Opened 13 years ago

Closed 13 years ago

Last modified 13 years ago

#3271 closed Enhancement (fixed)

Don't override user compiler optimization flags

Reported by: Astara Owned by: charles
Priority: Low Milestone: 2.00
Component: Transmission Version: 1.93
Severity: Minor Keywords: development, optimization, compiler


When I looked at the optimization in doing local builds, I noted it was set for -O3. I've would like to suggest a slightly different option and some default tuning options. Some of the -O3 options can result in worse performance due to their using more memory and possibly hurting cache performance. Thus, in the kernel, they generally try to use -O2 and add further optimizations that won't increase memory usage. In my own use I add switches to allow unrolling some invariant code in loops, figuring it is small, but probably worth the faster code.

Specifically, I've been using (-O2 +..) -fbranch-target-load-optimize2 -fgcse -fgcse-las -fgcse-lm -f gcse-sm -fpredictive-commoning -frename-registers -fstack-protector -ftracer -ftree-loop-distribution -ftree-vectorize -funswitch-loops -funwind-tables -fvariable-expansion-in-unroller -fvpt -fweb

For my own builds I use -march=native, but that assumes that you are running on the same arch as you build on (true for me, but maybe not in general).

Change History (5)

comment:1 Changed 13 years ago by charles

Reading through the thread in it makes me wonder if we'd be better off removing those optimization settings altogether since the packagers, builders, and installers know their platforms better than autoconf does.

comment:2 Changed 13 years ago by charles

  • Milestone changed from None Set to 2.00
  • Owner set to charles
  • Status changed from new to assigned
  • Summary changed from RFE .. suggest different optimization options on linux to Don't override user compiler optimization flags

comment:3 Changed 13 years ago by charles

  • Resolution set to fixed
  • Status changed from assigned to closed

Fixed in trunk for 2.00 by r10733

comment:4 Changed 13 years ago by Astara

...but this doesn't indicate what is done in the default case where the user has not specified options... -O3 isn't the best choice for a default. -O2 + [some option set, possibly 'null] might be more prudent.

comment:5 Changed 13 years ago by charles

autoconf uses "-g -O2" by default because it is known to be safe on the majority of platforms and therefore is likely to be safe as a compromise between "optimization" and "non-optimization".

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