Re: [PATCH] Re: boot time, process start time, and NOW time

[Albert Cahalan <albert@users.sf.net>]

On Tue, 2004-08-17 at 21:09, john stultz wrote:
> On Tue, 2004-08-17 at 15:19, Albert Cahalan wrote:
> > On Tue, 2004-08-17 at 20:11, john stultz wrote:
> > 
> > > --- 1.62/fs/proc/array.c	2004-08-05 13:36:53 -07:00
> > > +++ edited/fs/proc/array.c	2004-08-17 17:08:07 -07:00
> > > @@ -356,7 +356,14 @@
> > >  	read_unlock(&tasklist_lock);
> > >  
> > >  	/* Temporary variable needed for gcc-2.96 */
> > > -	start_time = jiffies_64_to_clock_t(task->start_time - INITIAL_JIFFIES);
> > > +	/* convert timespec -> nsec*/
> > > +	start_time = (unsigned long long)task->start_time.tv_sec * NSEC_PER_SEC 
> > > +				+ task->start_time.tv_nsec;
> > > +	/* convert nsec -> ticks */
> > > +	start_time *= HZ;
> > > +	do_div(start_time, NSEC_PER_SEC);
> > > +	/* convert ticks -> USER_HZ ticks */
> > > +	start_time = jiffies_64_to_clock_t(start_time);
> > 
> > This would overflow in about 6 months at 1024 USER_HZ.
> > Various possible alternatives:
> 
> Everybody sing: Thanks, nice catch/Here's an updated patch!
> 
> -john
> 
> ===== fs/proc/array.c 1.62 vs edited =====
> --- 1.62/fs/proc/array.c	2004-08-05 13:36:53 -07:00
> +++ edited/fs/proc/array.c	2004-08-17 18:03:55 -07:00
> @@ -356,7 +356,13 @@
>  	read_unlock(&tasklist_lock);
>  
>  	/* Temporary variable needed for gcc-2.96 */
> -	start_time = jiffies_64_to_clock_t(task->start_time - INITIAL_JIFFIES);
> +	/* convert timespec -> nsec*/
> +	start_time = (unsigned long long)task->start_time.tv_sec * NSEC_PER_SEC 
> +				+ task->start_time.tv_nsec;
> +	/* convert nsec -> ticks */
> +	do_div(start_time, NSEC_PER_SEC/HZ);
> +	/* convert ticks -> USER_HZ ticks */
> +	start_time = jiffies_64_to_clock_t(start_time);

NSEC_PER_SEC/HZ isn't an integer when HZ is 1024.
Also, you're doing two conversions. You can go directly
from nanoseconds to USER_HZ, without using HZ at all.

I think you really need the #if for this.
It could go in a header if you like, creating
a timespec_to_clock_t macro for use in proc.