0.1 contingency plan

Chris Jones jones.chris.g at gmail.com
Tue Nov 12 13:02:49 PST 2013

Howdy, rr is in a somewhat difficult place right now in that we have two
operating modes

1. Pretty fast but unacceptably buggy (syscallbuf; bug is [1]).
2. Pretty stable but slower (no syscallbuf).

Since (1)/[1] is proving hard, I'd like to gauge interest in a contingency
plan built on (2).

I think the two questions are (a) "how stable" and (b) "how slow".  The
stability is beta-quality IMHO.  The slowdown factor depends on workload,
but on a well-mixed (IO and CPU) realistic test case, Firefox startup,
disabling the syscallbuf slows recording down by about 2x.  In a
steady-state browsing session, Firefox is qualitatively less responsive
when the syscallbuf is disabled, but it's hard to quantify that.

My vote is that, if we don't resolve #544 this week, we redefine 0.1 to be
a sort of "slow beta" (0.0 was a slow, buggy alpha ;) ) and ship with the
syscallbuf disabled.  I don't know how to argue it well, but my feeling is
that rr is useful enough now that I could handle offset 2x increased
overhead and rare stability problems.



[1] https://github.com/mozilla/rr/issues/544
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