relabelling: Apply of the drop rule before capturing the events

[kakkoyun]

The relabeling functionality we provide prevents the agent from sending profiles if the relabeling configuration specifies a drop fule. We should experiment using this rule to prevent the perf_event from being captured in the first place. This requires us to bring back the target discovery mechanism we had before system-wide profiling and apply relabelling rules before we sync them to the eBPF program. This is just an optimization idea, so we need a baseline to benchmark against the strategy (capture everything and drop afterward), which is yet to be released soon.

Related #690, #7 and #887.

cc @maxbrunet @brancz

[brancz]

This is just an optimization idea, so we need a baseline to benchmark against the strategy (capture everything and drop afterward)

I want to highlight this in particular. My gut feeling is we don’t actually need anything more than this.

The whole point of the Parca project is to profile everything all the time, so this would be the thing that dictates all direction of the project. We may allow other features and ways of using the tool but if this comes at complexity at the burden of the main feature set. I would prefer to have a performance impact on what’s considered non-standard use.