Re: [PATCH 0/9] Trace2 stopwatch timers and global counters

>  3. Rationale
> 
> Timers and counters are an alternative to the existing "region" and "data"
> events. The latter are intended to trace the major flow (or phases) of the
> program and possibly capture the amount of work performed within a loop, for
> example. The former are offered as a way to measure activity that is not
> localized, such as the time spent in zlib or lstat, which may be called from
> many different parts of the program.
> 
> There are currently several places in the Git code where we want to measure
> such activity -- changed-path Bloom filter stats, topo-walk commit counts,
> and tree-walk counts and max-depths. A conversation in [1] suggested that we
> should investigate a more general mechanism to collect stats so that each
> instance doesn't need to recreate their own atexit handling mechanism.
> 
> This is an attempt to address that and let us easily explore other areas in
> the future.
> 
> This patch series does not attempt to refactor those three instances to use
> the new timers and counters. That should be a separate effort -- in part
> because we may want to retool them rather than just translate them. For
> example, rather than just translating the existing four Bloom filter counts
> (in revision.c) into Trace2 counters, we may instead want to have a "happy
> path timer" and a "sad path timer" if that would provide more insight.