On Thu, Mar 03, 2022 at 09:52:50PM -0300, Rogério Valentim Feitoza da Silva wrote: > No kernel should be compiled with compiler optimization, because the compiler > might remove CPU instructions and code that might look "unnecessary" but > are actually required. IIRC a lot of the kernel is compiled with -O2. You could increase it, but it's not necessarily a good idea: On Mon, May 11, 2020 at 05:04:56PM -0700, Linus Torvalds wrote: > I'm not convinced this is sensible. > > -O3 historically does bad things with gcc. Including bad things for > performance. It traditionally makes code larger and often SLOWER. > > And I don't mean slower to compile (although that's an issue). I mean > actually generating slower code. > > Things like trying to unroll loops etc makes very little sense in the > kernel, where we very seldom have high loop counts for pretty much > anything. > > There's a reason -O3 isn't even offered as an option. > > Maybe things have changed, and maybe they've improved. But I'd like to > see actual numbers for something like this. > > Not inlining as aggressively is not necessarily a bad thing. It can > be, of course. But I've actually also done gcc bugreports about gcc > inlining too much, and generating _worse_ code as a result (ie > inlinging things that were behind an "if (unlikely())" test, and > causing the likely path to grow a stack fram and stack spills as a > result). > > So just "O3 inlines more" is not a valid argument. -- https://lore.kernel.org/lkml/CAHk-=wi87j=wj0ijkYZ3WoPVkZ9Fq1U2bLnQ66nk425B5kW0Cw@xxxxxxxxxxxxxx/ On the other hand, decreasing it is also probably not a good idea. Torin _______________________________________________ Kernelnewbies mailing list Kernelnewbies@xxxxxxxxxxxxxxxxx https://lists.kernelnewbies.org/mailman/listinfo/kernelnewbies
