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| author | Kaleb S. KEITHLEY <kkeithle@redhat.com> | 2019-03-28 09:36:33 -0400 |
|---|---|---|
| committer | Shyamsundar Ranganathan <srangana@redhat.com> | 2019-04-16 10:48:06 +0000 |
| commit | 27a96f1f344d16de8085ace40c2be99c3cd83139 (patch) | |
| tree | b7f9303f6d5d6e147860948687282e1f7dea6c60 | |
| parent | c5bc21ebbc10248848b372db34a33a0fcb9ae2ae (diff) | |
rpclib: slow floating point math and libm
In release-6 rpc/rpc-lib (libgfrpc) added the function
get_rightmost_set_bit() which calls log2(3), a call that takes
a floating point parameter and returns a floating point.
It's used thusly:
right_most_unset_bit = get_rightmost_set_bit(...);
(So is it really the right-most unset bit, or the right-most set bit?)
It's unclear to me whether this is in the data path or not. If it is,
it's rather scary to think about integer-to-float and float-to-integer
conversions and slow calls to libm functions in the data path.
gcc and clang have __builtin_ctz() which returns the same result as
get_rightmost_set_bit(), and does it substantially faster. Approx
20M iterations of get_rightmost_set_bit() took ~33sec of wall clock
time on my devel machine, while 20M iterations of __builtin_ctz()
took < 9sec; get_rightmost_set_bit() is 3x slower than __builtin_ctz().
And as a side benefit, we can again eliminate the need to link libgfrpc
with libm.
Change-Id: If9e7e80874577c52223f8125b385fc930de20699
fixes: bz#1692957
Signed-off-by: Kaleb S. KEITHLEY <kkeithle@redhat.com>
| -rw-r--r-- | rpc/rpc-lib/src/rpcsvc.c | 10 |
1 files changed, 2 insertions, 8 deletions
diff --git a/rpc/rpc-lib/src/rpcsvc.c b/rpc/rpc-lib/src/rpcsvc.c index 74373c44f91..99fc92c4ea2 100644 --- a/rpc/rpc-lib/src/rpcsvc.c +++ b/rpc/rpc-lib/src/rpcsvc.c @@ -36,7 +36,6 @@ #include <fnmatch.h> #include <stdarg.h> #include <stdio.h> -#include <math.h> #include <dlfcn.h> #ifdef IPV6_DEFAULT @@ -89,12 +88,6 @@ rpcsvc_toggle_queue_status(rpcsvc_program_t *prog, return; } -static int -get_rightmost_set_bit(int n) -{ - return log2(n & -n); -} - int rpcsvc_get_free_queue_index(rpcsvc_program_t *prog) { @@ -109,7 +102,8 @@ rpcsvc_get_free_queue_index(rpcsvc_program_t *prog) right_most_unset_bit = 0; break; } else { - right_most_unset_bit = get_rightmost_set_bit( + /* get_rightmost_set_bit (sic)*/ + right_most_unset_bit = __builtin_ctz( ~prog->request_queue_status[i]); if (right_most_unset_bit < 8) { break; |