Suspend to idle was found to not work on Goldmont CPU recently.
And the issue was triggered due to:
1. On Goldmont the CPU in idle can only be woken up via IPIs,
not POLL mode:
Commit 08e237fa56a1 ("x86/cpu: Add workaround for MONITOR
instruction erratum on Goldmont based CPUs")
2. When the CPU is entering suspend to idle process, the
_TIF_POLLING_NRFLAG is kept on.
3. Commit b2a02fc43a1f ("smp: Optimize send_call_function_single_ipi()")
makes use of _TIF_POLLING_NRFLAG to avoid sending IPIs to
idle CPUs.
4. As a result, some IPIs related functions might not work
well during suspend to idle on Goldmont. For example, one
suspected victim:
tick_unfreeze() -> timekeeping_resume() -> hrtimers_resume()
-> clock_was_set() -> on_each_cpu() might wait forever,
because the IPIs will not be sent to the CPUs which are
sleeping with _TIF_POLLING_NRFLAG set, and Goldmont CPU
could not be woken up by only setting _TIF_NEED_RESCHED
on the monitor address.
I don't find a way in Ubuntu to update the firmware of Goldmont
and check if the issue was gone, a fix patch would do no harm.
Clear the _TIF_POLLING_NRFLAG flag before entering suspend to idle,
and let the driver's enter_s2idle() to decide whether to set
_TIF_POLLING_NRFLAG or not. So that to avoid the scenario described
above and keep the context consistent with before.
Fixes: b2a02fc43a1f ("smp: Optimize send_call_function_single_ipi()")
Reported-by: kbuild test robot <[email protected]>
Cc: Peter Zijlstra (Intel) <[email protected]>
Signed-off-by: Chen Yu <[email protected]>
---
drivers/cpuidle/cpuidle.c | 5 ++++-
1 file changed, 4 insertions(+), 1 deletion(-)
diff --git a/drivers/cpuidle/cpuidle.c b/drivers/cpuidle/cpuidle.c
index c149d9e20dfd..d17dad362d34 100644
--- a/drivers/cpuidle/cpuidle.c
+++ b/drivers/cpuidle/cpuidle.c
@@ -13,6 +13,7 @@
#include <linux/mutex.h>
#include <linux/sched.h>
#include <linux/sched/clock.h>
+#include <linux/sched/idle.h>
#include <linux/notifier.h>
#include <linux/pm_qos.h>
#include <linux/cpu.h>
@@ -186,8 +187,10 @@ int cpuidle_enter_s2idle(struct cpuidle_driver *drv, struct cpuidle_device *dev)
* be frozen safely.
*/
index = find_deepest_state(drv, dev, U64_MAX, 0, true);
- if (index > 0)
+ if (index > 0) {
+ __current_clr_polling();
enter_s2idle_proper(drv, dev, index);
+ }
return index;
}
--
2.17.1
On Tue, Jun 16, 2020 at 01:36:11AM +0800, Chen Yu wrote:
> Suspend to idle was found to not work on Goldmont CPU recently.
> And the issue was triggered due to:
>
> 1. On Goldmont the CPU in idle can only be woken up via IPIs,
> not POLL mode:
> Commit 08e237fa56a1 ("x86/cpu: Add workaround for MONITOR
> instruction erratum on Goldmont based CPUs")
> 2. When the CPU is entering suspend to idle process, the
> _TIF_POLLING_NRFLAG is kept on.
> 3. Commit b2a02fc43a1f ("smp: Optimize send_call_function_single_ipi()")
> makes use of _TIF_POLLING_NRFLAG to avoid sending IPIs to
> idle CPUs.
> 4. As a result, some IPIs related functions might not work
> well during suspend to idle on Goldmont. For example, one
> suspected victim:
> tick_unfreeze() -> timekeeping_resume() -> hrtimers_resume()
> -> clock_was_set() -> on_each_cpu() might wait forever,
> because the IPIs will not be sent to the CPUs which are
> sleeping with _TIF_POLLING_NRFLAG set, and Goldmont CPU
> could not be woken up by only setting _TIF_NEED_RESCHED
> on the monitor address.
*sigh*... just what we need.
> @@ -186,8 +187,10 @@ int cpuidle_enter_s2idle(struct cpuidle_driver *drv, struct cpuidle_device *dev)
> * be frozen safely.
> */
> index = find_deepest_state(drv, dev, U64_MAX, 0, true);
> - if (index > 0)
> + if (index > 0) {
> + __current_clr_polling();
> enter_s2idle_proper(drv, dev, index);
> + }
>
> return index;
> }
So how is that commit 08e237fa56a1 not suffient? That makes
mwait_idle_with_hints() DTRT for this 'functionally challenged' piece of
hardware.
AFAICT intel_enter_s2idle() uses mwait_idle_with_hints().
What am I missing?
On Mon, Jun 15, 2020 at 08:40:41PM +0200, Peter Zijlstra wrote:
> > @@ -186,8 +187,10 @@ int cpuidle_enter_s2idle(struct cpuidle_driver *drv, struct cpuidle_device *dev)
> > * be frozen safely.
> > */
> > index = find_deepest_state(drv, dev, U64_MAX, 0, true);
> > - if (index > 0)
> > + if (index > 0) {
> > + __current_clr_polling();
> > enter_s2idle_proper(drv, dev, index);
> > + }
> >
> > return index;
> > }
>
> So how is that commit 08e237fa56a1 not suffient? That makes
> mwait_idle_with_hints() DTRT for this 'functionally challenged' piece of
> hardware.
>
> AFAICT intel_enter_s2idle() uses mwait_idle_with_hints().
>
> What am I missing?
What's missing is that cpuidle_enter_s2idle() doesn't properly match
call_cpuidle().
Something like so then. Your version is racy, if someone already set
TIF_NEED_RESCHED you just clear POLLING and go to sleep.
---
diff --git a/drivers/cpuidle/cpuidle.c b/drivers/cpuidle/cpuidle.c
index c149d9e20dfd..81bee8d03c6d 100644
--- a/drivers/cpuidle/cpuidle.c
+++ b/drivers/cpuidle/cpuidle.c
@@ -133,8 +133,8 @@ int cpuidle_find_deepest_state(struct cpuidle_driver *drv,
}
#ifdef CONFIG_SUSPEND
-static void enter_s2idle_proper(struct cpuidle_driver *drv,
- struct cpuidle_device *dev, int index)
+static void s2idle_enter(struct cpuidle_driver *drv,
+ struct cpuidle_device *dev, int index)
{
ktime_t time_start, time_end;
@@ -168,6 +168,15 @@ static void enter_s2idle_proper(struct cpuidle_driver *drv,
dev->states_usage[index].s2idle_usage++;
}
+static int call_s2idle(struct cpuidle_driver *drv, struct cpuidle_device *dev,
+ int index)
+{
+ if (!current_clr_polling_and_test())
+ s2idle_enter(drv, dev, index);
+
+ return index;
+}
+
/**
* cpuidle_enter_s2idle - Enter an idle state suitable for suspend-to-idle.
* @drv: cpuidle driver for the given CPU.
@@ -187,7 +196,7 @@ int cpuidle_enter_s2idle(struct cpuidle_driver *drv, struct cpuidle_device *dev)
*/
index = find_deepest_state(drv, dev, U64_MAX, 0, true);
if (index > 0)
- enter_s2idle_proper(drv, dev, index);
+ call_s2idle(drv, dev, index);
return index;
}
On Mon, Jun 15, 2020 at 09:31:54PM +0200, Peter Zijlstra wrote:
> On Mon, Jun 15, 2020 at 08:40:41PM +0200, Peter Zijlstra wrote:
>
> > > @@ -186,8 +187,10 @@ int cpuidle_enter_s2idle(struct cpuidle_driver *drv, struct cpuidle_device *dev)
> > > * be frozen safely.
> > > */
> > > index = find_deepest_state(drv, dev, U64_MAX, 0, true);
> > > - if (index > 0)
> > > + if (index > 0) {
> > > + __current_clr_polling();
> > > enter_s2idle_proper(drv, dev, index);
> > > + }
> > >
> > > return index;
> > > }
> >
> > So how is that commit 08e237fa56a1 not suffient? That makes
> > mwait_idle_with_hints() DTRT for this 'functionally challenged' piece of
> > hardware.
> >
> > AFAICT intel_enter_s2idle() uses mwait_idle_with_hints().
> >
> > What am I missing?
>
> What's missing is that cpuidle_enter_s2idle() doesn't properly match
> call_cpuidle().
>
Right.
> Something like so then. Your version is racy, if someone already set
> TIF_NEED_RESCHED you just clear POLLING and go to sleep.
>
Got it, I'll test the patch below.
Thanks,
Chenyu
> ---
>
> diff --git a/drivers/cpuidle/cpuidle.c b/drivers/cpuidle/cpuidle.c
> index c149d9e20dfd..81bee8d03c6d 100644
> --- a/drivers/cpuidle/cpuidle.c
> +++ b/drivers/cpuidle/cpuidle.c
> @@ -133,8 +133,8 @@ int cpuidle_find_deepest_state(struct cpuidle_driver *drv,
> }
>
> #ifdef CONFIG_SUSPEND
> -static void enter_s2idle_proper(struct cpuidle_driver *drv,
> - struct cpuidle_device *dev, int index)
> +static void s2idle_enter(struct cpuidle_driver *drv,
> + struct cpuidle_device *dev, int index)
> {
> ktime_t time_start, time_end;
>
> @@ -168,6 +168,15 @@ static void enter_s2idle_proper(struct cpuidle_driver *drv,
> dev->states_usage[index].s2idle_usage++;
> }
>
> +static int call_s2idle(struct cpuidle_driver *drv, struct cpuidle_device *dev,
> + int index)
> +{
> + if (!current_clr_polling_and_test())
> + s2idle_enter(drv, dev, index);
> +
> + return index;
> +}
> +
> /**
> * cpuidle_enter_s2idle - Enter an idle state suitable for suspend-to-idle.
> * @drv: cpuidle driver for the given CPU.
> @@ -187,7 +196,7 @@ int cpuidle_enter_s2idle(struct cpuidle_driver *drv, struct cpuidle_device *dev)
> */
> index = find_deepest_state(drv, dev, U64_MAX, 0, true);
> if (index > 0)
> - enter_s2idle_proper(drv, dev, index);
> + call_s2idle(drv, dev, index);
>
> return index;
> }