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author | bde <bde@FreeBSD.org> | 2008-02-22 17:26:24 +0000 |
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committer | bde <bde@FreeBSD.org> | 2008-02-22 17:26:24 +0000 |
commit | e31bf4b688423b9d648923a471ed8a41940b9432 (patch) | |
tree | c62d1c389f2b51b213bfde9adda1ec07b195e07a /sys/kern/kern_ktrace.c | |
parent | 37c23ae5ff6a87332863506dd6e421e2402a8782 (diff) | |
download | FreeBSD-src-e31bf4b688423b9d648923a471ed8a41940b9432.zip FreeBSD-src-e31bf4b688423b9d648923a471ed8a41940b9432.tar.gz |
Remove the "quick check no cancellation" optimization for
9pi/2 < |x| < 32pi/2 since it is only a small or negative optimation
and it gets in the way of further optimizations. It did one more
branch to avoid some integer operations and to use a different
dependency on previous results. The branches are fairly predictable
so they are usually not a problem, so whether this is a good
optimization depends mainly on the timing for the previous results,
which is very machine-dependent. On amd64 (A64), this "optimization"
is a pessimization of about 1 cycle or 1%; on ia64, it is an
optimization of about 2 cycles or 1%; on i386 (A64), it is an
optimization of about 5 cycles or 4%; on i386 (Celeron P2) it is an
optimization of about 4 cycles or 3% for cos but a pessimization of
about 5 cycles for sin and 1 cycle for tan. I think the new i386
(A64) slowness is due to an pipeline stall due to an avoidable
load-store mismatch (so the old timing was better), and the i386
(Celeron) variance is due to its branch predictor not being too good.
Diffstat (limited to 'sys/kern/kern_ktrace.c')
0 files changed, 0 insertions, 0 deletions