Re: /proc or ps tools bug? 2.6.3, time is off

[George Anzinger <george@mvista.com>]

John,

This is the other place I found "start_time" being used.  It is at about line 
340 in kernel/acct.c.  The same sort of math should be done here:

	elapsed = get_jiffies_64() - current->start_time;
	ac.ac_etime = encode_comp_t(elapsed < (unsigned long) -1l ?
	                       (unsigned long) elapsed : (unsigned long) -1l);
	do_div(elapsed, HZ);

-g

john stultz wrote:
> On Wed, 2004-02-25 at 13:10, George Anzinger wrote:
> 
>>Albert Cahalan wrote:
>>
>>>This is NOT sane. Remeber that procps doesn't get to see HZ.
>>>Only USER_HZ is available, as the AT_CLKTCK ELF note.
>>>
>>>I think the way to fix this is to skip or add a tick
>>>every now and then, so that the long-term HZ is exact.
>>>
>>>Another way is to simply choose between pure old-style
>>>tick-based timekeeping and pure new-style cycle-based
>>>(TSC or ACPI) timekeeping. Systems with uncooperative
>>>hardware have to use the old-style time keeping. This
>>>should simply the code greatly.
>>
>>On checking the code and thinking about this, I would suggest that we change 
>>start_time in the task struct to be the wall time (or monotonic time if that 
>>seems better).  I only find two places this is used, in proc and in the 
>>accounting code.  Both of these could easily be changed.  Of course, even 
>>leaving it as it is, they could be changed to report more correct values by 
>>using the correct conversions to translate the system HZ to USER_HZ.
> 
> 
> Is this close to what your thinking of? 
> I can't reproduce the issue on my systems, so I'll need someone else to
> test this. 
> 
> thanks
> -john
> 
> --- 1.5/include/linux/times.h	Sun Nov  9 19:26:08 2003
> +++ edited/include/linux/times.h	Wed Feb 25 17:39:11 2004
> @@ -7,7 +7,7 @@
>  #include <asm/param.h>
>  
>  #if (HZ % USER_HZ)==0
> -# define jiffies_to_clock_t(x) ((x) / (HZ / USER_HZ))
> +# define jiffies_to_clock_t(x) (((x*TICK_NSEC*HZ)/NSEC_PER_SEC) / (HZ / USER_HZ))
>  #else
>  # define jiffies_to_clock_t(x) ((clock_t) jiffies_64_to_clock_t((u64) x))
>  #endif
> 
> 
> 
> 
> -
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-- 
George Anzinger   george@mvista.com
High-res-timers:  http://sourceforge.net/projects/high-res-timers/
Preemption patch: http://www.kernel.org/pub/linux/kernel/people/rml