Hi,
On 20.2.2019 17.32, Marek Olšák wrote:
On Wed, Feb 20, 2019 at 2:31 AM Connor Abbott <cwabbo...@gmail.com
On Wed, Feb 20, 2019 at 4:29 AM Marek Olšák <mar...@gmail.com
...
That's a harsh reaction to a relatively good benchmarking setup.
I use debugoptimized with -DDEBUG. My performance is probably
more affected by -fno-omit-frame-pointer than -DDEBUG.
Why would you enable DEBUG in a profiling build? AFAIK it's supposed
to enable validation more expensive than simple asserts, which you
probably don't want in a benchmarking setup, although from grepping
the source it's not used much. It might be a good idea to move
running NIR validation behind DEBUG instead of !NDEBUG. In the
meantime, unless you really want to benchmark things with assertions
enabled in which case NIR_VALIDATE=0 works (but why would you?), you
can set -Db_ndebug=false in Meson. I just saw today that they're
enabled by default in debugoptimized builds (whoops, better go fix
that and re-profile...).
Assertions and other debug code really don't cost much, so I don't see a
reason to undef DEBUG.
At least on other projects I've seen cases where:
* assert or debug code has been added to places where it's expensive, or
some of those places become expensive later
* one sees low cost code in profiles and assume it to be specific to
DEBUG build, although somebody had forgotten to ifdef it properly
* debug build (or part of it) is compiled with other optimization flags
than release build [1]
* added debug code causes important code not anymore to fit into smaller
cache level (this is very specific to cache sizes on given machine and
code GCC generates though)
[1] Unexpected things happen. Recently I e.g. saw switching
between Meson & Autotools causing Mesa URB allocation changes:
https://bugs.freedesktop.org/show_bug.cgi?id=108787
-> It would help if you could verify what's the perf gap between release
and debug builds, and provide numbers for both (preferably each time
there are significant code changes).
Just using release builds should be simpler though (unless your
intention actually is investigating why debug code is slow).
- Eero
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