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To: Mark Wielaard <mjw@redhat.com>
Cc: systemtap@sources.redhat.com
Subject: Re: Pass 4 (non-)optimization speedup
References: <1247337122.2708.24.camel@hermans.wildebeest.org>
From: fche@redhat.com (Frank Ch. Eigler)
Date: Sun, 12 Jul 2009 01:51:00 -0000
In-Reply-To: <1247337122.2708.24.camel@hermans.wildebeest.org> (Mark Wielaard's message of "Sat, 11 Jul 2009 20:32:02 +0200")
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Mark Wielaard <mjw@redhat.com> writes:

> To make pass 4 a bit more flexible I added -O[0123s] as arguments to
> stap (commit 5a5732). [...]
> The default is -O0 which makes pass 4 a lot faster, so I think this is a
> good default. [...]

No, it is unlikely to be a good default.  Frankly, I'm surprised it
even compiles, since some kernel code is unbuildable without
optimization.  Anyway, the code generated by systemtap is complex
enough that with optimization disabled, it is bound to run measurably
slower.  Please test some nontrivial probes with -t before & after.

- FChE