Messages in this thread | | | Date | Mon, 07 Aug 2006 14:23:00 -0700 | From | Jay Lan <> | Subject | Re: [patch 1/3] add basic accounting fields to taskstats |
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Jay Lan wrote:
[snip]
>> >> >>> + /* Each process gets a minimum of a half tick cpu time */ >>> + if ((stats->ac_utime == 0) && (stats->ac_stime == 0)) { >>> + stats->ac_stime = USEC_PER_TICK/2; >>> + } >>> + >> >> >> >> This is confusing. Half tick does not make any sense from the >> scheduler view point (or am I missing something?), so why >> return half a tick to the user. > > > It must be inherited from old code dated back to Cray UNICOS. > I do not know if bad thing can happen if both utime and stime > are less than 1 usec... I guess not. But i agree that > half a tick does not make sense. To play safe, we can change > it to 1 usec if both utime and stime are sub microsecond. > What do you think?
Hi Balbir,
I figured this out. The tsk->stime (and utime as well) are charged by 1 tick (or cputime) from the timer interrupt handler through update_process_times->account_{user,system}_time.
The clock resolution is a tick. Any short process less than 1 tick will the counter being 0. It can be from 0 to 0.99999... tick. A half tick is the average value.
I think it makes more sense to assign a half tick than assign 1 usec to the stime. What do you think? Certainly the code need better explanation.
Regards, - jay
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