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From: Mark Rutland <mark.rutland@arm.com>
To: Frederic Weisbecker <frederic@kernel.org>
Cc: linux-arm-kernel@lists.infradead.org, ardb@kernel.org,
	bp@alien8.de, catalin.marinas@arm.com,
	dave.hansen@linux.intel.com, james.morse@arm.com,
	joey.gouly@arm.com, juri.lelli@redhat.com,
	linux-kernel@vger.kernel.org, luto@kernel.org, mingo@redhat.com,
	peterz@infradead.org, tglx@linutronix.de,
	valentin.schneider@arm.com, will@kernel.org
Subject: Re: [PATCH v2 5/7] sched/preempt: add PREEMPT_DYNAMIC using static keys
Date: Tue, 8 Feb 2022 12:15:37 +0000	[thread overview]
Message-ID: <YgJe6aij3iwvgRAS@FVFF77S0Q05N> (raw)
In-Reply-To: <20220207115708.GA514319@lothringen>

On Mon, Feb 07, 2022 at 12:57:08PM +0100, Frederic Weisbecker wrote:
> On Fri, Feb 04, 2022 at 03:05:55PM +0000, Mark Rutland wrote:
> > diff --git a/include/linux/entry-common.h b/include/linux/entry-common.h
> > index dfd84c59b144..141952f4fee8 100644
> > --- a/include/linux/entry-common.h
> > +++ b/include/linux/entry-common.h
> > @@ -456,13 +456,19 @@ irqentry_state_t noinstr irqentry_enter(struct pt_regs *regs);
> >   */
> >  void raw_irqentry_exit_cond_resched(void);
> >  #ifdef CONFIG_PREEMPT_DYNAMIC
> > +#if defined(CONFIG_HAVE_PREEMPT_DYNAMIC_CALL)
> >  #define irqentry_exit_cond_resched_dynamic_enabled	raw_irqentry_exit_cond_resched
> >  #define irqentry_exit_cond_resched_dynamic_disabled	NULL
> >  DECLARE_STATIC_CALL(irqentry_exit_cond_resched, raw_irqentry_exit_cond_resched);
> >  #define irqentry_exit_cond_resched()	static_call(irqentry_exit_cond_resched)()
> > -#else
> > -#define irqentry_exit_cond_resched()	raw_irqentry_exit_cond_resched()
> > +#elif defined(CONFIG_HAVE_PREEMPT_DYNAMIC_KEY)
> > +DECLARE_STATIC_KEY_TRUE(sk_dynamic_irqentry_exit_cond_resched);
> 
> If CONFIG_PREEMPT && CONFIG_PREEMPT_DYNAMIC and no "preempt=" parameter is
> passed, nothing is overriden on boot. So you need to either have cond_resched
> and might_resched initially disabled (STATIC_KEY_FALSE?) or call
> sched_dynamic_update() from preempt_dynamic_init() also when CONFIG_PREEMPT=y.

Ah; good spot. I'd missed that those were initialized to RET0.

I've changed those two to DECLARE_STATIC_KEY_FALSE(), which defaults those to
disabled, e.g.

| <dynamic_cond_resched>:
|        bti     c
|        nop     // <-------- `b <dynamic_cond_resched+0x10>` when enabled
|        mov     w0, #0x0
|        ret
|        mrs     x0, sp_el0
|        ldr     x0, [x0, #8]
|        cbnz    x0, 9d8 <dynamic_cond_resched+0x8>
|        paciasp
|        stp     x29, x30, [sp, #-16]!
|        mov     x29, sp
|        bl      900 <preempt_schedule_common>
|        mov     w0, #0x1
|        ldp     x29, x30, [sp], #16
|        autiasp
|        ret

Thanks,
Mark.

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WARNING: multiple messages have this Message-ID (diff)
From: Mark Rutland <mark.rutland@arm.com>
To: Frederic Weisbecker <frederic@kernel.org>
Cc: linux-arm-kernel@lists.infradead.org, ardb@kernel.org,
	bp@alien8.de, catalin.marinas@arm.com,
	dave.hansen@linux.intel.com, james.morse@arm.com,
	joey.gouly@arm.com, juri.lelli@redhat.com,
	linux-kernel@vger.kernel.org, luto@kernel.org, mingo@redhat.com,
	peterz@infradead.org, tglx@linutronix.de,
	valentin.schneider@arm.com, will@kernel.org
Subject: Re: [PATCH v2 5/7] sched/preempt: add PREEMPT_DYNAMIC using static keys
Date: Tue, 8 Feb 2022 12:15:37 +0000	[thread overview]
Message-ID: <YgJe6aij3iwvgRAS@FVFF77S0Q05N> (raw)
In-Reply-To: <20220207115708.GA514319@lothringen>

On Mon, Feb 07, 2022 at 12:57:08PM +0100, Frederic Weisbecker wrote:
> On Fri, Feb 04, 2022 at 03:05:55PM +0000, Mark Rutland wrote:
> > diff --git a/include/linux/entry-common.h b/include/linux/entry-common.h
> > index dfd84c59b144..141952f4fee8 100644
> > --- a/include/linux/entry-common.h
> > +++ b/include/linux/entry-common.h
> > @@ -456,13 +456,19 @@ irqentry_state_t noinstr irqentry_enter(struct pt_regs *regs);
> >   */
> >  void raw_irqentry_exit_cond_resched(void);
> >  #ifdef CONFIG_PREEMPT_DYNAMIC
> > +#if defined(CONFIG_HAVE_PREEMPT_DYNAMIC_CALL)
> >  #define irqentry_exit_cond_resched_dynamic_enabled	raw_irqentry_exit_cond_resched
> >  #define irqentry_exit_cond_resched_dynamic_disabled	NULL
> >  DECLARE_STATIC_CALL(irqentry_exit_cond_resched, raw_irqentry_exit_cond_resched);
> >  #define irqentry_exit_cond_resched()	static_call(irqentry_exit_cond_resched)()
> > -#else
> > -#define irqentry_exit_cond_resched()	raw_irqentry_exit_cond_resched()
> > +#elif defined(CONFIG_HAVE_PREEMPT_DYNAMIC_KEY)
> > +DECLARE_STATIC_KEY_TRUE(sk_dynamic_irqentry_exit_cond_resched);
> 
> If CONFIG_PREEMPT && CONFIG_PREEMPT_DYNAMIC and no "preempt=" parameter is
> passed, nothing is overriden on boot. So you need to either have cond_resched
> and might_resched initially disabled (STATIC_KEY_FALSE?) or call
> sched_dynamic_update() from preempt_dynamic_init() also when CONFIG_PREEMPT=y.

Ah; good spot. I'd missed that those were initialized to RET0.

I've changed those two to DECLARE_STATIC_KEY_FALSE(), which defaults those to
disabled, e.g.

| <dynamic_cond_resched>:
|        bti     c
|        nop     // <-------- `b <dynamic_cond_resched+0x10>` when enabled
|        mov     w0, #0x0
|        ret
|        mrs     x0, sp_el0
|        ldr     x0, [x0, #8]
|        cbnz    x0, 9d8 <dynamic_cond_resched+0x8>
|        paciasp
|        stp     x29, x30, [sp, #-16]!
|        mov     x29, sp
|        bl      900 <preempt_schedule_common>
|        mov     w0, #0x1
|        ldp     x29, x30, [sp], #16
|        autiasp
|        ret

Thanks,
Mark.

  reply	other threads:[~2022-02-08 12:17 UTC|newest]

Thread overview: 25+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2022-02-04 15:05 [PATCH v2 0/7] arm64 / sched/preempt: support PREEMPT_DYNAMIC with static keys Mark Rutland
2022-02-04 15:05 ` Mark Rutland
2022-02-04 15:05 ` [PATCH v2 1/7] sched/preempt: move PREEMPT_DYNAMIC logic later Mark Rutland
2022-02-04 15:05   ` Mark Rutland
2022-02-04 15:05 ` [PATCH v2 2/7] sched/preempt: refactor sched_dynamic_update() Mark Rutland
2022-02-04 15:05   ` Mark Rutland
2022-02-04 15:05 ` [PATCH v2 3/7] sched/preempt: simplify irqentry_exit_cond_resched() callers Mark Rutland
2022-02-04 15:05   ` Mark Rutland
2022-02-04 15:05 ` [PATCH v2 4/7] sched/preempt: decouple HAVE_PREEMPT_DYNAMIC from GENERIC_ENTRY Mark Rutland
2022-02-04 15:05   ` Mark Rutland
2022-02-04 15:05 ` [PATCH v2 5/7] sched/preempt: add PREEMPT_DYNAMIC using static keys Mark Rutland
2022-02-04 15:05   ` Mark Rutland
2022-02-07 11:57   ` Frederic Weisbecker
2022-02-07 11:57     ` Frederic Weisbecker
2022-02-08 12:15     ` Mark Rutland [this message]
2022-02-08 12:15       ` Mark Rutland
2022-02-04 15:05 ` [PATCH v2 6/7] arm64: entry: centralize premeption decision Mark Rutland
2022-02-04 15:05   ` Mark Rutland
2022-02-04 18:46   ` Catalin Marinas
2022-02-04 18:46     ` Catalin Marinas
2022-02-04 15:05 ` [PATCH v2 7/7] arm64: support PREEMPT_DYNAMIC Mark Rutland
2022-02-04 15:05   ` Mark Rutland
2022-02-04 18:48   ` Catalin Marinas
2022-02-04 18:48     ` Catalin Marinas
2022-02-04 20:41   ` kernel test robot

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