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Torvalds Is Unconvinced By LTO'ing A Linux Kernel

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  • #61
    Originally posted by Brane215 View Post
    And WEEKS of lost time, mopping the cr*p afteer each such gain have lost me half of lifetime already. And it is adding up infinitely faster.
    Doing it for testing is fine, but using this in kernel for 1% gain on some irellevant test for 99.999% of the planet while risking for the thing to ge berserk and make fruit salad out of one's disk/s/ is IMHO moronic.
    Nobody said LTO is going to be FORCED in the kernel. It would probably be quite the opposite.

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    • #62
      The promised numbers on LTO and FIrefox http://hubicka.blogspot.ca/2014/04/l...2-firefox.html

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      • #63
        LTO option sounds nice for release kernels of distributions (because generally you don't wanna wait hours for kernel to build while consuming a _lot_ of ram).
        I tried building my custom kernel with LTO and it ate 3GB of ram (and my kernel is fairly slim - stripped of unneeded modules).
        I dont think my 8gb of ram would suffice for allconfig, though patches seem to have mitigated ram usege to some extent (firefox LTO build takes 7gigs easily on 64bit).

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        • #64
          Originally posted by tpruzina View Post
          LTO option sounds nice for release kernels of distributions (because generally you don't wanna wait hours for kernel to build while consuming a _lot_ of ram).
          I tried building my custom kernel with LTO and it ate 3GB of ram (and my kernel is fairly slim - stripped of unneeded modules).
          I dont think my 8gb of ram would suffice for allconfig, though patches seem to have mitigated ram usege to some extent (firefox LTO build takes 7gigs easily on 64bit).
          With building Android with LTO, I've noticed that it'll just use as much RAM as it can, with more RAM available it takes less time but it doesn't seem to fail or anything when there is less RAM available. This leads me to believe that available RAM with LTO isn't really a problem, at least when you get past 4GB or so.

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          • #65
            BTW, I have noticed on Jan Hubicka's blog that LTO brings most benefits when used with aggressive optimisations like -O3 and profiling driven optimisation.

            So it would be nice to have that option with kernel, too. If it wouldn't break anything.

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            • #66
              Originally posted by Brane215 View Post
              BTW, I have noticed on Jan Hubicka's blog that LTO brings most benefits when used with aggressive optimisations like -O3 and profiling driven optimisation.

              So it would be nice to have that option with kernel, too. If it wouldn't break anything.
              How would you PGO the kernel so that it doesn't become slow for some case you didn't test?

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