Re: [PATCH 2/6] sched/preempt: refactor sched_dynamic_update()

From: Mark Rutland
Date: Wed Feb 02 2022 - 10:14:27 EST

Hi,

I'm looking at what I need to do to rebase/repost this atop v5.17-rc2, and I
realised I need your S-o-B to take your suggestion below.

On Fri, Dec 10, 2021 at 04:13:43PM +0100, Frederic Weisbecker wrote:
> On Tue, Nov 09, 2021 at 05:24:04PM +0000, Mark Rutland wrote:
> > Currently sched_dynamic_update needs to open-code the enabled/disabled
> > function names for each preemption model it supoprts, when in practice
> > this is a boolean enabled/disabled state for each function.
> >
> > Make this clearer and avoid repetition by defining the enabled/disabled
> > states at the function definition, and using helper macros to peform the
> > static_call_update(). Where x86 currently overrides the enabled
> > function, it is made to provide both the enabled and disabled states for
> > consistency, with defaults provided by the core code otherwise.

> > -#define __preempt_schedule_notrace_func preempt_schedule_notrace_thunk
> > +#define preempt_schedule_notrace_dynamic_enabled preempt_schedule_notrace_thunk
> > +#define preempt_schedule_notrace_dynamic_disabled NULL
>
> I'm worried about un-greppable macro definitions like this.
I assume you mean that it's hard to go from:

preempt_dynamic_enable(preempt_schedule_notrace);

... to this, because the `_dynamic_enabled` or `_dynamic_disabled` part gets
token-pasted on?

The above will show up in a grep for `preempt_schedule_notrace`, but I agree
it's not necessarily ideal, especially if grepping for an exact match.

> Also this enable/disable switch look like a common pattern on static call so
> how about moving that logic to static call itself? As in below (only
> build-tested):

Sure; if others also prefer that I'm more than happy to build atop.

Can I have your Signed-off-by for that, or can you post that as its own patch?

Thanks,
Mark.

>
> diff --git a/arch/x86/include/asm/preempt.h b/arch/x86/include/asm/preempt.h
> index fe5efbcba824..64320c0a00a6 100644
> --- a/arch/x86/include/asm/preempt.h
> +++ b/arch/x86/include/asm/preempt.h
> @@ -117,7 +117,7 @@ extern asmlinkage void preempt_schedule_notrace_thunk(void);
>
> #ifdef CONFIG_PREEMPT_DYNAMIC
>
> -DECLARE_STATIC_CALL(preempt_schedule, __preempt_schedule_func);
> +DECLARE_STATIC_CALL_TOGGLE(preempt_schedule, __preempt_schedule_func);
>
> #define __preempt_schedule() \
> do { \
> @@ -125,7 +125,7 @@ do { \
> asm volatile ("call " STATIC_CALL_TRAMP_STR(preempt_schedule) : ASM_CALL_CONSTRAINT); \
> } while (0)
>
> -DECLARE_STATIC_CALL(preempt_schedule_notrace, __preempt_schedule_notrace_func);
> +DECLARE_STATIC_CALL_TOGGLE(preempt_schedule_notrace, __preempt_schedule_notrace_func);
>
> #define __preempt_schedule_notrace() \
> do { \
> diff --git a/include/linux/entry-common.h b/include/linux/entry-common.h
> index 2e2b8d6140ed..a3d99ffc32ca 100644
> --- a/include/linux/entry-common.h
> +++ b/include/linux/entry-common.h
> @@ -456,7 +456,7 @@ irqentry_state_t noinstr irqentry_enter(struct pt_regs *regs);
> */
> void irqentry_exit_cond_resched(void);
> #ifdef CONFIG_PREEMPT_DYNAMIC
> -DECLARE_STATIC_CALL(irqentry_exit_cond_resched, irqentry_exit_cond_resched);
> +DECLARE_STATIC_CALL_TOGGLE(irqentry_exit_cond_resched, irqentry_exit_cond_resched);
> #endif
>
> /**
> diff --git a/include/linux/kernel.h b/include/linux/kernel.h
> index 77755ac3e189..f4f5f4f3b496 100644
> --- a/include/linux/kernel.h
> +++ b/include/linux/kernel.h
> @@ -94,7 +94,7 @@ extern int __cond_resched(void);
>
> extern int __cond_resched(void);
>
> -DECLARE_STATIC_CALL(might_resched, __cond_resched);
> +DECLARE_STATIC_CALL_TOGGLE(might_resched, __cond_resched);
>
> static __always_inline void might_resched(void)
> {
> diff --git a/include/linux/sched.h b/include/linux/sched.h
> index 78c351e35fec..01a9e8590ea0 100644
> --- a/include/linux/sched.h
> +++ b/include/linux/sched.h
> @@ -2010,7 +2010,7 @@ extern int __cond_resched(void);
>
> #ifdef CONFIG_PREEMPT_DYNAMIC
>
> -DECLARE_STATIC_CALL(cond_resched, __cond_resched);
> +DECLARE_STATIC_CALL_TOGGLE(cond_resched, __cond_resched);
>
> static __always_inline int _cond_resched(void)
> {
> diff --git a/include/linux/static_call.h b/include/linux/static_call.h
> index 3e56a9751c06..351ac27fa9d1 100644
> --- a/include/linux/static_call.h
> +++ b/include/linux/static_call.h
> @@ -156,6 +156,19 @@ extern void arch_static_call_transform(void *site, void *tramp, void *func, bool
> STATIC_CALL_TRAMP_ADDR(name), __F); \
> })
>
> +#define static_call_toggle(name, enable) \
> +({ \
> + struct static_call_toggle *__G = &STATIC_CALL_TOGGLE(name); \
> + if (enable) \
> + static_call_update(name, __G->func_enabled); \
> + else \
> + static_call_update(name, __G->func_disabled); \
> +})
> +
> +#define static_call_enable(name) static_call_toggle(name, 1);
> +#define static_call_disable(name) static_call_toggle(name, 0);
> +
> +
> #define static_call_query(name) (READ_ONCE(STATIC_CALL_KEY(name).func))
>
> #ifdef CONFIG_HAVE_STATIC_CALL_INLINE
> @@ -333,4 +346,27 @@ static inline int static_call_text_reserved(void *start, void *end)
> #define DEFINE_STATIC_CALL_RET0(name, _func) \
> __DEFINE_STATIC_CALL(name, _func, __static_call_return0)
>
> +#define __DEFINE_STATIC_CALL_TOGGLE(name, _func_enabled, _func_disabled) \
> + struct static_call_toggle STATIC_CALL_TOGGLE(name) = { \
> + .key = &STATIC_CALL_KEY(name), \
> + .func_enabled = _func_enabled, \
> + .func_disabled = _func_disabled, \
> + }
> +
> +#define DEFINE_STATIC_CALL_ENABLED(name, _func) \
> + DEFINE_STATIC_CALL(name, _func); \
> + __DEFINE_STATIC_CALL_TOGGLE(name, _func, NULL)
> +
> +#define DEFINE_STATIC_CALL_DISABLED(name, _func) \
> + DEFINE_STATIC_CALL_NULL(name, _func); \
> + __DEFINE_STATIC_CALL_TOGGLE(name, _func, NULL)
> +
> +#define DEFINE_STATIC_CALL_ENABLED_RET0(name, _func) \
> + DEFINE_STATIC_CALL(name, _func); \
> + __DEFINE_STATIC_CALL_TOGGLE(name, _func, __static_call_return0)
> +
> +#define DEFINE_STATIC_CALL_DISABLED_RET0(name, _func) \
> + DEFINE_STATIC_CALL_RET0(name, _func); \
> + __DEFINE_STATIC_CALL_TOGGLE(name, _func, __static_call_return0)
> +
> #endif /* _LINUX_STATIC_CALL_H */
> diff --git a/include/linux/static_call_types.h b/include/linux/static_call_types.h
> index 5a00b8b2cf9f..e150f29aee2d 100644
> --- a/include/linux/static_call_types.h
> +++ b/include/linux/static_call_types.h
> @@ -18,6 +18,9 @@
> #define STATIC_CALL_TRAMP(name) __PASTE(STATIC_CALL_TRAMP_PREFIX, name)
> #define STATIC_CALL_TRAMP_STR(name) __stringify(STATIC_CALL_TRAMP(name))
>
> +#define STATIC_CALL_TOGGLE_PREFIX __SCG_
> +#define STATIC_CALL_TOGGLE(name) __PASTE(STATIC_CALL_TOGGLE_PREFIX, name)
> +
> /*
> * Flags in the low bits of static_call_site::key.
> */
> @@ -38,6 +41,10 @@ struct static_call_site {
> extern struct static_call_key STATIC_CALL_KEY(name); \
> extern typeof(func) STATIC_CALL_TRAMP(name);
>
> +#define DECLARE_STATIC_CALL_TOGGLE(name, func) \
> + DECLARE_STATIC_CALL(name, func); \
> + extern struct static_call_toggle STATIC_CALL_TOGGLE(name);
> +
> #ifdef CONFIG_HAVE_STATIC_CALL
>
> #define __raw_static_call(name) (&STATIC_CALL_TRAMP(name))
> @@ -68,6 +75,13 @@ struct static_call_key {
> };
> };
>
> +struct static_call_toggle {
> + struct static_call_key *key;
> + void *func_enabled;
> + void *func_disabled;
> +};
> +
> +
> #else /* !CONFIG_HAVE_STATIC_CALL_INLINE */
>
> #define __STATIC_CALL_ADDRESSABLE(name)
> diff --git a/kernel/entry/common.c b/kernel/entry/common.c
> index d5a61d565ad5..d48b91579475 100644
> --- a/kernel/entry/common.c
> +++ b/kernel/entry/common.c
> @@ -392,7 +392,7 @@ void irqentry_exit_cond_resched(void)
> }
> }
> #ifdef CONFIG_PREEMPT_DYNAMIC
> -DEFINE_STATIC_CALL(irqentry_exit_cond_resched, irqentry_exit_cond_resched);
> +DEFINE_STATIC_CALL_ENABLED(irqentry_exit_cond_resched, irqentry_exit_cond_resched);
> #endif
>
> noinstr void irqentry_exit(struct pt_regs *regs, irqentry_state_t state)
> diff --git a/kernel/sched/core.c b/kernel/sched/core.c
> index 27c795fbcaaf..389fcc412e6b 100644
> --- a/kernel/sched/core.c
> +++ b/kernel/sched/core.c
> @@ -6447,7 +6447,7 @@ NOKPROBE_SYMBOL(preempt_schedule);
> EXPORT_SYMBOL(preempt_schedule);
>
> #ifdef CONFIG_PREEMPT_DYNAMIC
> -DEFINE_STATIC_CALL(preempt_schedule, __preempt_schedule_func);
> +DEFINE_STATIC_CALL_ENABLED(preempt_schedule, __preempt_schedule_func);
> EXPORT_STATIC_CALL_TRAMP(preempt_schedule);
> #endif
>
> @@ -6505,7 +6505,7 @@ asmlinkage __visible void __sched notrace preempt_schedule_notrace(void)
> EXPORT_SYMBOL_GPL(preempt_schedule_notrace);
>
> #ifdef CONFIG_PREEMPT_DYNAMIC
> -DEFINE_STATIC_CALL(preempt_schedule_notrace, __preempt_schedule_notrace_func);
> +DEFINE_STATIC_CALL_ENABLED(preempt_schedule_notrace, __preempt_schedule_notrace_func);
> EXPORT_STATIC_CALL_TRAMP(preempt_schedule_notrace);
> #endif
>
> @@ -8016,10 +8016,9 @@ EXPORT_SYMBOL(__cond_resched);
> #endif
>
> #ifdef CONFIG_PREEMPT_DYNAMIC
> -DEFINE_STATIC_CALL_RET0(cond_resched, __cond_resched);
> +DEFINE_STATIC_CALL_DISABLED_RET0(cond_resched, __cond_resched);
> EXPORT_STATIC_CALL_TRAMP(cond_resched);
> -
> -DEFINE_STATIC_CALL_RET0(might_resched, __cond_resched);
> +DEFINE_STATIC_CALL_DISABLED_RET0(might_resched, __cond_resched);
> EXPORT_STATIC_CALL_TRAMP(might_resched);
> #endif
>
> @@ -8154,37 +8153,37 @@ void sched_dynamic_update(int mode)
> * Avoid {NONE,VOLUNTARY} -> FULL transitions from ever ending up in
> * the ZERO state, which is invalid.
> */
> - static_call_update(cond_resched, __cond_resched);
> - static_call_update(might_resched, __cond_resched);
> - static_call_update(preempt_schedule, __preempt_schedule_func);
> - static_call_update(preempt_schedule_notrace, __preempt_schedule_notrace_func);
> - static_call_update(irqentry_exit_cond_resched, irqentry_exit_cond_resched);
> + static_call_enable(cond_resched);
> + static_call_enable(might_resched);
> + static_call_enable(preempt_schedule);
> + static_call_enable(preempt_schedule_notrace);
> + static_call_enable(irqentry_exit_cond_resched);
>
> switch (mode) {
> case preempt_dynamic_none:
> - static_call_update(cond_resched, __cond_resched);
> - static_call_update(might_resched, (void *)&__static_call_return0);
> - static_call_update(preempt_schedule, NULL);
> - static_call_update(preempt_schedule_notrace, NULL);
> - static_call_update(irqentry_exit_cond_resched, NULL);
> + static_call_enable(cond_resched);
> + static_call_disable(might_resched);
> + static_call_disable(preempt_schedule);
> + static_call_disable(preempt_schedule_notrace);
> + static_call_disable(irqentry_exit_cond_resched);
> pr_info("Dynamic Preempt: none\n");
> break;
>
> case preempt_dynamic_voluntary:
> - static_call_update(cond_resched, __cond_resched);
> - static_call_update(might_resched, __cond_resched);
> - static_call_update(preempt_schedule, NULL);
> - static_call_update(preempt_schedule_notrace, NULL);
> - static_call_update(irqentry_exit_cond_resched, NULL);
> + static_call_enable(cond_resched);
> + static_call_enable(might_resched);
> + static_call_disable(preempt_schedule);
> + static_call_disable(preempt_schedule_notrace);
> + static_call_disable(irqentry_exit_cond_resched);
> pr_info("Dynamic Preempt: voluntary\n");
> break;
>
> case preempt_dynamic_full:
> - static_call_update(cond_resched, (void *)&__static_call_return0);
> - static_call_update(might_resched, (void *)&__static_call_return0);
> - static_call_update(preempt_schedule, __preempt_schedule_func);
> - static_call_update(preempt_schedule_notrace, __preempt_schedule_notrace_func);
> - static_call_update(irqentry_exit_cond_resched, irqentry_exit_cond_resched);
> + static_call_disable(cond_resched);
> + static_call_disable(might_resched);
> + static_call_enable(preempt_schedule);
> + static_call_enable(preempt_schedule_notrace);
> + static_call_enable(irqentry_exit_cond_resched);
> pr_info("Dynamic Preempt: full\n");
> break;
> }