Allow threads marked TIF_ALLOW_RESCHED to be rescheduled in irqexit.
This is only necessary under !preempt_model_preemptible() for which
we reuse the same logic as irqentry_exit_code_resched().
Signed-off-by: Ankur Arora <[email protected]>
---
kernel/entry/common.c | 8 ++++++++
kernel/sched/core.c | 36 +++++++++++++++++++++---------------
2 files changed, 29 insertions(+), 15 deletions(-)
diff --git a/kernel/entry/common.c b/kernel/entry/common.c
index be61332c66b5..f1005595ebe7 100644
--- a/kernel/entry/common.c
+++ b/kernel/entry/common.c
@@ -390,6 +390,9 @@ void raw_irqentry_exit_cond_resched(void)
preempt_schedule_irq();
}
}
+
+void irqentry_exit_allow_resched(void) __alias(raw_irqentry_exit_cond_resched);
+
#ifdef CONFIG_PREEMPT_DYNAMIC
#if defined(CONFIG_HAVE_PREEMPT_DYNAMIC_CALL)
DEFINE_STATIC_CALL(irqentry_exit_cond_resched, raw_irqentry_exit_cond_resched);
@@ -431,6 +434,11 @@ noinstr void irqentry_exit(struct pt_regs *regs, irqentry_state_t state)
instrumentation_begin();
if (IS_ENABLED(CONFIG_PREEMPTION))
irqentry_exit_cond_resched();
+ /*
+ * We care about this clause only in the dynamic !preemptible case.
+ */
+ if (unlikely(!preempt_model_preemptible() && resched_allowed()))
+ irqentry_exit_allow_resched();
/* Covers both tracing and lockdep */
trace_hardirqs_on();
diff --git a/kernel/sched/core.c b/kernel/sched/core.c
index 0d18c3969f90..11845a91b691 100644
--- a/kernel/sched/core.c
+++ b/kernel/sched/core.c
@@ -6500,6 +6500,8 @@ pick_next_task(struct rq *rq, struct task_struct *prev, struct rq_flags *rf)
* - explicit schedule() call
* - return from syscall or exception to user-space
* - return from interrupt-handler to user-space
+ * - return from interrupt-handler with the task having set
+ * TIF_RESCHED_ALLOW
*
* WARNING: must be called with preemption disabled!
*/
@@ -8597,28 +8599,32 @@ EXPORT_SYMBOL(__cond_resched_rwlock_write);
* SC:preempt_schedule
* SC:preempt_schedule_notrace
* SC:irqentry_exit_cond_resched
+ * SC:irqentry_exit_allow_resched
*
*
* NONE:
- * cond_resched <- __cond_resched
- * might_resched <- RET0
- * preempt_schedule <- NOP
- * preempt_schedule_notrace <- NOP
- * irqentry_exit_cond_resched <- NOP
+ * cond_resched <- __cond_resched
+ * might_resched <- RET0
+ * preempt_schedule <- NOP
+ * preempt_schedule_notrace <- NOP
+ * irqentry_exit_cond_resched <- NOP
+ * irqentry_exit_allow_resched <- irqentry_exit_allow_resched
*
* VOLUNTARY:
- * cond_resched <- __cond_resched
- * might_resched <- __cond_resched
- * preempt_schedule <- NOP
- * preempt_schedule_notrace <- NOP
- * irqentry_exit_cond_resched <- NOP
+ * cond_resched <- __cond_resched
+ * might_resched <- __cond_resched
+ * preempt_schedule <- NOP
+ * preempt_schedule_notrace <- NOP
+ * irqentry_exit_cond_resched <- NOP
+ * irqentry_exit_allow_resched <- irqentry_exit_allow_resched
*
* 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
+ * cond_resched <- RET0
+ * might_resched <- RET0
+ * preempt_schedule <- preempt_schedule
+ * preempt_schedule_notrace <- preempt_schedule_notrace
+ * irqentry_exit_cond_resched <- irqentry_exit_cond_resched
+ * irqentry_exit_allow_resched <- NOP
*/
enum {
--
2.31.1
On Sun, Apr 02 2023 at 22:22, Ankur Arora wrote:
> Allow threads marked TIF_ALLOW_RESCHED to be rescheduled in irqexit.
>
> This is only necessary under !preempt_model_preemptible() for which
> we reuse the same logic as irqentry_exit_code_resched().
This tells what this patch is doing but completely fails to explain why
this is necessary and useful.
Thanks,
tglx
Thomas Gleixner <[email protected]> writes:
> On Sun, Apr 02 2023 at 22:22, Ankur Arora wrote:
>> Allow threads marked TIF_ALLOW_RESCHED to be rescheduled in irqexit.
>>
>> This is only necessary under !preempt_model_preemptible() for which
>> we reuse the same logic as irqentry_exit_code_resched().
>
> This tells what this patch is doing but completely fails to explain why
> this is necessary and useful.
Thanks. Yeah, it does seem to miss that completely.
Needs some massaging, but does something like this clarify it's purpose?
On kernels with PREEMPTION_NONE/_VOLUNTARY, rescheduling of kernel
tasks happens when they allow it -- for instance by synchronously
calling cond_resched() in a long running task.
There are cases where it is not convenient to periodically call
cond_resched() -- for instance when executing a potentially
long running instruction (such as REP STOSB on x86).
To handle kernel code sections which can be safely preempted, but
cannot explicitly call cond_resched(), allow them to mark themselves
TIF_ALLOW_RESCHED.
Contexts marked such (via allow_resched()) can be rescheduled in the
irqexit path. This is, of course only needed with
!preempt_model_preemptible() and the rescheduling logic is functionally
same as irqentry_exit_code_resched().
--
ankur
On Sun, Apr 02, 2023 at 10:22:32PM -0700, Ankur Arora wrote:
> Allow threads marked TIF_ALLOW_RESCHED to be rescheduled in irqexit.
>
> This is only necessary under !preempt_model_preemptible() for which
> we reuse the same logic as irqentry_exit_code_resched().
>
> Signed-off-by: Ankur Arora <[email protected]>
> ---
> kernel/entry/common.c | 8 ++++++++
> kernel/sched/core.c | 36 +++++++++++++++++++++---------------
> 2 files changed, 29 insertions(+), 15 deletions(-)
>
> diff --git a/kernel/entry/common.c b/kernel/entry/common.c
> index be61332c66b5..f1005595ebe7 100644
> --- a/kernel/entry/common.c
> +++ b/kernel/entry/common.c
> @@ -390,6 +390,9 @@ void raw_irqentry_exit_cond_resched(void)
> preempt_schedule_irq();
> }
> }
> +
> +void irqentry_exit_allow_resched(void) __alias(raw_irqentry_exit_cond_resched);
Because typing raw_irqentry_exit_cond_resched() was too much effort?
> +
> #ifdef CONFIG_PREEMPT_DYNAMIC
> #if defined(CONFIG_HAVE_PREEMPT_DYNAMIC_CALL)
> DEFINE_STATIC_CALL(irqentry_exit_cond_resched, raw_irqentry_exit_cond_resched);
> @@ -431,6 +434,11 @@ noinstr void irqentry_exit(struct pt_regs *regs, irqentry_state_t state)
> instrumentation_begin();
> if (IS_ENABLED(CONFIG_PREEMPTION))
> irqentry_exit_cond_resched();
> + /*
> + * We care about this clause only in the dynamic !preemptible case.
> + */
> + if (unlikely(!preempt_model_preemptible() && resched_allowed()))
> + irqentry_exit_allow_resched();
This is wrong, if we have dynamic preemption then we have
CONFIG_PREEMPTION and we'll have that irqentry_exit_cond_resched() call.
Basically what you've written above is something like:
static_call(foo); // raw_foo() when A, NOP if !A
if (!A)
raw_foo();
And yeah, you've got the extra resched_allowed() thing in there, but
that doesn't make it any better -- this is all quite horrible.
What you really care about is the CONFIG_PREEMPTION=n case, but that you
don't actually handle.
> /* Covers both tracing and lockdep */
> trace_hardirqs_on();
> diff --git a/kernel/sched/core.c b/kernel/sched/core.c
> index 0d18c3969f90..11845a91b691 100644
> --- a/kernel/sched/core.c
> +++ b/kernel/sched/core.c
> @@ -8597,28 +8599,32 @@ EXPORT_SYMBOL(__cond_resched_rwlock_write);
> * SC:preempt_schedule
> * SC:preempt_schedule_notrace
> * SC:irqentry_exit_cond_resched
> + * SC:irqentry_exit_allow_resched
> *
> *
> * NONE:
> - * cond_resched <- __cond_resched
> - * might_resched <- RET0
> - * preempt_schedule <- NOP
> - * preempt_schedule_notrace <- NOP
> - * irqentry_exit_cond_resched <- NOP
> + * cond_resched <- __cond_resched
> + * might_resched <- RET0
> + * preempt_schedule <- NOP
> + * preempt_schedule_notrace <- NOP
> + * irqentry_exit_cond_resched <- NOP
> + * irqentry_exit_allow_resched <- irqentry_exit_allow_resched
> *
> * VOLUNTARY:
> - * cond_resched <- __cond_resched
> - * might_resched <- __cond_resched
> - * preempt_schedule <- NOP
> - * preempt_schedule_notrace <- NOP
> - * irqentry_exit_cond_resched <- NOP
> + * cond_resched <- __cond_resched
> + * might_resched <- __cond_resched
> + * preempt_schedule <- NOP
> + * preempt_schedule_notrace <- NOP
> + * irqentry_exit_cond_resched <- NOP
> + * irqentry_exit_allow_resched <- irqentry_exit_allow_resched
> *
> * 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
> + * cond_resched <- RET0
> + * might_resched <- RET0
> + * preempt_schedule <- preempt_schedule
> + * preempt_schedule_notrace <- preempt_schedule_notrace
> + * irqentry_exit_cond_resched <- irqentry_exit_cond_resched
> + * irqentry_exit_allow_resched <- NOP
> */
This ^ is all complete nonsense.. irqentry_exit_allow_resched() is not
a static call. It's an alias of raw_irqentry_exit_cond_resched which
circumvents the static call entirely.
Peter Zijlstra <[email protected]> writes:
> On Sun, Apr 02, 2023 at 10:22:32PM -0700, Ankur Arora wrote:
>> Allow threads marked TIF_ALLOW_RESCHED to be rescheduled in irqexit.
>>
>> This is only necessary under !preempt_model_preemptible() for which
>> we reuse the same logic as irqentry_exit_code_resched().
>>
>> Signed-off-by: Ankur Arora <[email protected]>
>> ---
>> kernel/entry/common.c | 8 ++++++++
>> kernel/sched/core.c | 36 +++++++++++++++++++++---------------
>> 2 files changed, 29 insertions(+), 15 deletions(-)
>>
>> diff --git a/kernel/entry/common.c b/kernel/entry/common.c
>> index be61332c66b5..f1005595ebe7 100644
>> --- a/kernel/entry/common.c
>> +++ b/kernel/entry/common.c
>> @@ -390,6 +390,9 @@ void raw_irqentry_exit_cond_resched(void)
>> preempt_schedule_irq();
>> }
>> }
>> +
>> +void irqentry_exit_allow_resched(void) __alias(raw_irqentry_exit_cond_resched);
>
> Because typing raw_irqentry_exit_cond_resched() was too much effort?
Probably unnecessary but wanted to underscore that irqentry_exit_allow_resched()
handled a separate user path.
>> +
>> #ifdef CONFIG_PREEMPT_DYNAMIC
>> #if defined(CONFIG_HAVE_PREEMPT_DYNAMIC_CALL)
>> DEFINE_STATIC_CALL(irqentry_exit_cond_resched, raw_irqentry_exit_cond_resched);
>> @@ -431,6 +434,11 @@ noinstr void irqentry_exit(struct pt_regs *regs, irqentry_state_t state)
>> instrumentation_begin();
>> if (IS_ENABLED(CONFIG_PREEMPTION))
>> irqentry_exit_cond_resched();
>> + /*
>> + * We care about this clause only in the dynamic !preemptible case.
>> + */
>> + if (unlikely(!preempt_model_preemptible() && resched_allowed()))
>> + irqentry_exit_allow_resched();
>
> This is wrong, if we have dynamic preemption then we have
> CONFIG_PREEMPTION and we'll have that irqentry_exit_cond_resched() call.
>
> Basically what you've written above is something like:
>
> static_call(foo); // raw_foo() when A, NOP if !A
Right, so:
CONFIG_PREEMPTION: raw_foo()
CONFIG_PREEMPTION && (preempt_dynamic_mode == preempt_dynamic_full): raw_foo()
This is NOP if CONFIG_PREEMPTION && preempt_dynamic_mode != preempt_dynamic_full.
> if (!A)
> raw_foo();
So I would call raw_foo() for the CONFIG_PREEMPTION=n case.
> What you really care about is the CONFIG_PREEMPTION=n case, but that you
> don't actually handle.
I don't see that. The CONFIG_PREEMPTION=n (or its dynamic version)
is being handled here.
Ignoring the RT case, preempt_model_preemptible() is either:
IS_ENABLED(CONFIG_PREEMPT)
or:
preempt_dynamic_mode == preempt_dynamic_full
So, I'm handling both the static and the dynamic case here.
if (!IS_ENABLED(CONFIG_PREEMPTION))
raw_foo()
or
if (preempt_dynamic_mode != preempt_dynamic_full)
raw_foo()
> And yeah, you've got the extra resched_allowed() thing in there, but
> that doesn't make it any better -- this is all quite horrible.
I don't disagree. There's a quite a lot of static/dynamic config options
here and adding this clause didn't improve things.
I think just going with a static call here for the allow-resched case
might have been cleaner. Alternately I'll see if it can be cleanly
folded in with the irqentry_exit_cond_resched() logic.
>> /* Covers both tracing and lockdep */
>> trace_hardirqs_on();
>> diff --git a/kernel/sched/core.c b/kernel/sched/core.c
>> index 0d18c3969f90..11845a91b691 100644
>> --- a/kernel/sched/core.c
>> +++ b/kernel/sched/core.c
>
>> @@ -8597,28 +8599,32 @@ EXPORT_SYMBOL(__cond_resched_rwlock_write);
>> * SC:preempt_schedule
>> * SC:preempt_schedule_notrace
>> * SC:irqentry_exit_cond_resched
>> + * SC:irqentry_exit_allow_resched
>> *
>> *
>> * NONE:
>> - * cond_resched <- __cond_resched
>> - * might_resched <- RET0
>> - * preempt_schedule <- NOP
>> - * preempt_schedule_notrace <- NOP
>> - * irqentry_exit_cond_resched <- NOP
>> + * cond_resched <- __cond_resched
>> + * might_resched <- RET0
>> + * preempt_schedule <- NOP
>> + * preempt_schedule_notrace <- NOP
>> + * irqentry_exit_cond_resched <- NOP
>> + * irqentry_exit_allow_resched <- irqentry_exit_allow_resched
>> *
>> * VOLUNTARY:
>> - * cond_resched <- __cond_resched
>> - * might_resched <- __cond_resched
>> - * preempt_schedule <- NOP
>> - * preempt_schedule_notrace <- NOP
>> - * irqentry_exit_cond_resched <- NOP
>> + * cond_resched <- __cond_resched
>> + * might_resched <- __cond_resched
>> + * preempt_schedule <- NOP
>> + * preempt_schedule_notrace <- NOP
>> + * irqentry_exit_cond_resched <- NOP
>> + * irqentry_exit_allow_resched <- irqentry_exit_allow_resched
>> *
>> * 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
>> + * cond_resched <- RET0
>> + * might_resched <- RET0
>> + * preempt_schedule <- preempt_schedule
>> + * preempt_schedule_notrace <- preempt_schedule_notrace
>> + * irqentry_exit_cond_resched <- irqentry_exit_cond_resched
>> + * irqentry_exit_allow_resched <- NOP
>> */
>
> This ^ is all complete nonsense.. irqentry_exit_allow_resched() is not
> a static call. It's an alias of raw_irqentry_exit_cond_resched which
> circumvents the static call entirely.
Yeah you are right. I added the SC:irqentry_exit_allow_resched
prematurely. Will fix.
Thanks for the detailed comments.
--
ankur
On Thu, Apr 06, 2023 at 09:56:07AM -0700, Ankur Arora wrote:
>
> Right, so:
>
> CONFIG_PREEMPTION: raw_foo()
> CONFIG_PREEMPTION && (preempt_dynamic_mode == preempt_dynamic_full): raw_foo()
>
> This is NOP if CONFIG_PREEMPTION && preempt_dynamic_mode != preempt_dynamic_full.
>
> > if (!A)
> > raw_foo();
>
> So I would call raw_foo() for the CONFIG_PREEMPTION=n case.
>
> > What you really care about is the CONFIG_PREEMPTION=n case, but that you
> > don't actually handle.
>
> I don't see that. The CONFIG_PREEMPTION=n (or its dynamic version)
> is being handled here.
Bah, I overlooked we have multiple definitions of the
preempt_model_foo() things. For some reason I thought all that was only
for DYNAMIC_PREEMPT.
> > And yeah, you've got the extra resched_allowed() thing in there, but
> > that doesn't make it any better -- this is all quite horrible.
>
> I don't disagree. There's a quite a lot of static/dynamic config options
> here and adding this clause didn't improve things.
>
> I think just going with a static call here for the allow-resched case
> might have been cleaner. Alternately I'll see if it can be cleanly
> folded in with the irqentry_exit_cond_resched() logic.
Something like the below perhaps?
---
include/linux/entry-common.h | 6 ++++++
kernel/entry/common.c | 23 +++++++++++++++++++++--
2 files changed, 27 insertions(+), 2 deletions(-)
diff --git a/include/linux/entry-common.h b/include/linux/entry-common.h
index d95ab85f96ba..0c365dc1f1c2 100644
--- a/include/linux/entry-common.h
+++ b/include/linux/entry-common.h
@@ -415,10 +415,16 @@ irqentry_state_t noinstr irqentry_enter(struct pt_regs *regs);
* Conditional reschedule with additional sanity checks.
*/
void raw_irqentry_exit_cond_resched(void);
+void irqentry_exit_cond_resched_tif(void);
+
#ifdef CONFIG_PREEMPT_DYNAMIC
#if defined(CONFIG_HAVE_PREEMPT_DYNAMIC_CALL)
#define irqentry_exit_cond_resched_dynamic_enabled raw_irqentry_exit_cond_resched
+#ifdef TIF_RESCHED_ALLOW
+#define irqentry_exit_cond_resched_dynamic_disabled irqentry_exit_cond_resched_tif
+#else
#define irqentry_exit_cond_resched_dynamic_disabled NULL
+#endif
DECLARE_STATIC_CALL(irqentry_exit_cond_resched, raw_irqentry_exit_cond_resched);
#define irqentry_exit_cond_resched() static_call(irqentry_exit_cond_resched)()
#elif defined(CONFIG_HAVE_PREEMPT_DYNAMIC_KEY)
diff --git a/kernel/entry/common.c b/kernel/entry/common.c
index be61332c66b5..211d118aa672 100644
--- a/kernel/entry/common.c
+++ b/kernel/entry/common.c
@@ -390,6 +390,21 @@ void raw_irqentry_exit_cond_resched(void)
preempt_schedule_irq();
}
}
+
+void irqentry_exit_cond_resched_tif(void)
+{
+#ifdef TIF_RESCHED_ALLOW
+ if (resched_allowed()) {
+ /* Sanity check RCU and thread stack */
+ rcu_irq_exit_check_preempt();
+ if (IS_ENABLED(CONFIG_DEBUG_ENTRY))
+ WARN_ON_ONCE(!on_thread_stack());
+ if (need_resched())
+ preempt_schedule_irq();
+ }
+#endif
+}
+
#ifdef CONFIG_PREEMPT_DYNAMIC
#if defined(CONFIG_HAVE_PREEMPT_DYNAMIC_CALL)
DEFINE_STATIC_CALL(irqentry_exit_cond_resched, raw_irqentry_exit_cond_resched);
@@ -397,8 +412,10 @@ DEFINE_STATIC_CALL(irqentry_exit_cond_resched, raw_irqentry_exit_cond_resched);
DEFINE_STATIC_KEY_TRUE(sk_dynamic_irqentry_exit_cond_resched);
void dynamic_irqentry_exit_cond_resched(void)
{
- if (!static_branch_unlikely(&sk_dynamic_irqentry_exit_cond_resched))
- return;
+ if (!static_branch_unlikely(&sk_dynamic_irqentry_exit_cond_resched)) {
+ irqentry_exit_cond_resched_tif();
+ return
+ }
raw_irqentry_exit_cond_resched();
}
#endif
@@ -431,6 +448,8 @@ noinstr void irqentry_exit(struct pt_regs *regs, irqentry_state_t state)
instrumentation_begin();
if (IS_ENABLED(CONFIG_PREEMPTION))
irqentry_exit_cond_resched();
+ else
+ irqentry_exit_cond_resched_tif();
/* Covers both tracing and lockdep */
trace_hardirqs_on();
On Thu, Apr 06, 2023 at 10:13:59PM +0200, Peter Zijlstra wrote:
> +void irqentry_exit_cond_resched_tif(void)
> +{
> +#ifdef TIF_RESCHED_ALLOW
> + if (resched_allowed()) {
> + /* Sanity check RCU and thread stack */
> + rcu_irq_exit_check_preempt();
> + if (IS_ENABLED(CONFIG_DEBUG_ENTRY))
> + WARN_ON_ONCE(!on_thread_stack());
> + if (need_resched())
> + preempt_schedule_irq();
arguably this can simply call raw_irqentry_exit_cond_resched_tif()..
probably better than duplicating all that again.
> + }
> +#endif
> +}
Peter Zijlstra <[email protected]> writes:
> On Thu, Apr 06, 2023 at 09:56:07AM -0700, Ankur Arora wrote:
>
>>
>> Right, so:
>>
>> CONFIG_PREEMPTION: raw_foo()
>> CONFIG_PREEMPTION && (preempt_dynamic_mode == preempt_dynamic_full): raw_foo()
>>
>> This is NOP if CONFIG_PREEMPTION && preempt_dynamic_mode != preempt_dynamic_full.
>>
>> > if (!A)
>> > raw_foo();
>>
>> So I would call raw_foo() for the CONFIG_PREEMPTION=n case.
>>
>> > What you really care about is the CONFIG_PREEMPTION=n case, but that you
>> > don't actually handle.
>>
>> I don't see that. The CONFIG_PREEMPTION=n (or its dynamic version)
>> is being handled here.
>
> Bah, I overlooked we have multiple definitions of the
> preempt_model_foo() things. For some reason I thought all that was only
> for DYNAMIC_PREEMPT.
>
>> > And yeah, you've got the extra resched_allowed() thing in there, but
>> > that doesn't make it any better -- this is all quite horrible.
>>
>> I don't disagree. There's a quite a lot of static/dynamic config options
>> here and adding this clause didn't improve things.
>>
>> I think just going with a static call here for the allow-resched case
>> might have been cleaner. Alternately I'll see if it can be cleanly
>> folded in with the irqentry_exit_cond_resched() logic.
>
> Something like the below perhaps?
>
> ---
> include/linux/entry-common.h | 6 ++++++
> kernel/entry/common.c | 23 +++++++++++++++++++++--
> 2 files changed, 27 insertions(+), 2 deletions(-)
>
> diff --git a/include/linux/entry-common.h b/include/linux/entry-common.h
> index d95ab85f96ba..0c365dc1f1c2 100644
> --- a/include/linux/entry-common.h
> +++ b/include/linux/entry-common.h
> @@ -415,10 +415,16 @@ irqentry_state_t noinstr irqentry_enter(struct pt_regs *regs);
> * Conditional reschedule with additional sanity checks.
> */
> void raw_irqentry_exit_cond_resched(void);
> +void irqentry_exit_cond_resched_tif(void);
> +
> #ifdef CONFIG_PREEMPT_DYNAMIC
> #if defined(CONFIG_HAVE_PREEMPT_DYNAMIC_CALL)
> #define irqentry_exit_cond_resched_dynamic_enabled raw_irqentry_exit_cond_resched
> +#ifdef TIF_RESCHED_ALLOW
> +#define irqentry_exit_cond_resched_dynamic_disabled irqentry_exit_cond_resched_tif
> +#else
> #define irqentry_exit_cond_resched_dynamic_disabled NULL
> +#endif
So this is clever. Essentially this would toggle between the two kinds
for the preempt_model_preemptible()/!preempt_model_preemptible() dynamic
case. Do I have that right?
> DECLARE_STATIC_CALL(irqentry_exit_cond_resched, raw_irqentry_exit_cond_resched);
> #define irqentry_exit_cond_resched() static_call(irqentry_exit_cond_resched)()
> #elif defined(CONFIG_HAVE_PREEMPT_DYNAMIC_KEY)
> diff --git a/kernel/entry/common.c b/kernel/entry/common.c
> index be61332c66b5..211d118aa672 100644
> --- a/kernel/entry/common.c
> +++ b/kernel/entry/common.c
> @@ -390,6 +390,21 @@ void raw_irqentry_exit_cond_resched(void)
> preempt_schedule_irq();
> }
> }
> +
> +void irqentry_exit_cond_resched_tif(void)
> +{
> +#ifdef TIF_RESCHED_ALLOW
> + if (resched_allowed()) {
> + /* Sanity check RCU and thread stack */
> + rcu_irq_exit_check_preempt();
> + if (IS_ENABLED(CONFIG_DEBUG_ENTRY))
> + WARN_ON_ONCE(!on_thread_stack());
> + if (need_resched())
> + preempt_schedule_irq();
> + }
> +#endif
> +}
> +
> #ifdef CONFIG_PREEMPT_DYNAMIC
> #if defined(CONFIG_HAVE_PREEMPT_DYNAMIC_CALL)
> DEFINE_STATIC_CALL(irqentry_exit_cond_resched, raw_irqentry_exit_cond_resched);
> @@ -397,8 +412,10 @@ DEFINE_STATIC_CALL(irqentry_exit_cond_resched, raw_irqentry_exit_cond_resched);
> DEFINE_STATIC_KEY_TRUE(sk_dynamic_irqentry_exit_cond_resched);
> void dynamic_irqentry_exit_cond_resched(void)
> {
> - if (!static_branch_unlikely(&sk_dynamic_irqentry_exit_cond_resched))
> - return;
> + if (!static_branch_unlikely(&sk_dynamic_irqentry_exit_cond_resched)) {
> + irqentry_exit_cond_resched_tif();
> + return
> + }
> raw_irqentry_exit_cond_resched();
> }
> #endif
> @@ -431,6 +448,8 @@ noinstr void irqentry_exit(struct pt_regs *regs, irqentry_state_t state)
> instrumentation_begin();
> if (IS_ENABLED(CONFIG_PREEMPTION))
> irqentry_exit_cond_resched();
> + else
> + irqentry_exit_cond_resched_tif();
And, if we choose between the two resched modes at compile time then this
would work.
Might massage the names a little but this should work as is. Okay if I
use your Codeveloped-by/Suggested-by on this patch?
--
ankur
On Thu, Apr 06, 2023 at 07:29:59PM -0700, Ankur Arora wrote:
> Peter Zijlstra <[email protected]> writes:
> > Something like the below perhaps?
> >
> > ---
> > include/linux/entry-common.h | 6 ++++++
> > kernel/entry/common.c | 23 +++++++++++++++++++++--
> > 2 files changed, 27 insertions(+), 2 deletions(-)
> >
> > diff --git a/include/linux/entry-common.h b/include/linux/entry-common.h
> > index d95ab85f96ba..0c365dc1f1c2 100644
> > --- a/include/linux/entry-common.h
> > +++ b/include/linux/entry-common.h
> > @@ -415,10 +415,16 @@ irqentry_state_t noinstr irqentry_enter(struct pt_regs *regs);
> > * Conditional reschedule with additional sanity checks.
> > */
> > void raw_irqentry_exit_cond_resched(void);
> > +void irqentry_exit_cond_resched_tif(void);
> > +
> > #ifdef CONFIG_PREEMPT_DYNAMIC
> > #if defined(CONFIG_HAVE_PREEMPT_DYNAMIC_CALL)
> > #define irqentry_exit_cond_resched_dynamic_enabled raw_irqentry_exit_cond_resched
> > +#ifdef TIF_RESCHED_ALLOW
> > +#define irqentry_exit_cond_resched_dynamic_disabled irqentry_exit_cond_resched_tif
> > +#else
> > #define irqentry_exit_cond_resched_dynamic_disabled NULL
> > +#endif
>
> So this is clever. Essentially this would toggle between the two kinds
> for the preempt_model_preemptible()/!preempt_model_preemptible() dynamic
> case. Do I have that right?
Exactly!
> > DECLARE_STATIC_CALL(irqentry_exit_cond_resched, raw_irqentry_exit_cond_resched);
> > #define irqentry_exit_cond_resched() static_call(irqentry_exit_cond_resched)()
> > #elif defined(CONFIG_HAVE_PREEMPT_DYNAMIC_KEY)
> > diff --git a/kernel/entry/common.c b/kernel/entry/common.c
> > index be61332c66b5..211d118aa672 100644
> > --- a/kernel/entry/common.c
> > +++ b/kernel/entry/common.c
> > @@ -390,6 +390,21 @@ void raw_irqentry_exit_cond_resched(void)
> > preempt_schedule_irq();
> > }
> > }
> > +
> > +void irqentry_exit_cond_resched_tif(void)
> > +{
> > +#ifdef TIF_RESCHED_ALLOW
> > + if (resched_allowed()) {
> > + /* Sanity check RCU and thread stack */
> > + rcu_irq_exit_check_preempt();
> > + if (IS_ENABLED(CONFIG_DEBUG_ENTRY))
> > + WARN_ON_ONCE(!on_thread_stack());
> > + if (need_resched())
> > + preempt_schedule_irq();
> > + }
> > +#endif
> > +}
> > +
> > #ifdef CONFIG_PREEMPT_DYNAMIC
> > #if defined(CONFIG_HAVE_PREEMPT_DYNAMIC_CALL)
> > DEFINE_STATIC_CALL(irqentry_exit_cond_resched, raw_irqentry_exit_cond_resched);
> > @@ -397,8 +412,10 @@ DEFINE_STATIC_CALL(irqentry_exit_cond_resched, raw_irqentry_exit_cond_resched);
> > DEFINE_STATIC_KEY_TRUE(sk_dynamic_irqentry_exit_cond_resched);
> > void dynamic_irqentry_exit_cond_resched(void)
> > {
> > - if (!static_branch_unlikely(&sk_dynamic_irqentry_exit_cond_resched))
> > - return;
> > + if (!static_branch_unlikely(&sk_dynamic_irqentry_exit_cond_resched)) {
> > + irqentry_exit_cond_resched_tif();
> > + return
> > + }
> > raw_irqentry_exit_cond_resched();
> > }
> > #endif
> > @@ -431,6 +448,8 @@ noinstr void irqentry_exit(struct pt_regs *regs, irqentry_state_t state)
> > instrumentation_begin();
> > if (IS_ENABLED(CONFIG_PREEMPTION))
> > irqentry_exit_cond_resched();
> > + else
> > + irqentry_exit_cond_resched_tif();
>
> And, if we choose between the two resched modes at compile time then this
> would work.
Just so.
> Might massage the names a little but this should work as is.
Yeah, I'm not liking the naming either, perhaps your
irqentry_exit_allow_resched() would've been better, dunno, see what
works.
> Okay if I use your Codeveloped-by/Suggested-by on this patch?
Yep.