On Mon, Oct 18, 2021 at 3:42 AM Julia Lawall <julia.lawall@xxxxxxxx> wrote: > > > > On Sun, 17 Oct 2021, Randy Dunlap wrote: > > > On 10/17/21 11:12 AM, Julia Lawall wrote: > > > Hello, > > > > > > If I do the following: > > > > > > git clean -dfx > > > cp saved_config .config > > > make olddefconfig && make && make modules_install && make install > > > > > > Should I always end up with the same kernel, regardless of the kernel that > > > is currently running on the machine? > > > > > > I see a large performance difference between Linux 5.10 and all versions > > > afterwards for a particular benchmark. I am unable to bisect the problem > > > eg between 5.10 and 5.11, because as soon as I come to a kernel that gives > > > the bad performance, all of the kernels that I generate subsequently in > > > the bisecting process (using the above commands) also have the bad > > > performance. > > > > > > It could of course be that I have completely misinterpreted the problem, > > > and it has nothing to do with the kernel. But I have tested the program a > > > lot when only working on variants of Linux 5.9. I only start to have > > > problems when I use versions >= 5.11. > > > > Hi, > > > > My "guess" is that this has something to do with the build > > reusing some current file(s) that need to be rebuilt. > > I.e., adding a "make clean" or "make proper" might be needed. > > This was my guess too. But I have the git clean -dfx. I did a comparison > with make distclean and this does a little more (mostly some files in > tools). > > thanks, > julia > 'git clean -dfx' is a very hard cleaning. So, you are doing a full build in every step of bisecting. I have no idea to explain the symptom you observed: "as soon as I come to a kernel that gives the bad performance, all of the kernels that I generate subsequently in the bisecting process" If you desire perfect reproducibility, you can check Documentation/kbuild/reproducible-builds.rst But, I doubt slight differences such as timestamps can explain the large performance difference. If you are chasing the performance issue, commit cf536e185869d4815 said CONFIG_DEBUG_FORCE_FUNCTION_ALIGN_* might be useful to eliminate the possibility of code alignment. Otherwise, I have no more idea... -- Best Regards Masahiro Yamada
