Storing lists of CPU on/off times

Storing lists of CPU on/off times

[Paddie O'Brien]

Hi,

I want to store a per process list of CPU on/off times. So in probe
scheduler.cpu_on I had hoped to do something like:

timestamps[execname()][count] = gettimeofday_us()
count++

This above is illegal but illustrates what I'm trying to do. Can it be done?

Thanks.

Re: Storing lists of CPU on/off times

[William Cohen]

On 01/11/2017 12:24 PM, Paddie O'Brien wrote:
> Hi,
> 
> I want to store a per process list of CPU on/off times. So in probe
> scheduler.cpu_on I had hoped to do something like:
> 
> timestamps[execname()][count] = gettimeofday_us()
> count++
> 
> This above is illegal but illustrates what I'm trying to do. Can it be done?
> 
> Thanks.
> 

Hi,

The cyclethief.stp example does something like that to provide histograms of time a single process is on and off a processor.  (https://sourceware.org/systemtap/examples/process/cycle_thief.txt)

You might take a look at how it is getting that information by looking at the cyclethief.stp script in /usr/share/doc/systemtap*/examples/process/cycle_thief.stp.

-Will

Re: Storing lists of CPU on/off times

[Josh Stone]

On 01/11/2017 09:24 AM, Paddie O'Brien wrote:
> Hi,
> 
> I want to store a per process list of CPU on/off times. So in probe
> scheduler.cpu_on I had hoped to do something like:
> 
> timestamps[execname()][count] = gettimeofday_us()
> count++
> 
> This above is illegal but illustrates what I'm trying to do. Can it be done?

You can't nest the data structure like that, but you *can* use multiple
indexes, like:

    timestamps[execname(), count] = gettimeofday_us()

I'd be wary of execname() for this though, since there could be multiple
processes with the same name.  I suppose that depends on what you need
to do with this data, but pid() is probably a better choice.

Further, you may want to track the scheduling of threads in particular,
since that's the actual unit which is scheduled on/off of CPUs, so then
you'd index by tid().

Re: Storing lists of CPU on/off times

[Paddie O'Brien]

With some post processing I can make timestamps[execname(), count] do
what I need.

Switched to threads as recommended. I can now see that a switch like
vlc ---> vlc was actually a switch between two threads in same
process.

Had a look at cycle_thief.stp but it appears to use an associative
array to map to aggregates which wasn't really what I wanted since it
threw away the individual timestamps.

Thank you.

On 11 January 2017 at 19:06, Josh Stone <jistone@redhat.com> wrote:
> On 01/11/2017 09:24 AM, Paddie O'Brien wrote:
>> Hi,
>>
>> I want to store a per process list of CPU on/off times. So in probe
>> scheduler.cpu_on I had hoped to do something like:
>>
>> timestamps[execname()][count] = gettimeofday_us()
>> count++
>>
>> This above is illegal but illustrates what I'm trying to do. Can it be done?
>
> You can't nest the data structure like that, but you *can* use multiple
> indexes, like:
>
>     timestamps[execname(), count] = gettimeofday_us()
>
> I'd be wary of execname() for this though, since there could be multiple
> processes with the same name.  I suppose that depends on what you need
> to do with this data, but pid() is probably a better choice.
>
> Further, you may want to track the scheduling of threads in particular,
> since that's the actual unit which is scheduled on/off of CPUs, so then
> you'd index by tid().