diff mbox series

[v4,7/8] cpuidle/poll_state: replace cpu_relax with smp_cond_load_relaxed

Message ID 1707982910-27680-8-git-send-email-mihai.carabas@oracle.com (mailing list archive)
State New, archived
Headers show
Series [v4,1/8] x86: Move ARCH_HAS_CPU_RELAX to arch | expand

Commit Message

Mihai Carabas Feb. 15, 2024, 7:41 a.m. UTC
cpu_relax on ARM64 does a simple "yield". Thus we replace it with
smp_cond_load_relaxed which basically does a "wfe".

Suggested-by: Peter Zijlstra <peterz@infradead.org>
Signed-off-by: Mihai Carabas <mihai.carabas@oracle.com>
---
 drivers/cpuidle/poll_state.c | 15 ++++++++++-----
 1 file changed, 10 insertions(+), 5 deletions(-)

Comments

Tomohiro Misono (Fujitsu) Feb. 26, 2024, 8:36 a.m. UTC | #1
Hi,
> Subject: [PATCH v4 7/8] cpuidle/poll_state: replace cpu_relax with smp_cond_load_relaxed
> 
> cpu_relax on ARM64 does a simple "yield". Thus we replace it with
> smp_cond_load_relaxed which basically does a "wfe".
> 
> Suggested-by: Peter Zijlstra <peterz@infradead.org>
> Signed-off-by: Mihai Carabas <mihai.carabas@oracle.com>
> ---
>  drivers/cpuidle/poll_state.c | 15 ++++++++++-----
>  1 file changed, 10 insertions(+), 5 deletions(-)
> 
> diff --git a/drivers/cpuidle/poll_state.c b/drivers/cpuidle/poll_state.c
> index 9b6d90a72601..1e45be906e72 100644
> --- a/drivers/cpuidle/poll_state.c
> +++ b/drivers/cpuidle/poll_state.c
> @@ -13,6 +13,7 @@
>  static int __cpuidle poll_idle(struct cpuidle_device *dev,
>  			       struct cpuidle_driver *drv, int index)
>  {
> +	unsigned long ret;
>  	u64 time_start;
> 
>  	time_start = local_clock_noinstr();
> @@ -26,12 +27,16 @@ static int __cpuidle poll_idle(struct cpuidle_device *dev,
> 
>  		limit = cpuidle_poll_time(drv, dev);
> 
> -		while (!need_resched()) {
> -			cpu_relax();
> -			if (loop_count++ < POLL_IDLE_RELAX_COUNT)
> -				continue;
> -
> +		for (;;) {
>  			loop_count = 0;
> +
> +			ret = smp_cond_load_relaxed(&current_thread_info()->flags,
> +						    VAL & _TIF_NEED_RESCHED ||
> +						    loop_count++ >= POLL_IDLE_RELAX_COUNT);
> +
> +			if (!(ret & _TIF_NEED_RESCHED))
> +				break;

Should this be "if (ret & _TIF_NEED_RESCHED) since we want to break here
if the flag is set, or am I misunderstood?

Regards,
Tomohiro

> +
>  			if (local_clock_noinstr() - time_start > limit) {
>  				dev->poll_time_limit = true;
>  				break;
> --
> 1.8.3.1
> 
> 
> _______________________________________________
> linux-arm-kernel mailing list
> linux-arm-kernel@lists.infradead.org
> http://lists.infradead.org/mailman/listinfo/linux-arm-kernel
Ankur Arora Feb. 28, 2024, 4:36 a.m. UTC | #2
Tomohiro Misono (Fujitsu) <misono.tomohiro@fujitsu.com> writes:

> Hi,
> > Subject: [PATCH v4 7/8] cpuidle/poll_state: replace cpu_relax with smp_cond_load_relaxed
> > 
> > cpu_relax on ARM64 does a simple "yield". Thus we replace it with
> > smp_cond_load_relaxed which basically does a "wfe".
> >
> > Suggested-by: Peter Zijlstra <peterz@infradead.org>
> > Signed-off-by: Mihai Carabas <mihai.carabas@oracle.com>
> > ---
> >  drivers/cpuidle/poll_state.c | 15 ++++++++++-----
> >  1 file changed, 10 insertions(+), 5 deletions(-)
> >
> > diff --git a/drivers/cpuidle/poll_state.c b/drivers/cpuidle/poll_state.c
> > index 9b6d90a72601..1e45be906e72 100644
> > --- a/drivers/cpuidle/poll_state.c
> > +++ b/drivers/cpuidle/poll_state.c
> > @@ -13,6 +13,7 @@
> >  static int __cpuidle poll_idle(struct cpuidle_device *dev,
> >                              struct cpuidle_driver *drv, int index)
> >  {
> > +     unsigned long ret;
> >       u64 time_start;
> >
> >       time_start = local_clock_noinstr();
> > @@ -26,12 +27,16 @@ static int __cpuidle poll_idle(struct cpuidle_device *dev,
> >
> >               limit = cpuidle_poll_time(drv, dev);
> >
> > -             while (!need_resched()) {
> > -                     cpu_relax();
> > -                     if (loop_count++ < POLL_IDLE_RELAX_COUNT)
> > -                             continue;
> > -
> > +             for (;;) {
> >                       loop_count = 0;
> > +
> > +                     ret = smp_cond_load_relaxed(&current_thread_info()->flags,
> > +                                                 VAL & _TIF_NEED_RESCHED ||
> > +                                                 loop_count++ >= POLL_IDLE_RELAX_COUNT);
> > +
> > +                     if (!(ret & _TIF_NEED_RESCHED))
> > +                             break;
> 
> Should this be "if (ret & _TIF_NEED_RESCHED) since we want to break here
> if the flag is set, or am I misunderstood?

Yeah, you are right. The check is inverted.

I'll be re-spinning this series. Will fix. Though, it probably makes sense
to just keep the original "while (!need_resched())" check.

Thanks for the review.

--
ankur
Okanovic, Haris April 5, 2024, 9:51 p.m. UTC | #3
On Thu, 2024-02-15 at 09:41 +0200, Mihai Carabas wrote:
> cpu_relax on ARM64 does a simple "yield". Thus we replace it with
> smp_cond_load_relaxed which basically does a "wfe".
> 
> Suggested-by: Peter Zijlstra <peterz@infradead.org>
> Signed-off-by: Mihai Carabas <mihai.carabas@oracle.com>
> ---
>  drivers/cpuidle/poll_state.c | 15 ++++++++++-----
>  1 file changed, 10 insertions(+), 5 deletions(-)
> 
> diff --git a/drivers/cpuidle/poll_state.c b/drivers/cpuidle/poll_state.c
> index 9b6d90a72601..1e45be906e72 100644
> --- a/drivers/cpuidle/poll_state.c
> +++ b/drivers/cpuidle/poll_state.c
> @@ -13,6 +13,7 @@
>  static int __cpuidle poll_idle(struct cpuidle_device *dev,
>  			       struct cpuidle_driver *drv, int index)
>  {
> +	unsigned long ret;
>  	u64 time_start;
>  
>  	time_start = local_clock_noinstr();
> @@ -26,12 +27,16 @@ static int __cpuidle poll_idle(struct cpuidle_device *dev,
>  
>  		limit = cpuidle_poll_time(drv, dev);
>  
> -		while (!need_resched()) {
> -			cpu_relax();
> -			if (loop_count++ < POLL_IDLE_RELAX_COUNT)
> -				continue;
> -
> +		for (;;) {
>  			loop_count = 0;
> +
> +			ret = smp_cond_load_relaxed(&current_thread_info()->flags,
> +						    VAL & _TIF_NEED_RESCHED ||
> +						    loop_count++ >= POLL_IDLE_RELAX_COUNT);

Is it necessary to repeat this 200 times with a wfe poll? Does kvm not
implement a timeout period?

Could you make it configurable? This patch improves certain workloads
on AWS Graviton instances as well, but blocks up to 6ms in 200 * 30us
increments before going to wfi, which is a bit excessive.

> +
> +			if (!(ret & _TIF_NEED_RESCHED))
> +				break;
> +
>  			if (local_clock_noinstr() - time_start > limit) {
>  				dev->poll_time_limit = true;
>  				break;
Ankur Arora April 5, 2024, 11:14 p.m. UTC | #4
Okanovic, Haris <harisokn@amazon.com> writes:

> On Thu, 2024-02-15 at 09:41 +0200, Mihai Carabas wrote:
>> cpu_relax on ARM64 does a simple "yield". Thus we replace it with
>> smp_cond_load_relaxed which basically does a "wfe".
>>
>> Suggested-by: Peter Zijlstra <peterz@infradead.org>
>> Signed-off-by: Mihai Carabas <mihai.carabas@oracle.com>
>> ---
>>  drivers/cpuidle/poll_state.c | 15 ++++++++++-----
>>  1 file changed, 10 insertions(+), 5 deletions(-)
>>
>> diff --git a/drivers/cpuidle/poll_state.c b/drivers/cpuidle/poll_state.c
>> index 9b6d90a72601..1e45be906e72 100644
>> --- a/drivers/cpuidle/poll_state.c
>> +++ b/drivers/cpuidle/poll_state.c
>> @@ -13,6 +13,7 @@
>>  static int __cpuidle poll_idle(struct cpuidle_device *dev,
>>  			       struct cpuidle_driver *drv, int index)
>>  {
>> +	unsigned long ret;
>>  	u64 time_start;
>>
>>  	time_start = local_clock_noinstr();
>> @@ -26,12 +27,16 @@ static int __cpuidle poll_idle(struct cpuidle_device *dev,
>>
>>  		limit = cpuidle_poll_time(drv, dev);
>>
>> -		while (!need_resched()) {
>> -			cpu_relax();
>> -			if (loop_count++ < POLL_IDLE_RELAX_COUNT)
>> -				continue;
>> -
>> +		for (;;) {
>>  			loop_count = 0;
>> +
>> +			ret = smp_cond_load_relaxed(&current_thread_info()->flags,
>> +						    VAL & _TIF_NEED_RESCHED ||
>> +						    loop_count++ >= POLL_IDLE_RELAX_COUNT);
>
> Is it necessary to repeat this 200 times with a wfe poll?

The POLL_IDLE_RELAX_COUNT is there because on x86 each cpu_relax()
iteration is much shorter.

With WFE, it makes less sense.

> Does kvm not implement a timeout period?

Not yet, but it does become more useful after a WFE haltpoll is
available on ARM64.

Haltpoll does have a timeout, which you should be able to tune via
/sys/module/haltpoll/parameters/ but that, of course, won't help here.

> Could you make it configurable? This patch improves certain workloads
> on AWS Graviton instances as well, but blocks up to 6ms in 200 * 30us
> increments before going to wfi, which is a bit excessive.

Yeah, this looks like a problem. We could solve it by making it an
architectural parameter. Though I worry about ARM platforms with
much smaller default timeouts.
The other possibility is using WFET in the primitive, but then we
have that dependency and that's a bigger change.

Will address this in the next version.

Thanks for pointing this out.

--
ankur
Okanovic, Haris April 6, 2024, 6:42 p.m. UTC | #5
On Fri, 2024-04-05 at 16:14 -0700, Ankur Arora wrote:
> CAUTION: This email originated from outside of the organization. Do not click links or open attachments unless you can confirm the sender and know the content is safe.
> 
> 
> 
> Okanovic, Haris <harisokn@amazon.com> writes:
> 
> > On Thu, 2024-02-15 at 09:41 +0200, Mihai Carabas wrote:
> > > cpu_relax on ARM64 does a simple "yield". Thus we replace it with
> > > smp_cond_load_relaxed which basically does a "wfe".
> > > 
> > > Suggested-by: Peter Zijlstra <peterz@infradead.org>
> > > Signed-off-by: Mihai Carabas <mihai.carabas@oracle.com>
> > > ---
> > >  drivers/cpuidle/poll_state.c | 15 ++++++++++-----
> > >  1 file changed, 10 insertions(+), 5 deletions(-)
> > > 
> > > diff --git a/drivers/cpuidle/poll_state.c b/drivers/cpuidle/poll_state.c
> > > index 9b6d90a72601..1e45be906e72 100644
> > > --- a/drivers/cpuidle/poll_state.c
> > > +++ b/drivers/cpuidle/poll_state.c
> > > @@ -13,6 +13,7 @@
> > >  static int __cpuidle poll_idle(struct cpuidle_device *dev,
> > >                             struct cpuidle_driver *drv, int index)
> > >  {
> > > +    unsigned long ret;
> > >      u64 time_start;
> > > 
> > >      time_start = local_clock_noinstr();
> > > @@ -26,12 +27,16 @@ static int __cpuidle poll_idle(struct cpuidle_device *dev,
> > > 
> > >              limit = cpuidle_poll_time(drv, dev);
> > > 
> > > -            while (!need_resched()) {
> > > -                    cpu_relax();
> > > -                    if (loop_count++ < POLL_IDLE_RELAX_COUNT)
> > > -                            continue;
> > > -
> > > +            for (;;) {
> > >                      loop_count = 0;
> > > +
> > > +                    ret = smp_cond_load_relaxed(&current_thread_info()->flags,
> > > +                                                VAL & _TIF_NEED_RESCHED ||
> > > +                                                loop_count++ >= POLL_IDLE_RELAX_COUNT);
> > 
> > Is it necessary to repeat this 200 times with a wfe poll?
> 
> The POLL_IDLE_RELAX_COUNT is there because on x86 each cpu_relax()
> iteration is much shorter.
> 
> With WFE, it makes less sense.
> 
> > Does kvm not implement a timeout period?
> 
> Not yet, but it does become more useful after a WFE haltpoll is
> available on ARM64.

Note that kvm conditionally traps WFE and WFI based on number of host
CPU tasks. VMs will sometimes see hardware behavior - potentially
polling for a long time before entering WFI.

https://elixir.bootlin.com/linux/latest/source/arch/arm64/kvm/arm.c#L459

> 
> Haltpoll does have a timeout, which you should be able to tune via
> /sys/module/haltpoll/parameters/ but that, of course, won't help here.
> 
> > Could you make it configurable? This patch improves certain workloads
> > on AWS Graviton instances as well, but blocks up to 6ms in 200 * 30us
> > increments before going to wfi, which is a bit excessive.
> 
> Yeah, this looks like a problem. We could solve it by making it an
> architectural parameter. Though I worry about ARM platforms with
> much smaller default timeouts.
> The other possibility is using WFET in the primitive, but then we
> have that dependency and that's a bigger change.

See arm64's delay() for inspiration:

https://elixir.bootlin.com/linux/v6.9-rc2/source/arch/arm64/lib/delay.c#L26

> 
> Will address this in the next version.
> 
> Thanks for pointing this out.
> 
> --
> ankur
Ankur Arora April 8, 2024, 6:46 p.m. UTC | #6
Okanovic, Haris <harisokn@amazon.com> writes:

> On Fri, 2024-04-05 at 16:14 -0700, Ankur Arora wrote:
>> CAUTION: This email originated from outside of the organization. Do not click links or open attachments unless you can confirm the sender and know the content is safe.
>>
>>
>>
>> Okanovic, Haris <harisokn@amazon.com> writes:
>>
>> > On Thu, 2024-02-15 at 09:41 +0200, Mihai Carabas wrote:
>> > > cpu_relax on ARM64 does a simple "yield". Thus we replace it with
>> > > smp_cond_load_relaxed which basically does a "wfe".
>> > >
>> > > Suggested-by: Peter Zijlstra <peterz@infradead.org>
>> > > Signed-off-by: Mihai Carabas <mihai.carabas@oracle.com>
>> > > ---
>> > >  drivers/cpuidle/poll_state.c | 15 ++++++++++-----
>> > >  1 file changed, 10 insertions(+), 5 deletions(-)
>> > >
>> > > diff --git a/drivers/cpuidle/poll_state.c b/drivers/cpuidle/poll_state.c
>> > > index 9b6d90a72601..1e45be906e72 100644
>> > > --- a/drivers/cpuidle/poll_state.c
>> > > +++ b/drivers/cpuidle/poll_state.c
>> > > @@ -13,6 +13,7 @@
>> > >  static int __cpuidle poll_idle(struct cpuidle_device *dev,
>> > >                             struct cpuidle_driver *drv, int index)
>> > >  {
>> > > +    unsigned long ret;
>> > >      u64 time_start;
>> > >
>> > >      time_start = local_clock_noinstr();
>> > > @@ -26,12 +27,16 @@ static int __cpuidle poll_idle(struct cpuidle_device *dev,
>> > >
>> > >              limit = cpuidle_poll_time(drv, dev);
>> > >
>> > > -            while (!need_resched()) {
>> > > -                    cpu_relax();
>> > > -                    if (loop_count++ < POLL_IDLE_RELAX_COUNT)
>> > > -                            continue;
>> > > -
>> > > +            for (;;) {
>> > >                      loop_count = 0;
>> > > +
>> > > +                    ret = smp_cond_load_relaxed(&current_thread_info()->flags,
>> > > +                                                VAL & _TIF_NEED_RESCHED ||
>> > > +                                                loop_count++ >= POLL_IDLE_RELAX_COUNT);
>> >
>> > Is it necessary to repeat this 200 times with a wfe poll?
>>
>> The POLL_IDLE_RELAX_COUNT is there because on x86 each cpu_relax()
>> iteration is much shorter.
>>
>> With WFE, it makes less sense.
>>
>> > Does kvm not implement a timeout period?
>>
>> Not yet, but it does become more useful after a WFE haltpoll is
>> available on ARM64.
>
> Note that kvm conditionally traps WFE and WFI based on number of host
> CPU tasks. VMs will sometimes see hardware behavior - potentially
> polling for a long time before entering WFI.
>
> https://elixir.bootlin.com/linux/latest/source/arch/arm64/kvm/arm.c#L459

Yeah. There was a discussion on this
https://lore.kernel.org/lkml/871qc6qufy.fsf@oracle.com/.

>> Haltpoll does have a timeout, which you should be able to tune via
>> /sys/module/haltpoll/parameters/ but that, of course, won't help here.
>>
>> > Could you make it configurable? This patch improves certain workloads
>> > on AWS Graviton instances as well, but blocks up to 6ms in 200 * 30us
>> > increments before going to wfi, which is a bit excessive.
>>
>> Yeah, this looks like a problem. We could solve it by making it an
>> architectural parameter. Though I worry about ARM platforms with
>> much smaller default timeouts.
>> The other possibility is using WFET in the primitive, but then we
>> have that dependency and that's a bigger change.
>
> See arm64's delay() for inspiration:
>
> https://elixir.bootlin.com/linux/v6.9-rc2/source/arch/arm64/lib/delay.c#L26

Sure, that part is straight-forward enough. However, this will need a fallback
the case when WFET is not available. And, because this path is used on x86,
so we need a cross platform smp_cond*timeout(). Though given that the x86
version is based on cpu_relax() then that could just fold the sched_clock()
check in.

Maybe another place to do this would be by KVM forcing a WFE timeout. Arguably
that is needed regardless of whether we use a smp_cond*timeout() or not.

--
ankur
Okanovic, Haris April 8, 2024, 8:04 p.m. UTC | #7
On Mon, 2024-04-08 at 11:46 -0700, Ankur Arora wrote:
> CAUTION: This email originated from outside of the organization. Do not click links or open attachments unless you can confirm the sender and know the content is safe.
> 
> 
> 
> Okanovic, Haris <harisokn@amazon.com> writes:
> 
> > On Fri, 2024-04-05 at 16:14 -0700, Ankur Arora wrote:
> > > CAUTION: This email originated from outside of the organization. Do not click links or open attachments unless you can confirm the sender and know the content is safe.
> > > 
> > > 
> > > 
> > > Okanovic, Haris <harisokn@amazon.com> writes:
> > > 
> > > > On Thu, 2024-02-15 at 09:41 +0200, Mihai Carabas wrote:
> > > > > cpu_relax on ARM64 does a simple "yield". Thus we replace it with
> > > > > smp_cond_load_relaxed which basically does a "wfe".
> > > > > 
> > > > > Suggested-by: Peter Zijlstra <peterz@infradead.org>
> > > > > Signed-off-by: Mihai Carabas <mihai.carabas@oracle.com>
> > > > > ---
> > > > >  drivers/cpuidle/poll_state.c | 15 ++++++++++-----
> > > > >  1 file changed, 10 insertions(+), 5 deletions(-)
> > > > > 
> > > > > diff --git a/drivers/cpuidle/poll_state.c b/drivers/cpuidle/poll_state.c
> > > > > index 9b6d90a72601..1e45be906e72 100644
> > > > > --- a/drivers/cpuidle/poll_state.c
> > > > > +++ b/drivers/cpuidle/poll_state.c
> > > > > @@ -13,6 +13,7 @@
> > > > >  static int __cpuidle poll_idle(struct cpuidle_device *dev,
> > > > >                             struct cpuidle_driver *drv, int index)
> > > > >  {
> > > > > +    unsigned long ret;
> > > > >      u64 time_start;
> > > > > 
> > > > >      time_start = local_clock_noinstr();
> > > > > @@ -26,12 +27,16 @@ static int __cpuidle poll_idle(struct cpuidle_device *dev,
> > > > > 
> > > > >              limit = cpuidle_poll_time(drv, dev);
> > > > > 
> > > > > -            while (!need_resched()) {
> > > > > -                    cpu_relax();
> > > > > -                    if (loop_count++ < POLL_IDLE_RELAX_COUNT)
> > > > > -                            continue;
> > > > > -
> > > > > +            for (;;) {
> > > > >                      loop_count = 0;
> > > > > +
> > > > > +                    ret = smp_cond_load_relaxed(&current_thread_info()->flags,
> > > > > +                                                VAL & _TIF_NEED_RESCHED ||
> > > > > +                                                loop_count++ >= POLL_IDLE_RELAX_COUNT);
> > > > 
> > > > Is it necessary to repeat this 200 times with a wfe poll?
> > > 
> > > The POLL_IDLE_RELAX_COUNT is there because on x86 each cpu_relax()
> > > iteration is much shorter.
> > > 
> > > With WFE, it makes less sense.
> > > 
> > > > Does kvm not implement a timeout period?
> > > 
> > > Not yet, but it does become more useful after a WFE haltpoll is
> > > available on ARM64.
> > 
> > Note that kvm conditionally traps WFE and WFI based on number of host
> > CPU tasks. VMs will sometimes see hardware behavior - potentially
> > polling for a long time before entering WFI.
> > 
> > https://elixir.bootlin.com/linux/latest/source/arch/arm64/kvm/arm.c#L459
> 
> Yeah. There was a discussion on this
> https://lore.kernel.org/lkml/871qc6qufy.fsf@oracle.com/.
> 
> > > Haltpoll does have a timeout, which you should be able to tune via
> > > /sys/module/haltpoll/parameters/ but that, of course, won't help here.
> > > 
> > > > Could you make it configurable? This patch improves certain workloads
> > > > on AWS Graviton instances as well, but blocks up to 6ms in 200 * 30us
> > > > increments before going to wfi, which is a bit excessive.
> > > 
> > > Yeah, this looks like a problem. We could solve it by making it an
> > > architectural parameter. Though I worry about ARM platforms with
> > > much smaller default timeouts.
> > > The other possibility is using WFET in the primitive, but then we
> > > have that dependency and that's a bigger change.
> > 
> > See arm64's delay() for inspiration:
> > 
> > https://elixir.bootlin.com/linux/v6.9-rc2/source/arch/arm64/lib/delay.c#L26
> 
> Sure, that part is straight-forward enough. However, this will need a fallback
> the case when WFET is not available. And, because this path is used on x86,
> so we need a cross platform smp_cond*timeout(). Though given that the x86
> version is based on cpu_relax() then that could just fold the sched_clock()
> check in.

I was trying to point out how delay() handles different configurations:
It prefers WFET when available, falls back to WFE when event stream is
available, and finally falls back to cpu_relax() as last resort. Same
logic can apply here. The x86 case can always use cpu_relax() fallback,
for same behavior as smp_cond_load_relaxed().

Re your concern about "ARM platforms with much smaller default
timeouts": You could do something different when arch_timer_get_rate()
is too small. Although I'm not sure this is a huge concern, given that
delay() doesn't seem to care in the WFE case.

-- Haris Okanovic

> 
> Maybe another place to do this would be by KVM forcing a WFE timeout. Arguably
> that is needed regardless of whether we use a smp_cond*timeout() or not.
> 
> --
> ankur
diff mbox series

Patch

diff --git a/drivers/cpuidle/poll_state.c b/drivers/cpuidle/poll_state.c
index 9b6d90a72601..1e45be906e72 100644
--- a/drivers/cpuidle/poll_state.c
+++ b/drivers/cpuidle/poll_state.c
@@ -13,6 +13,7 @@ 
 static int __cpuidle poll_idle(struct cpuidle_device *dev,
 			       struct cpuidle_driver *drv, int index)
 {
+	unsigned long ret;
 	u64 time_start;
 
 	time_start = local_clock_noinstr();
@@ -26,12 +27,16 @@  static int __cpuidle poll_idle(struct cpuidle_device *dev,
 
 		limit = cpuidle_poll_time(drv, dev);
 
-		while (!need_resched()) {
-			cpu_relax();
-			if (loop_count++ < POLL_IDLE_RELAX_COUNT)
-				continue;
-
+		for (;;) {
 			loop_count = 0;
+
+			ret = smp_cond_load_relaxed(&current_thread_info()->flags,
+						    VAL & _TIF_NEED_RESCHED ||
+						    loop_count++ >= POLL_IDLE_RELAX_COUNT);
+
+			if (!(ret & _TIF_NEED_RESCHED))
+				break;
+
 			if (local_clock_noinstr() - time_start > limit) {
 				dev->poll_time_limit = true;
 				break;