024-02-16 0:45 ` Ankur Arora
2024-02-16 2:59 ` Paul E. McKenney
2024-02-17 0:55 ` Paul E. McKenney
2024-02-17 3:59 ` Ankur Arora
2024-02-18 18:17 ` Paul E. McKenney
2024-02-19 16:48 ` Paul E. McKenney
2024-02-21 18:19 ` Steven Rostedt
2024-02-21 19:41 ` Paul E. McKenney
2024-02-21 20:11 ` Steven Rostedt
2024-02-21 20:22 ` Paul E. McKenney
2024-02-22 15:50 ` Mark Rutland
2024-02-22 19:11 ` Paul E. McKenney
2024-02-23 11:05 ` Mark Rutland
2024-02-23 15:31 ` Paul E. McKenney
2024-03-02 1:16 ` Paul E. McKenney
2024-03-19 11:45 ` Tasks RCU, ftrace, and trampolines (was: Re: [PATCH 00/30] PREEMPT_AUTO: support lazy rescheduling) Mark Rutland
2024-03-19 23:33 ` Paul E. McKenney
2024-02-21 6:48 ` [PATCH 00/30] PREEMPT_AUTO: support lazy rescheduling Ankur Arora
2024-02-21 17:44 ` Paul E. McKenney
2024-02-16 0:45 ` Ankur Arora
2024-02-21 12:23 ` Raghavendra K T
2024-02-21 17:15 ` Thomas Gleixner
2024-02-21 17:27 ` Raghavendra K T
2024-02-21 21:16 ` Ankur Arora
2024-02-22 4:05 ` Raghavendra K T
2024-02-22 21:23 ` Thomas Gleixner
2024-02-23 3:14 ` Ankur Arora
2024-02-23 6:28 ` Raghavendra K T
2024-02-24 3:15 ` Raghavendra K T
2024-02-27 17:45 ` Ankur Arora
2024-02-22 13:04 ` Raghavendra K T
2024-04-23 15:21 ` Shrikanth Hegde
2024-04-23 16:13 ` Linus Torvalds
2024-04-26 7:46 ` Shrikanth Hegde
2024-04-26 19:00 ` Ankur Arora
2024-05-07 11:16 ` Shrikanth Hegde
2024-05-08 5:18 ` Ankur Arora
2024-05-15 14:31 ` Shrikanth Hegde
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