powerpc: re-enable dynticks

PATCH Superseded Paul Clarke 5 participants 10 messages Feb 13, 2015 – Feb 27, 2015 PowerPC

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Paul E. McKenney

Acked-by on v1 1/1

2015-02-13 20:42 UTC #1 lore raw

Quoted 16 lines · Paul Clarke

implement arch_irq_work_has_interrupt() for powerpc
Commit 9b01f5bf3 introduced a dependency on "IRQ work self-IPIs" for full dynamic ticks to be enabled, by expecting architectures to implement a suitable arch_irq_work_has_interrupt() routine.
Several arches have implemented this routine, including x86 (3010279f) and arm (09f6edd4), but powerpc was omitted.
This patch implements this routine for powerpc.
The symptom, at boot (on powerpc arch systems) with "nohz_full=<CPU list>" is displayed:
NO_HZ: Can't run full dynticks because arch doesn't support irq
work self-IPIs

Quoted 8 lines

after this patch:
NO_HZ: Full dynticks CPUs: <CPU list>.
Tested against 3.19.
CC Frederic Weisbecker <[email protected]>
CC Paul E. McKenney <[email protected]>
Signed-off-by Paul A. Clarke <[email protected]>

Acked-by Paul E. McKenney <[email protected]>

Quoted 28 lines

arch/powerpc/include/asm/irq_work.h new file +11 -1
new file mode 100644
index 0000000..18365ec
@@ -0,0 +1,11 @@
+#ifndef _ASM_IRQ_WORK_H
+#define _ASM_IRQ_WORK_H
+
+#include <asm/processor.h>
+
+static inline bool arch_irq_work_has_interrupt(void)
+{
+	return 1;
+}
+
+#endif /* _ASM_IRQ_WORK_H */
 
--
Regards,
Paul Clarke, IBM
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Michael Ellerman

reviewer

2015-02-16 00:08 UTC #2 lore raw

In reply to Paul Clarke

Quoted 16 lines · Paul Clarke

implement arch_irq_work_has_interrupt() for powerpc
Commit 9b01f5bf3 introduced a dependency on "IRQ work self-IPIs" for full dynamic ticks to be enabled, by expecting architectures to implement a suitable arch_irq_work_has_interrupt() routine.
Several arches have implemented this routine, including x86 (3010279f) and arm (09f6edd4), but powerpc was omitted.
This patch implements this routine for powerpc.
The symptom, at boot (on powerpc arch systems) with "nohz_full=<CPU list>" is displayed:
NO_HZ: Can't run full dynticks because arch doesn't support irq
work self-IPIs

Quoted 4 lines

after this patch:
NO_HZ: Full dynticks CPUs: <CPU list>.
Tested against 3.19.

It makes the message change, but is that correct? ie. do we actually implement "IRQ work self-IPIs"?

Quoted 7 lines

arch/powerpc/include/asm/irq_work.h new file +0 -0
new file mode 100644
index 0000000..18365ec

arch/powerpc/include/asm/irq_work.h line 8

Quoted 8 lines

arch/powerpc/include/asm/irq_work.h new file +8 -0

@@ -0,0 +1,11 @@
+#ifndef _ASM_IRQ_WORK_H
+#define _ASM_IRQ_WORK_H
+
+#include <asm/processor.h>
+
+static inline bool arch_irq_work_has_interrupt(void)
+{
+	return 1;

Should be "true";

arch/powerpc/include/asm/irq_work.h line 9

Quoted 1 line

arch/powerpc/include/asm/irq_work.h new file +1 -0
+}

cheers

Benjamin Herrenschmidt

2015-02-16 04:06 UTC #3 lore raw

Quoted 7 lines · Michael Ellerman

Quoted 6 lines · Paul Clarke
implement arch_irq_work_has_interrupt() for powerpc
Commit 9b01f5bf3 introduced a dependency on "IRQ work self-IPIs" for full dynamic ticks to be enabled, by expecting architectures to implement a suitable arch_irq_work_has_interrupt() routine.

Quoted 5 lines

Quoted 5 lines
Several arches have implemented this routine, including x86 (3010279f) and arm (09f6edd4), but powerpc was omitted.
This patch implements this routine for powerpc.

.../...

Quoted 3 lines

It makes the message change, but is that correct? ie. do we actually implement "IRQ work self-IPIs"?

I think so... Fred, do you think what we do will work ? We hijack our decrementer (local timer) by making it shoot almost immediately (1 tick away) and run the irq work at the beginning of __timer_interrupt().

At that point we are on our irq stack and have done irq_enter but that's about it.

Cheers,
Ben.

Quoted 27 lines

Quoted 7 lines
arch/powerpc/include/asm/irq_work.h new file +0 -0
new file mode 100644
index 0000000..18365ec
arch/powerpc/include/asm/irq_work.h line 8
Quoted 8 lines
arch/powerpc/include/asm/irq_work.h new file +8 -0
@@ -0,0 +1,11 @@
+#ifndef _ASM_IRQ_WORK_H
+#define _ASM_IRQ_WORK_H
+
+#include <asm/processor.h>
+
+static inline bool arch_irq_work_has_interrupt(void)
+{
+	return 1;
Should be "true";
arch/powerpc/include/asm/irq_work.h line 9
Quoted 1 line
arch/powerpc/include/asm/irq_work.h new file +1 -0
+}
cheers
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Frederic Weisbecker

2015-02-22 22:14 UTC #4 lore raw

Hi Ben,

2015-02-16 5:06 GMT+01:00 Benjamin Herrenschmidt <[email protected]>:

Quoted 18 lines · Michael Ellerman

Quoted 7 lines · Paul Clarke
Quoted 6 lines
implement arch_irq_work_has_interrupt() for powerpc
Commit 9b01f5bf3 introduced a dependency on "IRQ work self-IPIs" for full dynamic ticks to be enabled, by expecting architectures to implement a suitable arch_irq_work_has_interrupt() routine.
Quoted 5 lines
Quoted 5 lines
Several arches have implemented this routine, including x86 (3010279f) and arm (09f6edd4), but powerpc was omitted.
This patch implements this routine for powerpc.
.../...
Quoted 3 lines
It makes the message change, but is that correct? ie. do we actually implement "IRQ work self-IPIs"?

Quoted 6 lines

I think so... Fred, do you think what we do will work ? We hijack our decrementer (local timer) by making it shoot almost immediately (1 tick away) and run the irq work at the beginning of __timer_interrupt().
At that point we are on our irq stack and have done irq_enter but that's about it.

Yes that should work. After all "self-IPI" is an oxymoron. One would expect an IPI to be triggered by an irq controller but if such operation isn't supported with the current CPU being both source and destination, anything triggering the desired callback in an interrupt context in a reasonable amount of time ahead does the job here.

I thought well that's what powerpc was doing for irq work but I wasn't sure I understood the code correctly. I should have pinged people about that, sorry.

Thanks.

Quoted 33 lines

Cheers,
Ben.
Quoted 27 lines
Quoted 7 lines
arch/powerpc/include/asm/irq_work.h new file +0 -0
new file mode 100644
index 0000000..18365ec
arch/powerpc/include/asm/irq_work.h line 8
Quoted 8 lines
arch/powerpc/include/asm/irq_work.h new file +8 -0
@@ -0,0 +1,11 @@
+#ifndef _ASM_IRQ_WORK_H
+#define _ASM_IRQ_WORK_H
+
+#include <asm/processor.h>
+
+static inline bool arch_irq_work_has_interrupt(void)
+{
+   return 1;
Should be "true";
arch/powerpc/include/asm/irq_work.h line 9
Quoted 1 line
arch/powerpc/include/asm/irq_work.h new file +1 -0
+}
cheers
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Benjamin Herrenschmidt

2015-02-22 22:30 UTC #5 lore raw

Quoted 5 lines · Frederic Weisbecker

Yes that should work. After all "self-IPI" is an oxymoron. One would expect an IPI to be triggered by an irq controller but if such operation isn't supported with the current CPU being both source and destination, anything triggering the desired callback in an interrupt context in a reasonable amount of time ahead does the job here.

We could do self-IPI on platforms that have an SMP-capable interrupt controller too but it would probably have higher overhead and would require verifying that the code for each of our different interrupt controllers is safe to be called from NMIs (hint: ioremap space isn't safe to access from NMIs for us on some CPU families...).

We might be able to do better than using the decrementer on some CPUs by using local doorbells, but for now this will do.

Quoted 3 lines

I thought well that's what powerpc was doing for irq work but I wasn't sure I understood the code correctly. I should have pinged people about that, sorry.

No worries,

Cheers,
Ben.

Paul Clarke

author

2015-02-20 17:08 UTC #6 lore raw

PATCH v2 1/1 powerpc: re-enable dynticks

In reply to Michael Ellerman

implement arch_irq_work_has_interrupt() for powerpc

Commit 9b01f5bf3 introduced a dependency on "IRQ work self-IPIs" for full dynamic ticks to be enabled, by expecting architectures to implement a suitable arch_irq_work_has_interrupt() routine.

Several arches have implemented this routine, including x86 (3010279f) and arm (09f6edd4), but powerpc was omitted.

This patch implements this routine for powerpc.

The symptom, at boot (on powerpc arch systems) with "nohz_full=<CPU list>" is displayed:
NO_HZ: Can't run full dynticks because arch doesn't support irq
work self-IPIs

after this patch:
NO_HZ: Full dynticks CPUs: <CPU list>.

Tested against 3.19.

v2: changed "return 1" to "return true", per Michael Ellerman

CC Frederic Weisbecker <[email protected]>

CC Paul E. McKenney <[email protected]>

Signed-off-by Paul A. Clarke <[email protected]>

arch/powerpc/include/asm/irq_work.h new file +11 -0

new file mode 100644
index 0000000..99cc0aa
@@ -0,0 +1,11 @@
+#ifndef _ASM_IRQ_WORK_H
+#define _ASM_IRQ_WORK_H
+
+#include <asm/processor.h>
+
+static inline bool arch_irq_work_has_interrupt(void)
+{
+	return true;
+}
+
+#endif /* _ASM_IRQ_WORK_H */

Paul Clarke

author

2015-02-20 17:13 UTC #7 lore raw

PATCH v2 1/1 powerpc: re-enable dynticks

In reply to Michael Ellerman

implement arch_irq_work_has_interrupt() for powerpc

(resending because I messed up the e-mail addresses)

Commit 9b01f5bf3 introduced a dependency on "IRQ work self-IPIs" for full dynamic ticks to be enabled, by expecting architectures to implement a suitable arch_irq_work_has_interrupt() routine.

Several arches have implemented this routine, including x86 (3010279f) and arm (09f6edd4), but powerpc was omitted.

This patch implements this routine for powerpc.

The symptom, at boot (on powerpc arch systems) with "nohz_full=<CPU list>" is displayed:
NO_HZ: Can't run full dynticks because arch doesn't support irq
work self-IPIs

after this patch:
NO_HZ: Full dynticks CPUs: <CPU list>.

Tested against 3.19.

v2: changed "return 1" to "return true", per Michael Ellerman

CC Frederic Weisbecker <[email protected]>

CC Paul E. McKenney <[email protected]>

Signed-off-by Paul A. Clarke <[email protected]>

arch/powerpc/include/asm/irq_work.h new file +11 -0

new file mode 100644
index 0000000..99cc0aa
@@ -0,0 +1,11 @@
+#ifndef _ASM_IRQ_WORK_H
+#define _ASM_IRQ_WORK_H
+
+#include <asm/processor.h>
+
+static inline bool arch_irq_work_has_interrupt(void)
+{
+    return true;
+}
+
+#endif /* _ASM_IRQ_WORK_H */

Paul E. McKenney

Reviewed-by on v2 1/1

2015-02-21 05:18 UTC #8 lore raw

Quoted 22 lines · Paul Clarke

implement arch_irq_work_has_interrupt() for powerpc
(resending because I messed up the e-mail addresses)
Commit 9b01f5bf3 introduced a dependency on "IRQ work self-IPIs" for full dynamic ticks to be enabled, by expecting architectures to implement a suitable arch_irq_work_has_interrupt() routine.
Several arches have implemented this routine, including x86 (3010279f) and arm (09f6edd4), but powerpc was omitted.
This patch implements this routine for powerpc.
The symptom, at boot (on powerpc arch systems) with "nohz_full=<CPU list>" is displayed:
NO_HZ: Can't run full dynticks because arch doesn't support irq
work self-IPIs
after this patch:
NO_HZ: Full dynticks CPUs: <CPU list>.

Quoted 7 lines

Tested against 3.19.
v2: changed "return 1" to "return true", per Michael Ellerman
CC Frederic Weisbecker <[email protected]>
CC Paul E. McKenney <[email protected]>
Signed-off-by Paul A. Clarke <[email protected]>

Reviewed-by Paul E. McKenney <[email protected]>

Quoted 18 lines

arch/powerpc/include/asm/irq_work.h new file +11 -0

new file mode 100644
index 0000000..99cc0aa
@@ -0,0 +1,11 @@
+#ifndef _ASM_IRQ_WORK_H
+#define _ASM_IRQ_WORK_H
+
+#include <asm/processor.h>
+
+static inline bool arch_irq_work_has_interrupt(void)
+{
+    return true;
+}
+
+#endif /* _ASM_IRQ_WORK_H */

Paul Clarke

author

2015-02-27 13:28 UTC #9 lore raw

It appears the discussion wrapped up on this, favorably. Is there anything else I need to do to get this merged?

Regards,
PC

Quoted 57 lines · Paul E. McKenney

Quoted 22 lines · Paul Clarke
implement arch_irq_work_has_interrupt() for powerpc
(resending because I messed up the e-mail addresses)
Commit 9b01f5bf3 introduced a dependency on "IRQ work self-IPIs" for full dynamic ticks to be enabled, by expecting architectures to implement a suitable arch_irq_work_has_interrupt() routine.
Several arches have implemented this routine, including x86 (3010279f) and arm (09f6edd4), but powerpc was omitted.
This patch implements this routine for powerpc.
The symptom, at boot (on powerpc arch systems) with "nohz_full=<CPU list>" is displayed:
NO_HZ: Can't run full dynticks because arch doesn't support irq
work self-IPIs
after this patch:
NO_HZ: Full dynticks CPUs: <CPU list>.
Quoted 7 lines
Tested against 3.19.
v2: changed "return 1" to "return true", per Michael Ellerman
CC Frederic Weisbecker <[email protected]>
CC Paul E. McKenney <[email protected]>
Signed-off-by Paul A. Clarke <[email protected]>
Reviewed-by Paul E. McKenney <[email protected]>
Quoted 8 lines
arch/powerpc/include/asm/irq_work.h new file +1 -0
new file mode 100644
index 0000000..99cc0aa
@@ -0,0 +1,11 @@
+#ifndef _ASM_IRQ_WORK_H
arch/powerpc/include/asm/irq_work.h line 11
Quoted 10 lines
arch/powerpc/include/asm/irq_work.h new file +10 -0
+#define _ASM_IRQ_WORK_H
+
+#include <asm/processor.h>
+
+static inline bool arch_irq_work_has_interrupt(void)
+{
+    return true;
+}
+
+#endif /* _ASM_IRQ_WORK_H */
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