Solaris

Hi all,

Been reading a lot of the cpu load and its "analogy of it to car traffic path of expressway"

From wiki
Most UNIX systems count only processes in the running (on CPU) or runnable (waiting for CPU) states. However, Linux also includes processes in uninterruptible sleep states (usually waiting for disk activity)

q1) what about Solaris (I am on 10) ? Does load include (waiting for disk activity) ?


q2) On a 6 core server , for the past 1 minute -> what does it meant to have a

a) avg load of 6 -- using uptime;
b) cpu idle % of more then 70% ? -- using sar -u 10 6

I issue sar -u 10 6 && uptime (looking at its 1 minute load)

Does it meant that -> for the past 1 minute - my cpu/cores are fully utilized, but the tasks are so simple, the cpu only spent 30% of its time to execute them ?

Regards,
Noob

The load is actually the number of "overdue" threads.
Most obvious is the run queue, threads that are waiting for a free CPU.
But there are threads waiting for something else, e.g. for an I/O driver or another blocked thread. If in user land they show up with state D, but there are also kernel threads that can "pile up" and add to the load.

Hi MadeInGermany,

Thanks for your reply and explanation.

So this bring us back to the question, does Solaris consider process waiting for I/O in (D state) as a load ?

Regards,
Noob

Yes.
And it's an explanation for having high load while CPU is not fully used.

I beg to differ.

There is no D state (uninterruptible) state under Solaris.

My understanding is the S process state (waiting for an event to complete) is not considered as load under Solaris. One or more processes waiting for I/Os to complete do not use any CPU anyway.

Processes in the running and the waiting states (i.e. either using a CPU or runnable but waiting in the run queue) are the only one taken into account.

Hi jlliagre, MadeInGermany

Thanks for all your replies. I believe in linux, IOWait, are actually contributing to the load ( though not reflecting in the run-q ) but Solaris might differ.

Notwithstanding the above, I am trying to understand the co-relationship between cpu-load and cpu utilization

q1) Can I say in a 1 cpu (no core, no hyperthread) environment ->
if the loadavg is 1 (for the last 1 minute) and that 1 thread isn't waiting for any I/O or any other stuff., I would expect to see a near 100% CPU utitlization as well for the last 1 minute?

q2) What could be the scenario whereby i have high amount of load average, but minimum CPU utilization ? (assuming there's no I/O wait).
Could it be the case whereby there are high amount of threads that require CPU time , but getting processed in a very very short time ?

Regards,
Noob

Yes, Linux is well known to include uninterruptible I/O in its load average calculation.

q1) The so called 1 min load average will tend to reach 1 but if the initial load was negligible, you'll need to wait for several minutes for it to get close to 1. It will be about 0.6 instead of 1 after one minute. Reciprocally, if the initial load was higher than one, you'll need to wait long enough (and likely more than 1 minute) to get close enough to it.

q2) The load average is derived from the run queue size which is sampled at 10 ms interval. The CPU load is computed from micro-state accounting with "exact" precision (i.e. several degrees of magnitude better, in the nanosecond range). A dtrace script should allow to figure out what is the cause of the discrepancy but in any case, the CPU utilization values are accurate, the average load is a rough approximation.