On Thu, 01 Dec 2022 15:29:41 -0500 Rik van Riel <riel@xxxxxxxxxxx> wrote: > On Thu, 2022-12-01 at 19:33 +0100, Thorsten Leemhuis wrote: > > Hi, this is your Linux kernel regression tracker. > > > > On 28.11.22 07:40, Nathan Chancellor wrote: > > > Hi Rik, > > > > I wonder what we should do about below performance regression. Is > > reverting the culprit now and reapplying it later together with a fix > > a > > viable option? Or was anything done/is anybody doing something > > already > > to address the problem and I just missed it? > > The changeset in question speeds up kernel compiles with > GCC, as well as the runtime speed of other programs, due > to being able to use THPs more. However, it slows down kernel > compiles with clang, due to ... something clang does. > > I have not figured out what that something is yet. > > I don't know if I have the wrong version of clang here, > but I have not seen any smoking gun at all when tracing > clang system calls. I see predominantly small mmap and > unmap calls, and nothing that even triggers 2MB alignment. 2.8% speedup for gcc is nice. Massive slowdown in the malloc banchmark and in LLVM/clang is very bad - we don't know what other userspace will be so affected. So I think we revert until this is fully understood.
