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SubjectRe: [RFC PATCH v1 2/3] Make calls to account_scaled_stats
Vaidyanathan Srinivasan wrote:
> Hook various accounting functions to call scaled stats
>
> * Hook porcess contect switch: __switch_to()
> * Hook IRQ handling account_system_vtime() in hardirq.hA
> * Update __delayacct_add_tsk() to take care of scaling by 1000
> * Update bacct_add_tsk() to take care of scaling by 1000
>
> Signed-off-by: Amit K. Arora <aarora@linux.vnet.ibm.com>
> Signed-off-by: Vaidyanathan Srinivasan <svaidy@linux.vnet.ibm.com>
> ---
>
> arch/x86/kernel/process_32.c | 8 ++++++++
> include/linux/hardirq.h | 4 ++++
> kernel/delayacct.c | 7 ++++++-
> kernel/timer.c | 2 --
> kernel/tsacct.c | 10 ++++++++--
> 5 files changed, 26 insertions(+), 5 deletions(-)
>
> diff --git a/arch/x86/kernel/process_32.c b/arch/x86/kernel/process_32.c
> index f8476df..c81a783 100644
> --- a/arch/x86/kernel/process_32.c
> +++ b/arch/x86/kernel/process_32.c
> @@ -56,6 +56,9 @@
> #include <asm/cpu.h>
> #include <asm/kdebug.h>
>
> +extern void account_scaled_stats(struct task_struct *tsk);
> +extern void reset_for_scaled_stats(struct task_struct *tsk);
> +
> asmlinkage void ret_from_fork(void) __asm__("ret_from_fork");
>
> static int hlt_counter;
> @@ -660,6 +663,11 @@ struct task_struct * __switch_to(struct task_struct *prev_p, struct task_struct
> loadsegment(gs, next->gs);
>
> x86_write_percpu(current_task, next_p);
> + /* Account scaled statistics for the task leaving CPU */
> + account_scaled_stats(prev_p);
> + barrier();
> + /* Initialise stats counter for new task */
> + reset_for_scaled_stats(next_p);
>

This is a bad place to hook into. Can't we do scaled accounting they way we do
it for powerpc (SPURR)? I would rather hook into account_*time

> return prev_p;
> }
> diff --git a/include/linux/hardirq.h b/include/linux/hardirq.h
> index 181006c..4458736 100644
> --- a/include/linux/hardirq.h
> +++ b/include/linux/hardirq.h
> @@ -7,6 +7,9 @@
> #include <asm/hardirq.h>
> #include <asm/system.h>
>
> +/* TBD: Add config option */
> +extern void account_scaled_stats(struct task_struct *tsk);
> +
> /*
> * We put the hardirq and softirq counter into the preemption
> * counter. The bitmask has the following meaning:
> @@ -115,6 +118,7 @@ struct task_struct;
> #ifndef CONFIG_VIRT_CPU_ACCOUNTING
> static inline void account_system_vtime(struct task_struct *tsk)
> {
> + account_scaled_stats(tsk);
> }
> #endif
>
> diff --git a/kernel/delayacct.c b/kernel/delayacct.c
> index 10e43fd..3e2938f 100644
> --- a/kernel/delayacct.c
> +++ b/kernel/delayacct.c
> @@ -117,7 +117,12 @@ int __delayacct_add_tsk(struct taskstats *d, struct task_struct *tsk)
>
> tmp = (s64)d->cpu_scaled_run_real_total;
> cputime_to_timespec(tsk->utimescaled + tsk->stimescaled, &ts);
> - tmp += timespec_to_ns(&ts);
> + /* HACK: Remember, we multipled the cputime_t by 1000 to include
> + * fraction. Now it is time to scale it back to correct 'ns' value.
> + * Perhaps, we should use nano second unit (u64 type) for utimescaled
> + * and stimescaled?
> + */
> + tmp += div_s64(timespec_to_ns(&ts),1000);

1000 is a bit magical, please use a meaningful #define

> d->cpu_scaled_run_real_total =
> (tmp < (s64)d->cpu_scaled_run_real_total) ? 0 : tmp;
>
> diff --git a/kernel/timer.c b/kernel/timer.c
> index ceacc66..de8a615 100644
> --- a/kernel/timer.c
> +++ b/kernel/timer.c
> @@ -964,10 +964,8 @@ void account_process_tick(struct task_struct *p, int user_tick)
>
> if (user_tick) {
> account_user_time(p, one_jiffy);
> - account_user_time_scaled(p, cputime_to_scaled(one_jiffy));
> } else {
> account_system_time(p, HARDIRQ_OFFSET, one_jiffy);
> - account_system_time_scaled(p, cputime_to_scaled(one_jiffy));
> }

Why couldn't we leverage these functions here?

> }
> #endif
> diff --git a/kernel/tsacct.c b/kernel/tsacct.c
> index 4ab1b58..ee0d93b 100644
> --- a/kernel/tsacct.c
> +++ b/kernel/tsacct.c
> @@ -62,10 +62,16 @@ void bacct_add_tsk(struct taskstats *stats, struct task_struct *tsk)
> rcu_read_unlock();
> stats->ac_utime = cputime_to_msecs(tsk->utime) * USEC_PER_MSEC;
> stats->ac_stime = cputime_to_msecs(tsk->stime) * USEC_PER_MSEC;
> + /* HACK: cputime unit is jiffies on x86 and not good for fractional
> + * additional. cputime_t type {u,s}timescaled is multiplied by
> + * 1000 for scaled accounting. Hence, cputime_to_msecs will actually
> + * give the required micro second value. The multiplier
> + * USEC_PER_MSEC has been dropped.
> + */
> stats->ac_utimescaled =
> - cputime_to_msecs(tsk->utimescaled) * USEC_PER_MSEC;
> + cputime_to_msecs(tsk->utimescaled);
> stats->ac_stimescaled =
> - cputime_to_msecs(tsk->stimescaled) * USEC_PER_MSEC;
> + cputime_to_msecs(tsk->stimescaled);
> stats->ac_minflt = tsk->min_flt;
> stats->ac_majflt = tsk->maj_flt;
>
>


--
Warm Regards,
Balbir Singh
Linux Technology Center
IBM, ISTL


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