Re: [patch 1/3] basic accounting over taskstats

[Shailabh Nagar <nagar@watson.ibm.com>]

Jay Lan wrote:
> Shailabh Nagar wrote:
> 
>> Andrew Morton wrote:
>>
>>>
>>> Or we remove this field altogether, perhaps.  The same info is available
>>> from /proc/pid/stat anyway.  Is it really needed?
>>>
>>
>> Gathering this data in userspace from /proc might be
>> difficult esp. for short-lived tasks.
> 
> 
> This is a serious concern. I think increasing TS_COMM_LEN
> to 32 would be a good solution.
> 
>>
>> Also, /proc may not be mounted ? I'd heard somewhere that
>> some sysadmins don't install /proc for security reasons.
>> Don't know how far thats true.
>>
>> Several other fields, totalling 58 bytes, added by the CSA
>> patches are also duplicated in /proc/pid/stat. But all of them
>> could change in value during the lifetime of a task so I'm
>> guessing its not useful to get them from /proc
>> even if some kind of userspace polling of the value was
>> possible.
> 
> 
> The same concern above applies to here, doesn't it?

Yes. For some of the fields, pid/ppid/nice/sched you may not
really care about whether you get the value present sometime
during the lifetime vs. value at the time task exited, but for
others like utime/stime/minflt/majflt, getting the last value
is likely to matter. Either way, since there's no guarantee
that you can poll a short-lived task fast enough to get any value,
exporting the value from the kernel at exit seems to be the only safe
way.

--Shailabh

> 
> Regards,
>  - jay
> 
> 
>>
>> But if there is a way, it would sure save a lot of payload
>> sent over taskstats !
>>
>> "duplicate" fields from CSA:
>> +    __u8    ac_nice;        /* task_nice */
>> +    char    ac_comm[TS_COMM_LEN];    /* Command name */
>> +    __u8    ac_sched;        /* Scheduling discipline */
>> +    __u32    ac_pid;            /* Process ID */
>> +    __u32    ac_ppid;        /* Parent process ID */
>> +    __u64    ac_utime;        /* User CPU time [usec] */
>> +    __u64    ac_stime;        /* SYstem CPU time [usec] */
>> +    __u64    ac_minflt;        /* Minor Page Fault */
>> +    __u64    ac_majflt;        /* Major Page Fault */
> 
>