[PATCH v2] Fix hardware IRQ time accounting problem.

[Tony Breeds]

The commit fa13a5a1f25f671d084d8884be96fc48d9b68275 (sched: restore
deterministic CPU accounting on powerpc), unconditionally calls
update_process_tick() in system context. In the deterministic accounting case
this is the correct thing to do. However, in the non-deterministic accounting
case we need to not do this, and results in the time accounted as hardware irq
time being artificially elevated.

Also this patch collapses 2 consecutive '#ifdef CONFIG_VIRT_CPU_ACCOUNTING'
checks in time.h into one for neatness.

Signed-off-by: Tony Breeds <***@bakeyournoodle.com>
---
The problem was seen and reported by Johannes Berg and Frederik Himpe.
Paul, I think this is good for 2.6.24.

Changes since v1:
- I noticed that the #define was explictly using "current" rather than
the task passed in. Using tsk is the right thing to do.
- The whiteapce changes dirty-up the patch and are un-needed with the
change above.

arch/powerpc/kernel/process.c | 2 +-
include/asm-powerpc/time.h | 8 ++------
2 files changed, 3 insertions(+), 7 deletions(-)

diff --git a/arch/powerpc/kernel/process.c b/arch/powerpc/kernel/process.c
index 41e13f4..b9d8837 100644
--- a/arch/powerpc/kernel/process.c
+++ b/arch/powerpc/kernel/process.c
@@ -350,7 +350,7 @@ struct task_struct *__switch_to(struct task_struct *prev,
local_irq_save(flags);

account_system_vtime(current);
- account_process_tick(current, 0);
+ account_process_vtime(current);
calculate_steal_time();

last = _switch(old_thread, new_thread);
diff --git a/include/asm-powerpc/time.h b/include/asm-powerpc/time.h
index 780f826..a7281e0 100644
--- a/include/asm-powerpc/time.h
+++ b/include/asm-powerpc/time.h
@@ -237,18 +237,14 @@ struct cpu_usage {

DECLARE_PER_CPU(struct cpu_usage, cpu_usage_array);

-#ifdef CONFIG_VIRT_CPU_ACCOUNTING
-extern void account_process_vtime(struct task_struct *tsk);
-#else
-#define account_process_vtime(tsk) do { } while (0)
-#endif

[Johannes Berg]

Post by Tony Breeds
The commit fa13a5a1f25f671d084d8884be96fc48d9b68275 (sched: restore
deterministic CPU accounting on powerpc), unconditionally calls
update_process_tick() in system context. In the deterministic accounting case
this is the correct thing to do. However, in the non-deterministic accounting
case we need to not do this, and results in the time accounted as hardware irq
time being artificially elevated.

Cool, I wouldn't have stood a chance of tracking this down :) Thanks,
I'll apply it to my testing tree later today.

Post by Tony Breeds
---
The problem was seen and reported by Johannes Berg and Frederik Himpe.
Paul, I think this is good for 2.6.24.
- I noticed that the #define was explictly using "current" rather than
the task passed in. Using tsk is the right thing to do.
- The whiteapce changes dirty-up the patch and are un-needed with the
change above.
arch/powerpc/kernel/process.c | 2 +-
include/asm-powerpc/time.h | 8 ++------
2 files changed, 3 insertions(+), 7 deletions(-)
diff --git a/arch/powerpc/kernel/process.c b/arch/powerpc/kernel/process.c
index 41e13f4..b9d8837 100644
--- a/arch/powerpc/kernel/process.c
+++ b/arch/powerpc/kernel/process.c
@@ -350,7 +350,7 @@ struct task_struct *__switch_to(struct task_struct *prev,
local_irq_save(flags);
account_system_vtime(current);
- account_process_tick(current, 0);
+ account_process_vtime(current);
calculate_steal_time();
last = _switch(old_thread, new_thread);
diff --git a/include/asm-powerpc/time.h b/include/asm-powerpc/time.h
index 780f826..a7281e0 100644
--- a/include/asm-powerpc/time.h
+++ b/include/asm-powerpc/time.h
@@ -237,18 +237,14 @@ struct cpu_usage {
DECLARE_PER_CPU(struct cpu_usage, cpu_usage_array);
-#ifdef CONFIG_VIRT_CPU_ACCOUNTING
-extern void account_process_vtime(struct task_struct *tsk);
-#else
-#define account_process_vtime(tsk) do { } while (0)
-#endif
-
#if defined(CONFIG_VIRT_CPU_ACCOUNTING)
extern void calculate_steal_time(void);
extern void snapshot_timebases(void);
+#define account_process_vtime(tsk) account_process_tick(tsk, 0);
#else
#define calculate_steal_time() do { } while (0)
#define snapshot_timebases() do { } while (0)
+#define account_process_vtime(tsk) do { } while (0)
#endif
extern void secondary_cpu_time_init(void);

[Frederik Himpe]

Post by Tony Breeds
The commit fa13a5a1f25f671d084d8884be96fc48d9b68275 (sched: restore
deterministic CPU accounting on powerpc), unconditionally calls
update_process_tick() in system context. In the deterministic
accounting case this is the correct thing to do. However, in the
non-deterministic accounting case we need to not do this, and results in
the time accounted as hardware irq time being artificially elevated.
Also this patch collapses 2 consecutive '#ifdef
CONFIG_VIRT_CPU_ACCOUNTING' checks in time.h into one for neatness.

I can confirm this patch fixed the problem for me. Thank you!