I know that mpstat uses /proc/stat to gather it's data and pidstat uses
/proc/<pid>/stat to get it's data so they are kind of looking at
different info. The mpstat is looking at the cpustat structure in the
kernel and the pidsat is looking at the data inside each task structure.
I get a situation once in a while where things don't seem to add up:
# mpstat -P 4 1
05:34:51 CPU %user %nice %sys %iowait %irq %soft
%steal %idle intr/s
05:34:51 4 0.00 0.00 0.00 0.00 0.00 0.00
0.00 100.00 525.00
05:34:52 4 0.00 0.00 0.00 0.00 0.00 0.00
0.00 100.00 533.00
05:34:53 4 0.00 0.00 0.00 0.00 0.00 0.00
0.00 100.00 508.00
05:34:54 4 0.99 0.00 0.00 0.00 0.00 0.00
0.00 99.01 512.00
05:34:55 4 0.00 0.00 0.00 0.00 0.00 0.00
0.00 100.00 1010.00
05:34:56 4 0.99 0.00 0.99 0.00 0.99 0.00
0.00 97.03 751.00
05:34:57 4 0.00 0.00 0.00 0.00 0.00 0.00
0.00 100.00 746.00
05:34:58 4 0.00 0.00 0.00 0.00 0.00 0.00
0.00 100.00 762.00
05:34:59 4 0.00 0.00 0.00 0.00 0.00 0.00
0.00 100.00 642.00
# pidstat -p 2358 -p 592 -p 3607 -p 2362 -p 2324 -u 1
05:34:51 PID %user %system %CPU CPU Command
05:34:52 2358 2.00 0.00 2.00 4 prog1
05:34:52 592 2.00 0.00 2.00 4 prog2
05:34:52 3607 10.00 2.00 12.00 4 prog3
05:34:52 2362 0.00 0.00 0.00 4 prog4
05:34:52 2324 0.00 0.00 0.00 8 prog5
05:34:52 PID %user %system %CPU CPU Command
05:34:53 2358 0.00 0.00 0.00 4 prog1
05:34:53 592 2.00 0.00 2.00 4 prog2
05:34:53 3607 12.00 3.00 15.00 4 prog3
05:34:53 2362 0.00 0.00 0.00 4 prog4
05:34:53 2324 0.00 0.00 0.00 8 prog5
05:34:53 PID %user %system %CPU CPU Command
05:34:54 2358 0.00 0.00 0.00 4 prog1
05:34:54 592 6.00 1.00 7.00 4 prog2
05:34:54 3607 7.00 2.00 9.00 4 prog3
05:34:54 2362 0.00 0.00 0.00 4 prog4
05:34:54 2324 0.00 0.00 0.00 8 prog5
05:34:54 PID %user %system %CPU CPU Command
05:34:55 2358 0.00 0.00 0.00 4 prog1
05:34:55 592 2.00 1.00 3.00 4 prog2
05:34:55 3607 10.00 3.00 13.00 4 prog3
05:34:55 2362 0.00 0.00 0.00 4 prog4
05:34:55 2324 0.00 0.00 0.00 8 prog5
05:34:55 PID %user %system %CPU CPU Command
05:34:56 2358 0.00 1.00 1.00 4 prog1
05:34:56 592 7.00 0.00 7.00 4 prog2
05:34:56 3607 12.00 2.00 14.00 4 prog3
05:34:56 2362 0.00 0.00 0.00 4 prog4
05:34:56 2324 0.00 0.00 0.00 8 prog5
05:34:56 PID %user %system %CPU CPU Command
05:34:57 2358 0.00 0.00 0.00 4 prog1
05:34:57 592 1.00 1.00 2.00 4 prog2
05:34:57 3607 15.00 3.00 18.00 4 prog3
05:34:57 2362 0.00 0.00 0.00 4 prog4
05:34:57 2324 0.00 0.00 0.00 8 prog5
05:34:57 PID %user %system %CPU CPU Command
05:34:58 2358 2.00 0.00 2.00 4 prog1
05:34:58 592 5.00 1.00 6.00 4 prog2
05:34:58 3607 11.00 3.00 14.00 4 prog3
05:34:58 2362 0.00 0.00 0.00 4 prog4
05:34:58 2324 0.00 0.00 0.00 8 prog5
These processes are tied to processor 4.
You'll see that mpstat shows 0% user while prog3 shows as much as 10% or
12% in some of the corresponding intervals.
From looking in the kernel is seems this routine increments both the
task utime used by pidstat and the cpustat used by mpstat.
/*
* Account user cpu time to a process.
* @p: the process that the cpu time gets accounted to
* @cputime: the cpu time spent in user space since the last update
*/
void account_user_time(struct task_struct *p, cputime_t cputime)
{
struct cpu_usage_stat *cpustat = &kstat_this_cpu.cpustat;
cputime64_t tmp;
p->utime = cputime_add(p->utime, cputime);
/* Add user time to cpustat. */
tmp = cputime_to_cputime64(cputime);
if (TASK_NICE(p) > 0)
cpustat->nice = cputime64_add(cpustat->nice, tmp);
else
cpustat->user = cputime64_add(cpustat->user, tmp);
/* Account for user time used */
acct_update_integrals(p);
}
This essentially gets called from tick_periodic(), which I assume gets
called each tick, from the update_process_times() routine which calls
the account_process_tick() routine which calls the above routine, if
it's in userspace at the tim eof the tick or a corresponding
account_system_time() routine if it is in the kernel at the time of the
tick.
I believe the p->utime = sputime_add() increments the task structure
that pidstat uses and cpustat->user|nice = cputime64_add() increments
the cpustat that mpstat looks at. This seems like the only palce in the
kernel where the task utime gets incemented or the cpustat user time
gets incremented.
The data shows that the specific process times are as much as 10% but
the overall is 0%.
How can this happen if these get incremented together in this one place?
What am I missing ?
Thanks
Chris Kottaridis
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