I've been using lto for the past several weeks not for performance reasons but to reduce the resulting binary size which has grown to be rather substantial. I usually set "-flto -ffat-lto-objects -flto-odr-type-merging" in the CFLAGS and CXXFLAGS env vars prior to configure and have yet to experience any problems with the files in mapi./
- Chuck On Tue, May 31, 2016 at 3:42 AM, Eero Tamminen <eero.t.tammi...@intel.com> wrote: > Hi, > > On 30.05.2016 20:57, Rob Clark wrote: > >> On Mon, May 30, 2016 at 1:39 PM, Matt Turner <matts...@gmail.com> wrote: >> >>> On Mon, May 30, 2016 at 10:28 AM, ⚛ <0xe2.0x9a.0...@gmail.com> wrote: >>> >>>> This patch enables compilation with -flto. >>>> >>>> The performance benefits of LTO (GCC 4.9 & 6.1) are about 1% for >>>> glxgears. >>>> Performance changes in OpenGL games haven't been measured yet, my >>>> feeling is >>>> that they are negligible. >>>> >>> >>> Without a compelling reason, I don't think the build system should be >>> adding compiler flags like this. >>> >>> -flto makes debugging impossible, at least the last time I tried it >>> with gcc. I don't think that's something we would want enabled >>> whenever it's supported. >>> >> >> It would be interesting to know what gains it brings in scenarios less >> synthetic than glxgears.. my suspicion is that we have been doing >> manual lto forever (ie. use of static-inline fxn's where it matters). >> If it turns out to be a significant gain, I wouldn't be against it. >> Although perhaps only for non-debug builds.. >> > > Martin did some testing with LTO last year for a real customer 3D > benchmark that was partly CPU bound. In that case there were actually > several percent performance improvements. > > How much, depends on: > - How CPU bound the 3D benchmark is and do those CPU bottlenecks hit cases > where LTO can actually help > - What's the CPU/GPU balance on the given given HW > (more visible on more CPU bound HW) > - What GCC version is used > (newer GCC versions provide more benefit with LTO) > > And it should not hurt performance (at least if one is using "performance" > frequency policy, or fixed CPU frequency, instead of "powersave" one. > "Powersave" can drop CPU frequency dramatically when use-case drop its CPU > usage and large enough CPU freq drop can make things slower). > > > - Eero > > > _______________________________________________ > mesa-dev mailing list > mesa-dev@lists.freedesktop.org > https://lists.freedesktop.org/mailman/listinfo/mesa-dev >
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