Re: [pcp] Difference between: kernel.percpu.cpu.user and kernel.pernode.cpu.user

[Mark Goodwin <mgoodwin@xxxxxxxxxx>]

On 11/27/2014 05:17 PM, Shirshendu Chakrabarti wrote:
> Hi PCP team,
>
> Could anyone please respond the question above :)
The difference is the instance domains and counter aggregation.

kernel.pernode is aggregated over all CPUs on each numa node.
On my laptop with 4 CPU cores on one (fake) numa node, we should
expect kernel.all.cpu.user to equal kernel.pernode.cpu.user, and
the sum of the per-cpu counters to equal the same, e.g. :

# pminfo -f kernel.{all,pernode,percpu}.cpu.user

kernel.all.cpu.user
    value 254548080

kernel.pernode.cpu.user
    inst [0 or "node0"] value 254548060

kernel.percpu.cpu.user
    inst [0 or "cpu0"] value 66377110
    inst [1 or "cpu1"] value 61187360
    inst [2 or "cpu2"] value 64051110
    inst [3 or "cpu3"] value 62932480

The mapping between CPUs and nodes is in hinv.map.cpu_node,
where each CPU (instance) is mapped to a node number, e.g.

# pminfo -f hinv.map.cpu_node

hinv.map.cpu_node
    inst [0 or "cpu0"] value 0
    inst [1 or "cpu1"] value 0
    inst [2 or "cpu2"] value 0
    inst [3 or "cpu3"] value 0

In your case, kernel.pernode.cpu.user is zero, which isn't correct.
What platform and PCP version are you running?

Regards
-- Mark

> Thanks,
>
> Shirshendu Chakrabarti
>
> On Wed, Nov 26, 2014 at 3:47 PM, Shirshendu Chakrabarti <shirshendu@xxxxxxx
> <mailto:shirshendu@xxxxxxx>> wrote:
>
>     Hi PCP team,
>
>     Could anyone in the team point me to any literature which explains the
>     difference between a per node metric and percpu metric. The one-liner and
>     extended description are absent in pernode metric case and terse in percpu 
> case.
>
>     For example:
>
>     [root@pcp-test-shir3 pmlogger]# pminfo -f kernel.percpu.cpu.user
>
>     kernel.percpu.cpu.user
>          inst [0 or "cpu0"] value 993240
>     [root@pcp-test-shir3 pmlogger]# pminfo -f kernel.pernode.cpu.user
>
>     kernel.pernode.cpu.user
>          inst [0 or "node0"] value 0
>     I was under the assumption that, kernel.pernode.* and kernel.all.* metrics
>     are the same. I am clearly missing something important.
>
>     Thanks,
>
>     Shirshendu Chakrabarti
>
>
>
>
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