Re: [PATCH] Use boot based time for process start time and boot time in /proc

[Andrew Morton <akpm@linux-foundation.org>]

On Thu, 10 May 2007 19:10:42 +0200
Tomas Janousek <tjanouse@redhat.com> wrote:

> Commit 411187fb05cd11676b0979d9fbf3291db69dbce2 caused boot time to move and
> process start times to become invalid after suspend. Using boot based time for
> those restores the old behaviour and fixes the issue.
> 
> ..
>
> @@ -445,12 +445,14 @@ static int show_stat(struct seq_file *p, void *v)
>  	unsigned long jif;
>  	cputime64_t user, nice, system, idle, iowait, irq, softirq, steal;
>  	u64 sum = 0;
> +	struct timespec boottime;
>  
>  	user = nice = system = idle = iowait =
>  		irq = softirq = steal = cputime64_zero;
> -	jif = - wall_to_monotonic.tv_sec;
> -	if (wall_to_monotonic.tv_nsec)
> -		--jif;
> +	getboottime(&boottime);
> +	jif = boottime.tv_sec;
> +	if (boottime.tv_nsec)
> +		++jif;
>

Is the switch from --jif to ++jif a functional change?  If so, how come?

>  	for_each_possible_cpu(i) {
>  		int j;
> diff --git a/include/linux/sched.h b/include/linux/sched.h
> index 40645b4..386ff51 100644
> --- a/include/linux/sched.h
> +++ b/include/linux/sched.h
> @@ -918,7 +918,7 @@ struct task_struct {
>  	unsigned int rt_priority;
>  	cputime_t utime, stime;
>  	unsigned long nvcsw, nivcsw; /* context switch counts */
> -	struct timespec start_time;
> +	struct timespec start_time, real_start_time;

no, please prefer to do

	struct timespec start_time;
	struct timespec real_start_time;

which gives a nice place to add a comment documenting the field.

Please document fields.

What is the difference between start_time and real_start_time?