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Date: Sun, 17 Oct 2021 11:32:38 -0700 From: Randy Dunlap <rdunlap@...radead.org> To: Julia Lawall <julia.lawall@...ia.fr>, linux-kernel@...r.kernel.org, Masahiro Yamada <masahiroy@...nel.org>, Michal Marek <michal.lkml@...kovi.net>, linux-kbuild@...r.kernel.org Subject: Re: build reproducibility 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. I say this only because sometimes I cannot even reproduce a build that has errors or warnings unless I prefix it with make clean or mrproper. (i.e., nothing to do with booting and running the new kernel) Even though the .config file has changed and I do "make olddefconfig", the same build errors do not show up unless I do the clean or mrproper step also. -- ~Randy
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