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

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Date:	Tue, 01 Aug 2006 14:51:32 -0700
From:	Jay Lan <jlan@....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:
> 
>>  
>> -#define TASKSTATS_VERSION    1
>> +#define TASKSTATS_VERSION    2
>> +#define TASK_COMM_LEN        16
>>  
> 
> 
> We should find a way to keep this in sync with with the definition
> in linux/sched.h (won't we a warning if both this header and
> linux/sched.h are included together?)

I do not know how to sync it up. This header linux/taskstats.h is
meant to be included by userspace programs. If an application
happens to include linux/sched.h, which includes linux/time.h,
the application will very likely have compilation errors because
the "struct timespec" declaration in <linux/time.h> and <time.h>
are conflicting.

The <linux/acct.h> defines it to
#define ACCT_COMM    16

I can change our define to TS_COMM_LEN with remakes saying it
should be in sync with the TAKS_COMM_LEN defined in linux/sched.h.

If there is a better way, i am eager to know it.

> 
> 
> 
>> + * fill in basic accounting fields
>> + */
>> +static void bacct_add_tsk(struct taskstats *stats, struct task_struct 
>> *tsk)
>> +{
>> +    u64    run_time;
>> +    struct timespec uptime;
>> +
>> +    /* calculate run_time in nsec */
>> +    do_posix_clock_monotonic_gettime(&uptime);
>> +    run_time = (u64)uptime.tv_sec*NSEC_PER_SEC + uptime.tv_nsec;
>> +    run_time -= (u64)current->group_leader->start_time.tv_sec * 
>> NSEC_PER_SEC
>> +            + current->group_leader->start_time.tv_nsec;
>> +    do_div(run_time, NSEC_PER_USEC);    /* rebase run_time to usec */
>> +    stats->ac_etime = run_time;
>> +    do_div(run_time, USEC_PER_SEC);        /* rebase run_time to sec */
>> +    stats->ac_btime = xtime.tv_sec - run_time;
>> +    if (thread_group_leader(tsk)) {
>> +        stats->ac_exitcode = tsk->exit_code;
>> +        if (tsk->flags & PF_FORKNOEXEC)
>> +            stats->ac_flag |= AFORK;
>> +    }
>> +    if (tsk->flags & PF_SUPERPRIV)
>> +        stats->ac_flag |= ASU;
>> +    if (tsk->flags & PF_DUMPCORE)
>> +        stats->ac_flag |= ACORE;
>> +    if (tsk->flags & PF_SIGNALED)
>> +        stats->ac_flag |= AXSIG;
>> +    stats->ac_nice    = task_nice(tsk);
>> +    stats->ac_sched    = tsk->policy;
>> +    stats->ac_uid    = tsk->uid;
>> +    stats->ac_gid    = tsk->gid;
>> +    stats->ac_pid    = tsk->pid;
>> +    stats->ac_ppid    = (tsk->parent) ? tsk->parent->pid : 0;
>> +    stats->ac_utime    = tsk->utime * USEC_PER_TICK;
>> +    stats->ac_stime    = tsk->stime * USEC_PER_TICK;
> 
> 
> I think you should use the portable cputime_xxxx() API since
> tsk->utime and tsk->stime are of type cputime_t

Will fix it.

> 
> 
>> +    /* 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?

Thanks,
  - jay


> 
> 

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