On Wed, Feb 19, 2020 at 9:45 AM Christophe Leroy <christophe.le...@c-s.fr> wrote: > Le 16/02/2020 à 19:10, Arnd Bergmann a écrit : > > On Sat, Jan 11, 2020 at 12:33 PM Segher Boessenkool > > <seg...@kernel.crashing.org> wrote: > >> > >> On Fri, Jan 10, 2020 at 07:45:44AM +0100, Christophe Leroy wrote: > >>> Le 09/01/2020 à 21:07, Segher Boessenkool a écrit : > >>>> It looks like the compiler did loop peeling. What GCC version is this? > >>>> Please try current trunk (to become GCC 10), or at least GCC 9? > >>> > >>> It is with GCC 5.5 > >>> > >>> https://mirrors.edge.kernel.org/pub/tools/crosstool/ doesn't have more > >>> recent than 8.1 > >> > >> Arnd, can you update the tools? We are at 8.3 and 9.2 now :-) Or is > >> this hard and/or painful to do? > > > > To follow up on this older thread, I have now uploaded 6.5, 7.5, 8.3 and 9.2 > > binaries, as well as a recent 10.0 snapshot. > > > > Thanks Arnd, > > I have built the VDSO with 9.2, I get less performant result than with > 8.2 (same performance as with 5.5). > > After a quick look, I see: > - Irrelevant NOPs to align loops and stuff, allthough -mpcu=860 should > avoid that. > - A stack frame is set for saving r31 in __c_kernel_clock_gettime. GCC > 8.1 don't need that, all VDSO functions are frameless with 8.1
If you think it should be fixed in gcc, maybe try to reproduce it in https://godbolt.org/ and open a gcc bug against that. Also, please try the gcc-10 snapshot, which has the highest chance of getting fixes if it shows the same issue (or worse). Arnd
