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"CC_OPTIMIZE_FOR_PERFORMANCE_O3" Performance Tunable Dropped In Linux 6.0

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  • "CC_OPTIMIZE_FOR_PERFORMANCE_O3" Performance Tunable Dropped In Linux 6.0

    Phoronix: "CC_OPTIMIZE_FOR_PERFORMANCE_O3" Performance Tunable Dropped In Linux 6.0

    Following recent upstream discussions around the -O3 compiler optimizations for the Linux kernel, the Kconfig switch advertising this option is being removed in Linux 6.0...

    https://www.phoronix.com/news/Linux-...ops-O3-Kconfig

  • #2
    Gonna get some popcorn and then watch the forum argue over this one.

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    • #3
      Originally posted by NotMine999 View Post
      Gonna get some popcorn and then watch the forum argue over this one.
      same 🍿🍿🍿

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      • #4
        Clear Linux is now using -O3: https://github.com/clearlinux-pkgs/l...174df7ef77e4e4

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        • #5
          my -O3 Linux kernel build benchmarks from this summer didn't show it to be particularly worthwhile.
          I think this needs to be judged on the amount of effort. Show me anything else which can deliver a couple % gains by just flipping a switch.

          And I maintain that it's just a starting point. If some careful analysis is done to see where -O3 helps vs. hurts or which options & parameters implied by -O3 are actually delivering most of the gains, then there's even further potential for performance improvements.

          Or, we could just continue to compile like it's 1999 ...for the rest of time.

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          • #6
            You'd better worry about .0 versions, because they can eat your data ... Any other pervercy like -O3, -march=native or GCC LTO should be fine and will only affect performance in worst case.
            Source: longtime GentooLTO overlay user.

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            • #7
              Other upstream kernel developers also criticized that higher optimization level over the default -O2 level due to the risks, particularly with older compilers and memories from times when -O3 tended to be more buggy.
              They're playing the Incel Card?

              When I was younger I gained some bad memories of girls, especially older women, being scary to talk to and rejecting me so I now don't talk to them even though 28 years have passed.

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              • #8
                Like anything, someone has to take the 1st steps to use -O3 a LOT. Beat the hell out of O3 from all angles. Find those pesky corner cases. Fuzz, if possible, the crap out of O2 and then O3 and compare side by side. I'm no compiler expert but at the very least, it requires years of people beating on it but, most importantly, reporting results and errors. I don't know how mature the O3 options are as compared to O2 but from reading Phoronix for a decade plus, it seems folks have mixed results depending on the application it's targeting. Get -O2 running as close to perfect before you go heralding or cursing what O3 can bring to the table. It seems it still needs some more time to mature and develop. It's not worth losing data to score a couple more % of perf.

                If Clear Linux is indeed leveraging O3 a lot, they've probably hit some of the odd effects and behaviors people have talked about. I just hope they're reporting those effect and, if they can be fixed, contributing fixes to stabilize that O3 feature. Maybe GCC 13/14 will be in better shape with O3.

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                • #9
                  Originally posted by coder View Post
                  I think this needs to be judged on the amount of effort. Show me anything else which can deliver a couple % gains by just flipping a switch.

                  And I maintain that it's just a starting point. If some careful analysis is done to see where -O3 helps vs. hurts or which options & parameters implied by -O3 are actually delivering most of the gains, then there's even further potential for performance improvements.

                  Or, we could just continue to compile like it's 1999 ...for the rest of time.
                  So they are giving the easy option to enable -O3 if you want ... or there are apparently distros doing just that so just use that distro and be done with it. Me, personally, I am paid to develop solutions, and no part of that is debugging edge-case kernel crashes. I want stability...period, and I will always take guidance from the people who own the code because they know far more than myself how to best use their product.

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                  • #10
                    Originally posted by insilications View Post
                    Maybe O3 is beneficial if vectorization is switched off? That's at least what the patch suggests. I'm not saying that it is a validating proof. But clear Linux devs have shown quite some history of pushing good optimisations to Linux.

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