On Wed, May 02, 2018 at 03:56:31PM +0100, Daniel Thompson wrote: > On Wed, May 02, 2018 at 09:44:55PM +0800, changbin.du@xxxxxxxxx wrote: > > From: Changbin Du <changbin.du@xxxxxxxxx> > > > > Hi all, > > I know some kernel developers was searching for a method to dissable GCC > > optimizations, probably they want to apply GCC '-O0' option. But since Linux > > kernel replys on GCC optimization to remove some dead code, so '-O0' just > > breaks the build. They do need this because they want to debug kernel with > > qemu, simics, kgtp or kgdb. > > > > Thanks for the GCC '-Og' optimization level introduced in GCC 4.8, which > > offers a reasonable level of optimization while maintaining fast compilation > > and a good debugging experience. It is similar to '-O1' while perfer keeping > > debug ability over runtime speed. With '-Og', we can build a kernel with > > better debug ability and little performance drop after some simple change. > > > > In this series, firstly introduce a new config CONFIG_NO_AUTO_INLINE after two > > fixes for this new option. With this option, only functions explicitly marked > > with "inline" will be inlined. This will allow the function tracer to trace > > more functions because it only traces functions that the compiler has not > > inlined. > > > > Then introduce new config CONFIG_DEBUG_EXPERIENCE which apply '-Og' > > optimization level for whole kernel, with a simple fix in fix_to_virt(). > > Currently this option is only tested on a QEMU gust and it works fine. > > > > > > Comparison of vmlinux size: a bit smaller. > > > > w/o CONFIG_DEBUG_EXPERIENCE > > $ size vmlinux > > text data bss dec hex filename > > 22665554 9709674 2920908 35296136 21a9388 vmlinux > > > > w/ CONFIG_DEBUG_EXPERIENCE > > $ size vmlinux > > text data bss dec hex filename > > 21499032 10102758 2920908 34522698 20ec64a vmlinux > > > > > > Comparison of system performance: a bit drop (~6%). > > This benchmark of kernel compilation is suggested by Ingo Molnar. > > https://lkml.org/lkml/2018/5/2/74 > > In my mind was the opposite question. When running on the same kernel > does a kernel whose config contains CONFIG_DEBUG_EXPERIENCE build faster > than one without (due to the disabled optimization passes). > > To be honest this is more curiosity than a review comment though... if > you have the figures please share, if not then don't sweat it on my > account! > > > Daniel. > Sorry I don't have the data yet. Per the comment in GCC, I think it should be a little faster but not obviously. > -- Thanks, Changbin Du
