Re: proposed perf.counter enhancement

[fche at redhat dot com (Frank Ch. Eigler)]

Hi, Stan -


scox wrote:

> [...]
> // Define a perf counter of type X, config Y, sample_freq 0,
> // and task T.  Create a global z[cpu, i] to hold the counters.
> // Does not call _stp_perf_init as perf.type.config does, but calls it
> // later in process.begin
>
> probe perf.type(0).config(0).counter("y")
> {
> }

It would be nice to express per-cpu vs. per-thread counters.

> [...]
> // Define a reading counter probe.  Init the probe for the task:
> // _stp_perf_init (spr_perf_probes[n], task);
> // and generate an implicit read into the counter collector "z", ie
> //  for (i = 0; i < %{ num_online_cpus() %}; i++) {
> //      z[i, z_dims[i]++] = %{ _stp_perf_read(l->l_i) %}

What does the zdims[i]++ part mean?  Is it necessary to read the
counter values across all CPUs?

> // generate implicit read as above the term the counter: _stp_perf_del
> probe process("pwd").end.counter("z")
> {
> }

This doesn't make much sense to me.  The lifetime of some random
process "pwd" would need to spell out the relevance to some counter.


> // generate implicit read for process.function[.return]
> probe process("pwd").function("main").counter("y").counter("z")
> {
> }
>
> probe process("pwd").function("main").return.counter("y").counter("z")
> {
> }

I'd expect these probes to use the z variable somehow, perhaps to save
the deltas in some other array.  Plus, if from probe
perf...counter("z"), the translator understands that z is a special
variable, then perhaps it does not need markup of these counter-user
probes, just the mention of the variables.


> probe process("pwd").function("main").counter("y").counter("z")
> {
>    z <<< perf_read("z")
> }

(Recall though that the problem with a tapset function for this is
being invoked from atomic context.)


> probe end ()
> {
>    foreach (perf in z)
>       printf ("counter[%d] = %d\n", z[perf])
> }

(Wasn't z two-dimensional?)


By contrast, here's how I might imagine a similar scenario looking:

probe perf.type(0).config(0).per_thread("y") { }  # y implicit special local
global history
probe process("foobar").function("*").return { 
      index = tid() # or probefunc()
      history[index] <<< y-@entry(y) 
}
# let implicit global printing take care of [history] stats printing