Created attachment 392966 [details, diff] patch to disable avx on amds buldozer family After an update i recognized very slow qt apps. Fist i thought, radeonsi drivers are blame the for that. But after some debuging i found that perf top shows __memcpy_avx_unaligned with a 80& hit ratio. So glibc was eating al the cpu. After digging some more i've read that avx is supported on AMD's Bulldozer architecture but much slower than SSE equivalents. So i patched glibc not to use avx. And .. Hey all back to normal. I've wrote a patch with a additional check to Amd's Bulldozer which disables avx. Please add this patch to glibc patches for glibc-2.20 ebuild. Maybe we should open an upstream bug report also. qt's raster enginge is unusable without it. A mouse over background highlighting needs 2 seconds to happen..... I've tested it with VirtualBox.
Is this related? https://sourceware.org/ml/libc-alpha/2015-01/msg00087.html
https://sourceware.org/ml/libc-alpha/2015-01/msg00087.html could match. I saw that __memcpy_avx_unaligned was the function who it up the cpu. Should i try to the proposed patch ?
(In reply to Eric Grüttefien from comment #2) > https://sourceware.org/ml/libc-alpha/2015-01/msg00087.html could match. I > saw that __memcpy_avx_unaligned was the function who it up the cpu. > > Should i try to the proposed patch ? Please do try it out, so toolchain herd can apply that patch.
Created attachment 395048 [details, diff] [PATCH][BZ #17801] Fix memcpy regression
The mentioned patch [BZ #17801] works also.
this has been fixed in glibc-2.21 we probably should roll it into glibc-2.20 though since it'd be easy
fix is also in glibc-2.20-r2 now
