( )⚙ D4344 tracing: new module to make tracing events in hg easier

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tracing: new module to make tracing events in hg easier
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Authored by durin42 on Aug 21 2018, 5:39 PM.

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Summary

This lives in hgdemandimport because I want to instrument a bunch of
low-level stuff including the bare hg script and demandimport, so it
can't live at a higher layer.

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durin42 created this revision.Aug 21 2018, 5:39 PM
indygreg added inline comments.
hgdemandimport/tracing.py
31–34

Per my comment in D4342, I think we should consider recording the timing from here so times aren't skewed due to the presence of pipe I/O. That will introduce some overhead in the traced process. But such is the price to be paid for accurate time reporting, I suppose.

This revision was automatically updated to reflect the committed changes.

Per my comment in https://phab.mercurial-scm.org/D4342 https://phab.mercurial-scm.org/D4342, I think we should consider recording the timing from here so times aren't skewed due to the presence of pipe I/O. That will introduce some overhead in the traced process. But such is the price to be paid for accurate time reporting, I suppose.

My thinking on that was to avoid the syscall overhead for getting timestamps in the main hg process, which we’ve seen be a huge drag on performance. I couldn’t think of anything cheaper than a single string interpolation and a write to a named pipe, so that’s what we’ve got for now - we can always pursue more in the future if we want, but I want this tracing to be cheap enough that I could plausibly turn it on for 1% of invocations )or whatever) and not have users notice.