Mark Kettenis <[email protected]> writes: >> Date: Sat, 24 Dec 2016 00:08:35 +0100 (CET) >> From: Mark Kettenis <[email protected]> >> >> We already do this on some architectures, but not on amd64 for >> example. The main reason is that this disables memcpy() optimizations >> that have a measurable impact on the network stack performance. >> >> We can get those optimizations back by doing: >> >> #define memcpy(d, s, n) __builtin_memcpy((d), (s), (n)) >> >> I verified that gcc still does proper bounds checking on >> __builtin_memcpy(), so we don't lose that. >> >> The nice thing about this solution is that we can choose explicitly >> which optimizations we want. And as you can see the kernel makefile >> gets simpler ;). >> >> Of course the real reason why I'm looking into this is that clang >> makes it really hard to build kernels without -ffreestanding. >> >> The diff below implements this strategy, and enabled the optimizations >> for memcpy() and memset(). We can add others if we think there is a >> benefit. I've tested the diff on amd64. We may need to put an #undef >> memcpy somewhere for platforms that use the generic C code for memcpy. >> >> Thoughts? > > So those #undefs are necessary. New diff below. Tested on armv7, > hppa and sparc64 now as well.
I think this is the way to go; can't help tests on other archs, though. ok jca@ fwiw -- jca | PGP : 0x1524E7EE / 5135 92C1 AD36 5293 2BDF DDCC 0DFA 74AE 1524 E7EE
