Proposed systemtap access to perfmon hardware

[Stone, Joshua I]

William Cohen wrote:
> As far as when the performance counters are set up and torn down it
> seems like it would be most reasonable to set them up before the first
> probe begin action and tear them down after the last probe end action.

I agree

> This would mean for sampling would need to have it stop sampling if
> don't want any additional samples while doing the probe end action.

This should be gated for you by using the session_state.  Begin probes
only run during STAP_SESSION_STARTING, normal probes (including permon
sampling) should only run during STAP_SESSION_RUNNING, and end probes
only run during STAP_SESSION_STOPPING.  If a probe is entered during a
state that doesn't match what it expects, it just returns with out
taking any action.


Josh