[PATCH 0/2] clockevents: Hide CLOCK_EVT_STATE_* from rest of the kernel

[PATCH 0/2] clockevents: Hide CLOCK_EVT_STATE_* from rest of the kernel

[Viresh Kumar]

Hi Thomas,

Ingo suggested [1] to keep CLOCK_EVT_STATE_* symbols somewhere in
kernel/time/. We couldn't do it as bL_switcher code was using it
earlier. But that's fixed now. And so the first patch moves these
symbols to tick-internal.h.

Some of the drivers [2] need to verify state of the clockevent device
from their callbacks or interrupt handlers.

Because these symbols (defined by 'enum clock_event_state') will now be
internal to the core, we need some helpers to verify state of a
clockevent device.

One way out was to maintain the state in drivers as well, but that would
be unnecessary burden on them. And so the second patch introduces
helpers for these states.

Rebased-over: tip/timers/core (dependency on 8fff52fd5093 ("clockevents:
Introduce CLOCK_EVT_STATE_ONESHOT_STOPPED state"))

--
viresh

[1] https://lists.linaro.org/pipermail/linaro-kernel/2015-February/020292.html
[2] http://pastebin.com/374X18mv

Viresh Kumar (2):
  clockevents: Move 'enum clock_event_state' to tick-internal.h
  clockevents: Add helpers to verify state of a clockevent device

 include/linux/clockchips.h  | 34 ++++++++++++----------------------
 kernel/time/clockevents.c   | 31 +++++++++++++++++++++++++++++++
 kernel/time/tick-internal.h | 21 +++++++++++++++++++++
 3 files changed, 64 insertions(+), 22 deletions(-)

-- 
2.4.0

[PATCH 1/2] clockevents: Move 'enum clock_event_state' to tick-internal.h

[Viresh Kumar]

CLOCK_EVT_STATE_* symbols are local to the kernel/time and shouldn't be
exposed to other parts of the kernel.

They were added to clockchips.h as there was one external user
(arch/arm/common/bL_switcher.c).

That is modified now to not use these symbols directly:
7270d11c56f5 ("arm/bL_switcher: Kill tick suspend hackery")

We can now move them to a file local to kernel/time.

Signed-off-by: Viresh Kumar <viresh.kumar@linaro.org>
---
 include/linux/clockchips.h  | 23 +----------------------
 kernel/time/tick-internal.h | 21 +++++++++++++++++++++
 2 files changed, 22 insertions(+), 22 deletions(-)

diff --git a/include/linux/clockchips.h b/include/linux/clockchips.h
index 271fa4c8eb29..62d3007f8a8c 100644
--- a/include/linux/clockchips.h
+++ b/include/linux/clockchips.h
@@ -28,27 +28,6 @@ enum clock_event_mode {
 };
 
 /*
- * Possible states of a clock event device.
- *
- * DETACHED:	Device is not used by clockevents core. Initial state or can be
- *		reached from SHUTDOWN.
- * SHUTDOWN:	Device is powered-off. Can be reached from PERIODIC or ONESHOT.
- * PERIODIC:	Device is programmed to generate events periodically. Can be
- *		reached from DETACHED or SHUTDOWN.
- * ONESHOT:	Device is programmed to generate event only once. Can be reached
- *		from DETACHED or SHUTDOWN.
- * ONESHOT_STOPPED: Device was programmed in ONESHOT mode and is temporarily
- *		    stopped.
- */
-enum clock_event_state {
-	CLOCK_EVT_STATE_DETACHED,
-	CLOCK_EVT_STATE_SHUTDOWN,
-	CLOCK_EVT_STATE_PERIODIC,
-	CLOCK_EVT_STATE_ONESHOT,
-	CLOCK_EVT_STATE_ONESHOT_STOPPED,
-};
-
-/*
  * Clock event features
  */
 # define CLOCK_EVT_FEAT_PERIODIC	0x000001
@@ -117,7 +96,7 @@ struct clock_event_device {
 	u32			mult;
 	u32			shift;
 	enum clock_event_mode	mode;
-	enum clock_event_state	state;
+	unsigned int		state;
 	unsigned int		features;
 	unsigned long		retries;
 
diff --git a/kernel/time/tick-internal.h b/kernel/time/tick-internal.h
index 65273f0a11ed..04820f64146e 100644
--- a/kernel/time/tick-internal.h
+++ b/kernel/time/tick-internal.h
@@ -12,6 +12,27 @@
 # define TICK_DO_TIMER_NONE	-1
 # define TICK_DO_TIMER_BOOT	-2
 
+/*
+ * Possible states of a clock event device.
+ *
+ * DETACHED:	Device is not used by clockevents core. Initial state or can be
+ *		reached from SHUTDOWN.
+ * SHUTDOWN:	Device is powered-off. Can be reached from PERIODIC or ONESHOT.
+ * PERIODIC:	Device is programmed to generate events periodically. Can be
+ *		reached from DETACHED or SHUTDOWN.
+ * ONESHOT:	Device is programmed to generate event only once. Can be reached
+ *		from DETACHED or SHUTDOWN.
+ * ONESHOT_STOPPED: Device was programmed in ONESHOT mode and is temporarily
+ *		    stopped.
+ */
+enum clock_event_state {
+	CLOCK_EVT_STATE_DETACHED,
+	CLOCK_EVT_STATE_SHUTDOWN,
+	CLOCK_EVT_STATE_PERIODIC,
+	CLOCK_EVT_STATE_ONESHOT,
+	CLOCK_EVT_STATE_ONESHOT_STOPPED,
+};
+
 DECLARE_PER_CPU(struct tick_device, tick_cpu_device);
 extern ktime_t tick_next_period;
 extern ktime_t tick_period;
-- 
2.4.0

[PATCH 2/2] clockevents: Add helpers to verify state of a clockevent device

[Viresh Kumar]

Some clockevent drivers need to verify state of the clockevent device in
their callbacks or interrupt handler.

Because the symbols representing these states (defined by 'enum
clock_event_state') are internal to the core, they aren't accessible to
these driver.

Introduce helper routines that can verify state of clockevent device.

Signed-off-by: Viresh Kumar <viresh.kumar@linaro.org>
---
 include/linux/clockchips.h | 11 +++++++++++
 kernel/time/clockevents.c  | 31 +++++++++++++++++++++++++++++++
 2 files changed, 42 insertions(+)

diff --git a/include/linux/clockchips.h b/include/linux/clockchips.h
index 62d3007f8a8c..b0aa9c7b96c4 100644
--- a/include/linux/clockchips.h
+++ b/include/linux/clockchips.h
@@ -189,6 +189,12 @@ static inline void tick_setup_hrtimer_broadcast(void) { }
 
 extern int clockevents_notify(unsigned long reason, void *arg);
 
+extern bool clockevent_state_detached(struct clock_event_device *evt);
+extern bool clockevent_state_shutdown(struct clock_event_device *evt);
+extern bool clockevent_state_periodic(struct clock_event_device *evt);
+extern bool clockevent_state_oneshot(struct clock_event_device *evt);
+extern bool clockevent_state_oneshot_stopped(struct clock_event_device *evt);
+
 #else /* !CONFIG_GENERIC_CLOCKEVENTS: */
 
 static inline void clockevents_suspend(void) { }
@@ -197,6 +203,11 @@ static inline int clockevents_notify(unsigned long reason, void *arg) { return 0
 static inline int tick_check_broadcast_expired(void) { return 0; }
 static inline void tick_setup_hrtimer_broadcast(void) { }
 
+static inline bool clockevent_state_detached(struct clock_event_device *evt) { return false; };
+static inline bool clockevent_state_shutdown(struct clock_event_device *evt) { return false; };
+static inline bool clockevent_state_periodic(struct clock_event_device *evt) { return false; };
+static inline bool clockevent_state_oneshot(struct clock_event_device *evt) { return false; };
+static inline bool clockevent_state_oneshot_stopped(struct clock_event_device *evt) { return false; };
 #endif /* !CONFIG_GENERIC_CLOCKEVENTS */
 
 #endif /* _LINUX_CLOCKCHIPS_H */
diff --git a/kernel/time/clockevents.c b/kernel/time/clockevents.c
index 4922f1b805ea..ce9bb174d9bb 100644
--- a/kernel/time/clockevents.c
+++ b/kernel/time/clockevents.c
@@ -33,6 +33,37 @@ struct ce_unbind {
 	int res;
 };
 
+/* Helpers to verify state of a clockevent device */
+bool clockevent_state_detached(struct clock_event_device *evt)
+{
+	return evt->state == CLOCK_EVT_STATE_DETACHED;
+}
+EXPORT_SYMBOL_GPL(clockevent_state_detached);
+
+bool clockevent_state_shutdown(struct clock_event_device *evt)
+{
+	return evt->state == CLOCK_EVT_STATE_SHUTDOWN;
+}
+EXPORT_SYMBOL_GPL(clockevent_state_shutdown);
+
+bool clockevent_state_periodic(struct clock_event_device *evt)
+{
+	return evt->state == CLOCK_EVT_STATE_PERIODIC;
+}
+EXPORT_SYMBOL_GPL(clockevent_state_periodic);
+
+bool clockevent_state_oneshot(struct clock_event_device *evt)
+{
+	return evt->state == CLOCK_EVT_STATE_ONESHOT;
+}
+EXPORT_SYMBOL_GPL(clockevent_state_oneshot);
+
+bool clockevent_state_oneshot_stopped(struct clock_event_device *evt)
+{
+	return evt->state == CLOCK_EVT_STATE_ONESHOT_STOPPED;
+}
+EXPORT_SYMBOL_GPL(clockevent_state_oneshot_stopped);
+
 static u64 cev_delta2ns(unsigned long latch, struct clock_event_device *evt,
 			bool ismax)
 {
-- 
2.4.0

Re: [PATCH 0/2] clockevents: Hide CLOCK_EVT_STATE_* from rest of the kernel

[Thomas Gleixner]

On Wed, 20 May 2015, Viresh Kumar wrote:
> Ingo suggested [1] to keep CLOCK_EVT_STATE_* symbols somewhere in
> kernel/time/. We couldn't do it as bL_switcher code was using it
> earlier. But that's fixed now. And so the first patch moves these
> symbols to tick-internal.h.
> 
> Some of the drivers [2] need to verify state of the clockevent device
> from their callbacks or interrupt handlers.

They look at clock_event_mode and not at state, right?
 
> Because these symbols (defined by 'enum clock_event_state') will now be
> internal to the core, we need some helpers to verify state of a
> clockevent device.

So how are they affected by moving clock_event_state to the core code ?
 
> One way out was to maintain the state in drivers as well, but that would
> be unnecessary burden on them. And so the second patch introduces
> helpers for these states.

And that way we add the overhead of a full function call to those
drivers for the interrupt hot path?

I just looked at the drivers and there are three classes of mode
checks and CLOCK_EVT_MODE_ usage:

1) Interrupt handler:

   Act depending on the mode:

          - disable the device in case of oneshot

	    vf_pit_timer
	    timer-atlas7
	    sh_cmt
	    sh_tmu
	    rockchip_timer
	    qcom-timer
	    fsl_ftm_timer
	    cs5535-clockevt
	    arm_global_timer
	    evt-sb1250
	    cevt-bcm1480
	    mips/jz4740
	    dc21285-timer
	    arc/time
	    alpha/time

       	  - conditionally handle the device in case of shared
            interrupt hardware with trainwreck design or other
            shortcomings of the timer hardware

	    timer-atmel-pit
	    cs5535-clockevt
	    x86/apic

2) Sensible checks:

   i8253			init_pit_timer()
   x86/i8253			init_pit_clocksource()
   cs5535_mfgpt			init_mfgpt_timer()
   avr32/time			comparator_mode()

3) Use cases which can be fixed by conversion to the seperate mode
   setters

   x86/apic			Calibration code

4) Simple to fix stuff

   nios2			nios2_timer_config()
   exynos_mct			exynos4_mct_comp0_start()
   tcb_clksrc			tc_mode()

5) Set mode from driver code:

   time-armada-370-xp		armada_370_xp_timer_stop()
   qcom-timer			msm_local_timer_stop()
   exynos_mct			exynos4_local_timer_stop()
   arm_global_timer		gt_clockevents_stop()
   arm_arch_timer		arch_timer_stop()
   smp_twd			twd_timer_stop()
   hyperv/hv			hv_synic_cleanup()

6) Random nonsense:

   xen/time			xen_timerop_set_next_event()
   				xen_vcpuop_set_next_event()
   hyper/hv			hv_ce_set_next_event()
   sh_cmt			sh_cmt_clock_event_next()
   sh_tmu			sh_tmu_clock_event_next()
   arm/mach-imx/time		mxc_set_mode()
   arm/mach-imx/apit		epit_set_mode()
   mxs_timer			mxs_set_mode()
						
That list is way more useful than a pastebin with random grep output,
which does not cover use cases which SET a mode from driver code and
does not cover local storage of modes.

Of course you should have done that analysis before posting some
random helper functions.

Lets look how useful these functions are for the various use cases

#1) Adds function call over head to the timer interrupt

    Hot path does matter and that function call is a regression. So
    that's a NONO

#2) The function call overhead does not matter much for these, but
    they could be simply fixed by using local or device storage as
    well.

#3) A non issue

#4) Trivial to fix

#5) Trivial to replace by the explicit setter functions, but we want
    to know WHY this is done in the first place

#6) Simple to remove random crappola.

    I already did the patches while analysing the code, so that will
    be gone soon.

Now explain me how your magic functions help. For most of the cases
they would be a performance regression. And for the rest they really
do not matter at all.

Brilliant stuff that.

Thanks,

	tglx

Re: [PATCH 0/2] clockevents: Hide CLOCK_EVT_STATE_* from rest of the kernel

[Viresh Kumar]

On 20-05-15, 15:09, Thomas Gleixner wrote:
> On Wed, 20 May 2015, Viresh Kumar wrote:

> They look at clock_event_mode and not at state, right?

Yeah, it was all useful (that's what I thought initially, but not
anymore) only when we migrate some drivers to the new per-state APIs.

> And that way we add the overhead of a full function call to those
> drivers for the interrupt hot path?

Honestly, I didn't realize that this can be a blocker. My bad.

> Of course you should have done that analysis before posting some
> random helper functions.

I did looked at all the drivers few days back, but failed to give a
summary similar to yours. No excuses.

> Lets look how useful these functions are for the various use cases
> 
> #1) Adds function call over head to the timer interrupt
> 
>     Hot path does matter and that function call is a regression. So
>     that's a NONO

> Now explain me how your magic functions help. For most of the cases
> they would be a performance regression. And for the rest they really
> do not matter at all.

They wouldn't help at all in that case.

So, probably we are left with following choices:

- Maintain state internally within the driver. SMP cases need per-cpu
  storage as clkevt devices are per-cpu. Probably that's a NONO as
  well ?

- Use CLK_EVT_STATE_* directly in drivers (similar to the way we use
  CLK_EVT_MODE_* today).

- Write the routines I proposed as macros or inline functions in
  clockchips.h, and use them. Of course that wouldn't stop exposing
  CLK_EVT_STATE_* to rest of the kernel.

- Something else ?

Which one do you suggest ?

-- 
viresh

Re: [PATCH 0/2] clockevents: Hide CLOCK_EVT_STATE_* from rest of the kernel

[Thomas Gleixner]

On Wed, 20 May 2015, Viresh Kumar wrote:
> So, probably we are left with following choices:
> 
> - Maintain state internally within the driver. SMP cases need per-cpu
>   storage as clkevt devices are per-cpu. Probably that's a NONO as
>   well ?
> 
> - Use CLK_EVT_STATE_* directly in drivers (similar to the way we use
>   CLK_EVT_MODE_* today).
> 
> - Write the routines I proposed as macros or inline functions in
>   clockchips.h, and use them. Of course that wouldn't stop exposing
>   CLK_EVT_STATE_* to rest of the kernel.

I don't think that there is anything wrong with letting drivers access
it. We can make it a little bit harder to do it without accessor
functions, like I did with the state in irq_data: state_use_accessors
and have inline helpers to access it.

That makes it simple to grep for abusers :)

Thanks,

	tglx