Re: [linuxtools-dev] [TMF] Advanced statistics view

[Alexandre Montplaisir <alexmonthy@xxxxxxxxxxxx>]

Hi François,

This would indeed be a nice addition. It would require storing more data
in the state system compared to what we have now (and I'm not sure if it
would "partializable", probably but we would have to check for corner
cases).


We did an experiment about this a couple weeks back, it's a bit tricky
how to store this information in the state system, but after a couple
iterations we found out that the probably easiest way is to:

- When a process arrives on the CPU, insert a state change whose value
represents the *current*, at that time, cumulative amount of CPU time
for that process.
- When the process leaves, insert a null value to indicate it's not on
the CPU anymore. The value of the interval that will be created will
still be the cumulative CPU time at the *beginning* of the interval.
- When the process comes back, you can get its latest cumulative CPU
time by querying "two intervals back", and adding the length of that
interval to update the cumulative time. You insert a change with that
value, etc.
Rinse and repeat for every process (or resource) you want to track.

When doing queries:
- If you fall on a "real" interval, you know you are in a time where the
process was active on the CPU. You will need to do the interpolation
between the value (which represents the cumulative amount at the start
of the interval), the length of the interval, and the current position
in the interval itself. Note this does not require any extra query to
the state system, because a query returns you the whole interval now.
- If you fall on a null value, this means the process was not on the
CPU. To get its cumulative CPU time, get the previous interval (query at
"interval.startTime - 1"), get the value of that interval + its length.
This will give you the cumulative time at the end of that interval,
which stays constant for the whole null interval too.

Hoping it makes sense ;)
Other ways could require storing in RAM the current total per
process/per CPU, or doing back-assignments of states. But the above
method doesn't need any of that.

We only brainstormed about this, no implementation was done so far. If
you would like to experiment on adding this to the state system and the
statistics view, we'd be happy to review it ;)


Cheers,

--
Alexandre Montplaisir
Eclipse Linux Tools committer





On 13-02-11 12:06 PM, François Rajotte wrote:
> Hello all,
>
> I have some questions about the current state of the statistics viewer
> inside TMF.
>
> Recent developments have integrated the state system to the statistics
> view in order to speed up the queries.
> At the moment, the information stored in this state system consists
> solely of raw event count.
>
> It seems to me that more advanced statistics could be displayed using
> the same view and basic framework.
> For kernel traces, I feel like CPU usage per process would be a very
> interesting statistic to show||.
>
> The structure could look like this :
>
> Process #1 : 25% total
>     -> CPU0 : 20%
>     -> CPU1 : 5%
>
> Process #2 : 10% total
>     -> CPU0 : 10%
>     -> CPU1 : 0%
>
> We could also want the complementary information:
>
> CPU0 : 30% total
>     -> Process #1 : 20%
>     -> Process #2 : 10%
>
> CPU1 : 5% total
>     -> Process #1 : 5%
>     -> Process #2 : 0%
>
> I would like to have the developers' opinion on this. Are similar
> features planned or have been discussed in the past? What major
> hurdles do you see?
>
> As a user, I feel like this would greatly benefit the control flow view.
>
> Thanks,
> François
>
>