linux-kernel - Re: [RFC PATCH v1 2/3] Make calls to account_scaled

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Date:	Mon, 26 May 2008 23:48:04 +0530
From:	Balbir Singh <balbir@...ux.vnet.ibm.com>
To:	Vaidyanathan Srinivasan <svaidy@...ux.vnet.ibm.com>
CC:	Linux Kernel <linux-kernel@...r.kernel.org>,
	venkatesh.pallipadi@...el.com, suresh.b.siddha@...el.com,
	Michael Neuling <mikey@...ling.org>,
	"Amit K. Arora" <aarora@...ux.vnet.ibm.com>
Subject: Re: [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@...ux.vnet.ibm.com>
> Signed-off-by: Vaidyanathan Srinivasan <svaidy@...ux.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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