On 16 August 2012 13:04, Mans Rullgard <[email protected]> wrote: > On 15 August 2012 22:38, Mans Rullgard <[email protected]> wrote: >> On 15 August 2012 17:17, Matthew Gretton-Dann >> <[email protected]> wrote: >>> The performance of PGO on 'a popular embedded benchmark' is 14% >>> improvement, LTO is 7%. Don't know both together, or SPEC. >> >> On 'a popular media coding library' PGO gains 2-5% in general, in one case >> as much as 11%. The relative gains are larger on average with hand-written >> assembly disabled, but obviously nowhere near the performance with it >> enabled. >> >> On the same library LTO is 2-3.5 _times_ slower than without on all tests, >> although it does pass the test suite. > > Sorry for crying wolf. I redid the LTO build and the huge performance drop is > gone. Now I'm getting minor gains on most tests and 5-8% loss on a few. More > worrying is that it is now failing a few tests. I'll look into both issues > and report back.
The test failures are caused by a known bug in 4.8 trunk (54132). After hacking the build system to make sure exactly the same optimisation flags are used when compiling and linking, I'm getting a 4% gain as best result and 1% loss on a couple of tests. Most tests change less than 1%. If the optimisation flags for compiling and linking differ, all kinds of bad things seem to happen. -- Mans Rullgard / mru _______________________________________________ linaro-toolchain mailing list [email protected] http://lists.linaro.org/mailman/listinfo/linaro-toolchain
