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authorLinus Torvalds <torvalds@linux-foundation.org>2010-01-12 18:16:42 -0800
committerH. Peter Anvin <hpa@zytor.com>2010-01-13 22:39:50 -0800
commitbafaecd11df15ad5b1e598adc7736afcd38ee13d (patch)
tree99b676d1ecc202358fe67acd095aa2c1f1ef2b1f /arch/um
parent5d0b7235d83eefdafda300656e97d368afcafc9a (diff)
x86-64: support native xadd rwsem implementation
This one is much faster than the spinlock based fallback rwsem code, with certain artifical benchmarks having shown 300%+ improvement on threaded page faults etc. Again, note the 32767-thread limit here. So this really does need that whole "make rwsem_count_t be 64-bit and fix the BIAS values to match" extension on top of it, but that is conceptually a totally independent issue. NOT TESTED! The original patch that this all was based on were tested by KAMEZAWA Hiroyuki, but maybe I screwed up something when I created the cleaned-up series, so caveat emptor.. Also note that it _may_ be a good idea to mark some more registers clobbered on x86-64 in the inline asms instead of saving/restoring them. They are inline functions, but they are only used in places where there are not a lot of live registers _anyway_, so doing for example the clobbers of %r8-%r11 in the asm wouldn't make the fast-path code any worse, and would make the slow-path code smaller. (Not that the slow-path really matters to that degree. Saving a few unnecessary registers is the _least_ of our problems when we hit the slow path. The instruction/cycle counting really only matters in the fast path). Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org> LKML-Reference: <alpine.LFD.2.00.1001121810410.17145@localhost.localdomain> Signed-off-by: H. Peter Anvin <hpa@zytor.com>
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