diff mbox series

[2/6] cpuidle: Introduce CPUIDLE_FLAG_MWAIT

Message ID 20250102150201.21639-3-frederic@kernel.org (mailing list archive)
State Changes Requested, archived
Headers show
Series cpuidle: Handle TIF_NR_POLLING on behalf of polling idle states | expand

Commit Message

Frederic Weisbecker Jan. 2, 2025, 3:01 p.m. UTC
From: Peter Zijlstra <peterz@infradead.org>

Provide a way to tell the cpuidle core about states monitoring
TIF_NEED_RESCHED on the hardware level, monitor/mwait users being the
only examples in use.

This will allow cpuidle core to manage TIF_NR_POLLING on behalf of all
kinds of TIF_NEED_RESCHED watching states while keeping a necessary
distinction for the governors between software loops polling on
TIF_NEED_RESCHED and hardware monitored writes to thread flags.

[fweisbec: _ Initialize flag from acpi_processor_setup_cstates() instead
             of acpi_processor_setup_lpi_states(), as the latter seem to
             be about arm64...
           _ Rename CPUIDLE_FLAG_NO_IPI to CPUIDLE_FLAG_MWAIT]

Signed-off-by: Peter Zijlstra <peterz@infradead.org>
Signed-off-by: Frederic Weisbecker <frederic@kernel.org>
---
 drivers/acpi/processor_idle.c | 3 +++
 drivers/idle/intel_idle.c     | 5 ++++-
 include/linux/cpuidle.h       | 1 +
 3 files changed, 8 insertions(+), 1 deletion(-)

Comments

Rafael J. Wysocki Jan. 14, 2025, 2:01 p.m. UTC | #1
On Thu, Jan 2, 2025 at 4:02 PM Frederic Weisbecker <frederic@kernel.org> wrote:
>
> From: Peter Zijlstra <peterz@infradead.org>
>
> Provide a way to tell the cpuidle core about states monitoring
> TIF_NEED_RESCHED on the hardware level, monitor/mwait users being the
> only examples in use.
>
> This will allow cpuidle core to manage TIF_NR_POLLING on behalf of all
> kinds of TIF_NEED_RESCHED watching states while keeping a necessary
> distinction for the governors between software loops polling on
> TIF_NEED_RESCHED and hardware monitored writes to thread flags.
>
> [fweisbec: _ Initialize flag from acpi_processor_setup_cstates() instead
>              of acpi_processor_setup_lpi_states(), as the latter seem to
>              be about arm64...
>            _ Rename CPUIDLE_FLAG_NO_IPI to CPUIDLE_FLAG_MWAIT]
>
> Signed-off-by: Peter Zijlstra <peterz@infradead.org>
> Signed-off-by: Frederic Weisbecker <frederic@kernel.org>
> ---
>  drivers/acpi/processor_idle.c | 3 +++
>  drivers/idle/intel_idle.c     | 5 ++++-
>  include/linux/cpuidle.h       | 1 +
>  3 files changed, 8 insertions(+), 1 deletion(-)
>
> diff --git a/drivers/acpi/processor_idle.c b/drivers/acpi/processor_idle.c
> index 698897b29de2..66cb5536d91e 100644
> --- a/drivers/acpi/processor_idle.c
> +++ b/drivers/acpi/processor_idle.c
> @@ -806,6 +806,9 @@ static int acpi_processor_setup_cstates(struct acpi_processor *pr)
>                 if (cx->type == ACPI_STATE_C1 || cx->type == ACPI_STATE_C2)
>                         drv->safe_state_index = count;
>
> +               if (cx->entry_method == ACPI_CSTATE_FFH)
> +                       state->flags |= CPUIDLE_FLAG_MWAIT;

FFH need not mean MWAIT in principle.

FFH in _CST means MWAIT in practice because _CST is used on x86 which
implements FFH through MWAIT, but it would be good at least to put a
comment here to explain that this code is only expected to run on x86.

Or better still, add something like acpi_arch_idle_state_flags(u8
entry_method) that will return CPUIDLE_FLAG_MWAIT for ACPI_CSTATE_FFH
and 0 otherwise and then do

    state->flags |= acpi_arch_idle_state_flags(cx->entry_method);

> +
>                 /*
>                  * Halt-induced C1 is not good for ->enter_s2idle, because it
>                  * re-enables interrupts on exit.  Moreover, C1 is generally not
> diff --git a/drivers/idle/intel_idle.c b/drivers/idle/intel_idle.c
> index ac4d8faa3886..d52723fbeb04 100644
> --- a/drivers/idle/intel_idle.c
> +++ b/drivers/idle/intel_idle.c
> @@ -1787,7 +1787,8 @@ static void __init intel_idle_init_cstates_acpi(struct cpuidle_driver *drv)
>                 if (cx->type > ACPI_STATE_C1)
>                         state->target_residency *= 3;
>
> -               state->flags = MWAIT2flg(cx->address);
> +               state->flags = MWAIT2flg(cx->address) | CPUIDLE_FLAG_MWAIT;
> +
>                 if (cx->type > ACPI_STATE_C2)
>                         state->flags |= CPUIDLE_FLAG_TLB_FLUSHED;
>
> @@ -2072,6 +2073,8 @@ static bool __init intel_idle_verify_cstate(unsigned int mwait_hint)
>
>  static void state_update_enter_method(struct cpuidle_state *state, int cstate)
>  {
> +       state->flags |= CPUIDLE_FLAG_MWAIT;
> +
>         if (state->flags & CPUIDLE_FLAG_INIT_XSTATE) {
>                 /*
>                  * Combining with XSTATE with IBRS or IRQ_ENABLE flags
> diff --git a/include/linux/cpuidle.h b/include/linux/cpuidle.h
> index a9ee4fe55dcf..b8084617aa27 100644
> --- a/include/linux/cpuidle.h
> +++ b/include/linux/cpuidle.h
> @@ -85,6 +85,7 @@ struct cpuidle_state {
>  #define CPUIDLE_FLAG_OFF               BIT(4) /* disable this state by default */
>  #define CPUIDLE_FLAG_TLB_FLUSHED       BIT(5) /* idle-state flushes TLBs */
>  #define CPUIDLE_FLAG_RCU_IDLE          BIT(6) /* idle-state takes care of RCU */
> +#define CPUIDLE_FLAG_MWAIT             BIT(7) /* hardware need_resched() monitoring */
>
>  struct cpuidle_device_kobj;
>  struct cpuidle_state_kobj;
> --
Sudeep Holla Jan. 14, 2025, 2:34 p.m. UTC | #2
On Tue, Jan 14, 2025 at 03:01:26PM +0100, Rafael J. Wysocki wrote:
> On Thu, Jan 2, 2025 at 4:02 PM Frederic Weisbecker <frederic@kernel.org> wrote:
> >
> > From: Peter Zijlstra <peterz@infradead.org>
> >
> > Provide a way to tell the cpuidle core about states monitoring
> > TIF_NEED_RESCHED on the hardware level, monitor/mwait users being the
> > only examples in use.
> >
> > This will allow cpuidle core to manage TIF_NR_POLLING on behalf of all
> > kinds of TIF_NEED_RESCHED watching states while keeping a necessary
> > distinction for the governors between software loops polling on
> > TIF_NEED_RESCHED and hardware monitored writes to thread flags.
> >
> > [fweisbec: _ Initialize flag from acpi_processor_setup_cstates() instead
> >              of acpi_processor_setup_lpi_states(), as the latter seem to
> >              be about arm64...
> >            _ Rename CPUIDLE_FLAG_NO_IPI to CPUIDLE_FLAG_MWAIT]
> >
> > Signed-off-by: Peter Zijlstra <peterz@infradead.org>
> > Signed-off-by: Frederic Weisbecker <frederic@kernel.org>
> > ---
> >  drivers/acpi/processor_idle.c | 3 +++
> >  drivers/idle/intel_idle.c     | 5 ++++-
> >  include/linux/cpuidle.h       | 1 +
> >  3 files changed, 8 insertions(+), 1 deletion(-)
> >
> > diff --git a/drivers/acpi/processor_idle.c b/drivers/acpi/processor_idle.c
> > index 698897b29de2..66cb5536d91e 100644
> > --- a/drivers/acpi/processor_idle.c
> > +++ b/drivers/acpi/processor_idle.c
> > @@ -806,6 +806,9 @@ static int acpi_processor_setup_cstates(struct acpi_processor *pr)
> >                 if (cx->type == ACPI_STATE_C1 || cx->type == ACPI_STATE_C2)
> >                         drv->safe_state_index = count;
> >
> > +               if (cx->entry_method == ACPI_CSTATE_FFH)
> > +                       state->flags |= CPUIDLE_FLAG_MWAIT;
> 
> FFH need not mean MWAIT in principle.
> 
> FFH in _CST means MWAIT in practice because _CST is used on x86 which
> implements FFH through MWAIT, but it would be good at least to put a
> comment here to explain that this code is only expected to run on x86.
> 
> Or better still, add something like acpi_arch_idle_state_flags(u8
> entry_method) that will return CPUIDLE_FLAG_MWAIT for ACPI_CSTATE_FFH
> and 0 otherwise and then do
> 
>     state->flags |= acpi_arch_idle_state_flags(cx->entry_method);
>

+1, was about to suggest the same. Though I am not aware of any Arm platforms
using C-States(LPI was added to suit Arm requirements), it is better to keep
the FFH definition arch specific.
Rafael J. Wysocki Jan. 14, 2025, 2:37 p.m. UTC | #3
On Tue, Jan 14, 2025 at 3:34 PM Sudeep Holla <sudeep.holla@arm.com> wrote:
>
> On Tue, Jan 14, 2025 at 03:01:26PM +0100, Rafael J. Wysocki wrote:
> > On Thu, Jan 2, 2025 at 4:02 PM Frederic Weisbecker <frederic@kernel.org> wrote:
> > >
> > > From: Peter Zijlstra <peterz@infradead.org>
> > >
> > > Provide a way to tell the cpuidle core about states monitoring
> > > TIF_NEED_RESCHED on the hardware level, monitor/mwait users being the
> > > only examples in use.
> > >
> > > This will allow cpuidle core to manage TIF_NR_POLLING on behalf of all
> > > kinds of TIF_NEED_RESCHED watching states while keeping a necessary
> > > distinction for the governors between software loops polling on
> > > TIF_NEED_RESCHED and hardware monitored writes to thread flags.
> > >
> > > [fweisbec: _ Initialize flag from acpi_processor_setup_cstates() instead
> > >              of acpi_processor_setup_lpi_states(), as the latter seem to
> > >              be about arm64...
> > >            _ Rename CPUIDLE_FLAG_NO_IPI to CPUIDLE_FLAG_MWAIT]
> > >
> > > Signed-off-by: Peter Zijlstra <peterz@infradead.org>
> > > Signed-off-by: Frederic Weisbecker <frederic@kernel.org>
> > > ---
> > >  drivers/acpi/processor_idle.c | 3 +++
> > >  drivers/idle/intel_idle.c     | 5 ++++-
> > >  include/linux/cpuidle.h       | 1 +
> > >  3 files changed, 8 insertions(+), 1 deletion(-)
> > >
> > > diff --git a/drivers/acpi/processor_idle.c b/drivers/acpi/processor_idle.c
> > > index 698897b29de2..66cb5536d91e 100644
> > > --- a/drivers/acpi/processor_idle.c
> > > +++ b/drivers/acpi/processor_idle.c
> > > @@ -806,6 +806,9 @@ static int acpi_processor_setup_cstates(struct acpi_processor *pr)
> > >                 if (cx->type == ACPI_STATE_C1 || cx->type == ACPI_STATE_C2)
> > >                         drv->safe_state_index = count;
> > >
> > > +               if (cx->entry_method == ACPI_CSTATE_FFH)
> > > +                       state->flags |= CPUIDLE_FLAG_MWAIT;
> >
> > FFH need not mean MWAIT in principle.
> >
> > FFH in _CST means MWAIT in practice because _CST is used on x86 which
> > implements FFH through MWAIT, but it would be good at least to put a
> > comment here to explain that this code is only expected to run on x86.
> >
> > Or better still, add something like acpi_arch_idle_state_flags(u8
> > entry_method) that will return CPUIDLE_FLAG_MWAIT for ACPI_CSTATE_FFH
> > and 0 otherwise and then do
> >
> >     state->flags |= acpi_arch_idle_state_flags(cx->entry_method);
> >
>
> +1, was about to suggest the same. Though I am not aware of any Arm platforms
> using C-States(LPI was added to suit Arm requirements), it is better to keep
> the FFH definition arch specific.

Which will be consistent with this patch among other things:

https://lore.kernel.org/linux-pm/20250110115953.6058-3-patryk.wlazlyn@linux.intel.com/
diff mbox series

Patch

diff --git a/drivers/acpi/processor_idle.c b/drivers/acpi/processor_idle.c
index 698897b29de2..66cb5536d91e 100644
--- a/drivers/acpi/processor_idle.c
+++ b/drivers/acpi/processor_idle.c
@@ -806,6 +806,9 @@  static int acpi_processor_setup_cstates(struct acpi_processor *pr)
 		if (cx->type == ACPI_STATE_C1 || cx->type == ACPI_STATE_C2)
 			drv->safe_state_index = count;
 
+		if (cx->entry_method == ACPI_CSTATE_FFH)
+			state->flags |= CPUIDLE_FLAG_MWAIT;
+
 		/*
 		 * Halt-induced C1 is not good for ->enter_s2idle, because it
 		 * re-enables interrupts on exit.  Moreover, C1 is generally not
diff --git a/drivers/idle/intel_idle.c b/drivers/idle/intel_idle.c
index ac4d8faa3886..d52723fbeb04 100644
--- a/drivers/idle/intel_idle.c
+++ b/drivers/idle/intel_idle.c
@@ -1787,7 +1787,8 @@  static void __init intel_idle_init_cstates_acpi(struct cpuidle_driver *drv)
 		if (cx->type > ACPI_STATE_C1)
 			state->target_residency *= 3;
 
-		state->flags = MWAIT2flg(cx->address);
+		state->flags = MWAIT2flg(cx->address) | CPUIDLE_FLAG_MWAIT;
+
 		if (cx->type > ACPI_STATE_C2)
 			state->flags |= CPUIDLE_FLAG_TLB_FLUSHED;
 
@@ -2072,6 +2073,8 @@  static bool __init intel_idle_verify_cstate(unsigned int mwait_hint)
 
 static void state_update_enter_method(struct cpuidle_state *state, int cstate)
 {
+	state->flags |= CPUIDLE_FLAG_MWAIT;
+
 	if (state->flags & CPUIDLE_FLAG_INIT_XSTATE) {
 		/*
 		 * Combining with XSTATE with IBRS or IRQ_ENABLE flags
diff --git a/include/linux/cpuidle.h b/include/linux/cpuidle.h
index a9ee4fe55dcf..b8084617aa27 100644
--- a/include/linux/cpuidle.h
+++ b/include/linux/cpuidle.h
@@ -85,6 +85,7 @@  struct cpuidle_state {
 #define CPUIDLE_FLAG_OFF		BIT(4) /* disable this state by default */
 #define CPUIDLE_FLAG_TLB_FLUSHED	BIT(5) /* idle-state flushes TLBs */
 #define CPUIDLE_FLAG_RCU_IDLE		BIT(6) /* idle-state takes care of RCU */
+#define CPUIDLE_FLAG_MWAIT		BIT(7) /* hardware need_resched() monitoring */
 
 struct cpuidle_device_kobj;
 struct cpuidle_state_kobj;