Subject: Re: [PATCH 1/2] Add scaled time to taskstats based process accounting

From: Andrew Morton <[email-masked]>
Date: Fri, 17 Aug 2007 11:59:51 -0700

On Fri, 17 Aug 2007 11:09:41 +1000
Michael Neuling <[email-masked]> wrote:

> This adds items to the taststats struct to account for user and system
> time based on scaling the CPU frequency and instruction issue rates.
> 
> Adds account_(user|system)_time_scaled callbacks which architectures
> can use to account for time using this mechanism.
> 
> ...
> 
> Index: linux-2.6-ozlabs/include/linux/kernel_stat.h
> ===================================================================
> --- linux-2.6-ozlabs.orig/include/linux/kernel_stat.h
> +++ linux-2.6-ozlabs/include/linux/kernel_stat.h
> @@ -52,7 +52,9 @@ static inline int kstat_irqs(int irq)
>  }
>  
>  extern void account_user_time(struct task_struct *, cputime_t);
> +extern void account_user_time_scaled(struct task_struct *, cputime_t);
>  extern void account_system_time(struct task_struct *, int, cputime_t);
> +extern void account_system_time_scaled(struct task_struct *, cputime_t);
>  extern void account_steal_time(struct task_struct *, cputime_t);
>  
>  #endif /* _LINUX_KERNEL_STAT_H */
> Index: linux-2.6-ozlabs/include/linux/sched.h
> ===================================================================
> --- linux-2.6-ozlabs.orig/include/linux/sched.h
> +++ linux-2.6-ozlabs/include/linux/sched.h
> @@ -1020,7 +1020,7 @@ struct task_struct {
>  	int __user *clear_child_tid;		/* CLONE_CHILD_CLEARTID */
>  
>  	unsigned int rt_priority;
> -	cputime_t utime, stime;
> +	cputime_t utime, stime, utimescaled, stimescaled;

Adding 8 or 16 bytes to the task_struct for all architectures for something
which only powerpc uses?

Is there any prospect that other CPUs can use this?

>  	unsigned long nvcsw, nivcsw; /* context switch counts */
>  	struct timespec start_time; 		/* monotonic time */
>  	struct timespec real_start_time;	/* boot based time */
> Index: linux-2.6-ozlabs/include/linux/taskstats.h
> ===================================================================
> --- linux-2.6-ozlabs.orig/include/linux/taskstats.h
> +++ linux-2.6-ozlabs/include/linux/taskstats.h
> @@ -31,7 +31,7 @@
>   */
>  
>  
> -#define TASKSTATS_VERSION	5
> +#define TASKSTATS_VERSION	6
>  #define TS_COMM_LEN		32	/* should be >= TASK_COMM_LEN
>  					 * in linux/sched.h */
>  
> @@ -85,9 +85,12 @@ struct taskstats {
>  	 * On some architectures, value will adjust for cpu time stolen
>  	 * from the kernel in involuntary waits due to virtualization.
>  	 * Value is cumulative, in nanoseconds, without a corresponding count
> -	 * and wraps around to zero silently on overflow
> +	 * and wraps around to zero silently on overflow.  The
> +	 * _scaled_ version accounts for cpus which can scale the
> +	 * number of instructions executed each cycle.
>  	 */
>  	__u64	cpu_run_real_total;
> +	__u64	cpu_scaled_run_real_total;
>  
>  	/* cpu "virtual" running time
>  	 * Uses time intervals seen by the kernel i.e. no adjustment
> @@ -142,6 +145,10 @@ struct taskstats {
>  	__u64	write_char;		/* bytes written */
>  	__u64	read_syscalls;		/* read syscalls */
>  	__u64	write_syscalls;		/* write syscalls */
> +
> +	/* time accounting for SMT machines */
> +	__u64	ac_utimescaled;		/* utime scaled on frequency etc */
> +	__u64	ac_stimescaled;		/* stime scaled on frequency etc */
>  	/* Extended accounting fields end */

umm, should we be adding new fields in the middle of this message?  I
thought we should only add to the end, for back-compatibility, but maybe I
misremember.