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* [Bug math/13932] New: x86_64 pow unexpectedly slow for some inputs
@ 2012-03-31  2:23 ppluzhnikov at google dot com
  2012-12-13 16:45 ` [Bug math/13932] " manu at gcc dot gnu.org
                   ` (18 more replies)
  0 siblings, 19 replies; 20+ messages in thread
From: ppluzhnikov at google dot com @ 2012-03-31  2:23 UTC (permalink / raw)
  To: glibc-bugs

http://sourceware.org/bugzilla/show_bug.cgi?id=13932

             Bug #: 13932
           Summary: x86_64 pow unexpectedly slow for some inputs
           Product: glibc
           Version: unspecified
            Status: NEW
          Severity: normal
          Priority: P2
         Component: math
        AssignedTo: unassigned@sourceware.org
        ReportedBy: ppluzhnikov@google.com
    Classification: Unclassified


Created attachment 6310
  --> http://sourceware.org/bugzilla/attachment.cgi?id=6310
test case

Attached test case shows that pow is over 10,000 slower for some inputs
than for other (nearby) inputs.

This was first noticed with eglibc-2.11, and reproduced with current
git trunk.

Results:

32-bit build:

./elf/ld.so --library-path .:math:dlfcn ./a.out
pow(0.562500, 1.5): 13.644814 calls/usec
pow(0.563250, 1.5): 13.647048 calls/usec
ratio:      1

64-bit build:

./elf/ld.so --library-path .:math:dlfcn ./a.out
pow(0.562500, 1.5): 0.000982 calls/usec
pow(0.563250, 1.5): 13.574397 calls/usec
ratio:  13828


perf shows:

# Events: 15K cycles
#
# Overhead  Command      Shared Object                               Symbol
# ........  .......  .................  ...................................
#
    63.31%    ld.so  libm.so            [.] __mul
    18.44%    ld.so  libm.so            [.] __ieee754_pow_sse2
    13.81%    ld.so  libm.so            [.] __exp1
     1.20%    ld.so  libm.so            [.] __pow
     1.09%    ld.so  libm.so            [.] sub_magnitudes
     0.43%    ld.so  a.out              [.] main
     0.38%    ld.so  libm.so            [.] __cpy
     0.21%    ld.so  libm.so            [.] add_magnitudes
     0.19%    ld.so  libm.so            [.] @plt

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^ permalink raw reply	[flat|nested] 20+ messages in thread
end of thread, other threads:[~2020-05-25 13:19 UTC | newest]

Thread overview: 20+ messages (download: mbox.gz / follow: Atom feed)
-- links below jump to the message on this page --
2012-03-31  2:23 [Bug math/13932] New: x86_64 pow unexpectedly slow for some inputs ppluzhnikov at google dot com
2012-12-13 16:45 ` [Bug math/13932] " manu at gcc dot gnu.org
2012-12-13 18:58 ` ppluzhnikov at google dot com
2013-01-04 11:33 ` siddhesh at redhat dot com
2013-01-04 23:24 ` herve at guillemet dot org
2013-03-08 14:08 ` manu at gcc dot gnu.org
2013-03-11  6:29 ` siddhesh at redhat dot com
2013-03-11  6:36 ` siddhesh at redhat dot com
2013-03-11  9:07 ` manu at gcc dot gnu.org
2013-03-11 10:19 ` siddhesh at redhat dot com
2013-08-24 21:39 ` vz-sourceware at zeitlins dot org
2013-12-03 18:42 ` jsm28 at gcc dot gnu.org
2014-02-06 18:27 ` [Bug math/13932] dbl-64 " jsm28 at gcc dot gnu.org
2014-05-07 15:42 ` jsm28 at gcc dot gnu.org
2014-06-12 19:26 ` fweimer at redhat dot com
2020-05-23 19:32 ` mtk.manpages at gmail dot com
2020-05-23 21:31 ` vincent-srcware at vinc17 dot net
2020-05-25 11:38 ` mtk.manpages at gmail dot com
2020-05-25 12:08 ` vincent-srcware at vinc17 dot net
2020-05-25 13:19 ` mtk.manpages at gmail dot com

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