linux-kernel - Re: [patch 1/3] add basic accounting fields to taskstats

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Message-ID: <44D8BE71.4010807@engr.sgi.com>
Date:	Tue, 08 Aug 2006 09:40:17 -0700
From:	Jay Lan <jlan@...r.sgi.com>
To:	balbir@...ibm.com
CC:	Andrew Morton <akpm@...l.org>, lkml <linux-kernel@...r.kernel.org>,
	Shailabh Nagar <nagar@...son.ibm.com>,
	Jes Sorensen <jes@....com>,
	Chris Sturtivant <csturtiv@....com>, Tony Ernst <tee@....com>
Subject: Re: [patch 1/3] add basic accounting fields to taskstats

Balbir Singh wrote:
> Jay Lan wrote:
>> 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.
>>
>
> But the scheduling happens in the granularity of a tick, so the
> minimum each task gets is a tick.
>
>> 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.
>>
>
> Can't we leave these values as zero in case both stime and utime are
> zero.

Yes, i will leave them as zero in this case.

Regards,
 - jay

>
>
>> Regards,
>>  - jay
>>
>>
>> [snip]
>
>

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