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From Fraser Adams <fraser.ad...@blueyonder.co.uk>
Subject Re: Qpid's move to CMake and effect on performance.
Date Mon, 27 Jan 2014 20:25:59 GMT
On 27/01/14 15:06, Andrew Stitcher wrote:
> I think that (too lazy to actually go look) in autotools the build
> default was -O2 and the Fedora/RHEL packaging set -O3.
>
> It is completely true that with cmake we've opted to follow the usual
> cmake practice (which is standard on Windows too) of having the build
> configuration dictate the optimisation/debug flags. I think that in the
> Fedora/RHEL packages we now use the RelWithDebInfo build configuration
> which corresponds to -O2 -g.
>
> It is true that if you specify no CMAKE_BUILD_TYPE then you will get no
> optimisation or debug flags set which is perhaps a rather bad idea.
>
> What do you think the default build type should be? (Out of Debug = -g,
> Release = -O2 -DNDEBUG, RelWithDebInfo -O2 -DNDEBUG -g, MinSizeRel = -Os
> -DNDEBUG)
>
> It's not clear to me that we should prioritise performance over
> debugability in our default build.
>
> Andrew
>
Thanks for the response Andrew - glad I'm not going mad :-D

I think that I'm *relatively* agnostic as to what the default should be, 
but I definitely think that this stuff should be included in the 
build/install instructions for qpid/proton/dispatch/etc. If you've got 
familiarity with CMake it might be second nature, but I don't think we 
should assume this (I only figured it out by accident, having only 
fairly rudimentary CMake experience).

Out of curiosity looking at the list above I don't see an option that 
does "-O3" what would that be? I'd like to eke the maximum performance 
out of the components I'm running operationally - we've got some very 
high throughput use cases so I'm keen to make sure that we don't hit 
performance regressions as we upgrade from earlier Qpid versions.

Cheers,
Frase



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