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SubjectRe: [PATCH: 2.6.18.1] delayacct: cpu_count in taskstats updated correctly
On Thu, 26 Oct 2006, David Rientjes wrote:
> On Fri, 27 Oct 2006, Martin Tostrup Setek wrote:
>> from: Martin T. Setek <martitse@ifi.uio.no>
>> cpu_count in struct taskstats should be the same as the corresponding (third)
>> value found in /proc/<pid>/schedstat
>
> I disagree in favor of Documentation/accounting/taskstats-struct.txt.
> cpu_count is the number of delay values recorded, so accumulating them is
> appropriate.

Perhaps I'm mistaken, but the code accumulates the value it
finds in sched_info.pcnt in the task_struct. Now, in sched.h I found this:

struct sched_info {
/* cumulative counters */
unsigned long cpu_time, /* time spent on the cpu */
run_delay, /* time spent waiting on a runqueue */
pcnt; /* # of timeslices run on this cpu */

The comment says that these counters are cumulative... The code that
updates them (sched.c: sched_info_arrive()), does accumulate them.

In include/linux/taskstats.h, I found:

* xxx_count is the number of delay values recorded
* xxx_delay_total is the corresponding cumulative delay in nanoseconds

I interpret these comments as saying that:

cpu_delay should be the total number of nanoseconds a task has been
waiting in a runqueue for a CPU, and cpu_count is equal to the number of
times the task got the CPU (or waited for it). If so, then the code
updates taskstats.cpu_delay_total incorrectly too (which my patch didn't
fix).

If not, then the comments in taskstats.h are very confusing....

Martin
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