Package: firefox Version: 53.0.is.52.0.2-1 Severity: normal
libyuv which is a performance critical library for firefix is built with -Os which is horrible for performance for it. In particular row_common.cc which contains the generic parts of the color transformation code: See: https://buildd.debian.org/status/fetch.php?pkg=firefox&arch=amd64&ver=53.0.is.52.0.2-1&stamp=1492644908&raw=0 /usr/bin/g++ -std=gnu++11 -o row_common.o -c ... -fPIC -DMOZILLA_CLIENT -include /<<PKGBUILDDIR>>/build-browser/mozilla-config.h -MD -MP -MF .deps/row_common.o.pp -Wdate-time -D_FORTIFY_SOURCE=2 -Wall -Wc++11-compat -Wempty-body -Wignored-qualifiers -Woverloaded-virtual -Wpointer-arith -Wsign-compare -Wtype-limits -Wunreachable-code -Wwrite-strings -Wno-invalid-offsetof -Wc++14-compat -Wno-error=maybe-uninitialized -Wno-error=deprecated-declarations -Wno-error=array-bounds -fno-lifetime-dse -fstack-protector-strong -Wformat -Werror=format-security -fno-schedule-insns2 -fno-lifetime-dse -fno-delete-null-pointer-checks -fno-exceptions -fno-strict-aliasing -fno-rtti -ffunction-sections -fdata-sections -fno-exceptions -fno-math-errno -pthread -pipe -g -freorder-blocks -Os -fomit-frame-pointer /<<PKGBUILDDIR>>/media/libyuv/source/row_common.cc The problematic part is the YuvPixel function which is called in loops and in turn calls tiny clamp functions. Os disables inlining so this causes massive overhead. This is the top cpu profile on sites which e.g. display videos. 17.25% libxul.so [.] YuvPixel ▒ 6.58% libxul.so [.] Clamp ▒ 6.46% libxul.so [.] clamp255 The problem is not as bad as it looks as this generic code is only executed on machines that do not have SSSE3, AVX2 or NEON (see convert_argb.cc) But there are still plenty useful cpus that do not have these instruction sets and are crippled by the compiler flags used. Is it possible to compile this library with O3 to allow the compiler to vectorize it with the best available generic instruction set (e.g. SSE2 on x64). cheers, Julian Taylor
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