This is the mail archive of the
glibc-bugs@sourceware.org
mailing list for the glibc project.
[Bug math/13932] New: x86_64 pow unexpectedly slow for some inputs
- From: "ppluzhnikov at google dot com" <sourceware-bugzilla at sourceware dot org>
- To: glibc-bugs at sources dot redhat dot com
- Date: Fri, 30 Mar 2012 21:28:42 +0000
- Subject: [Bug math/13932] New: x86_64 pow unexpectedly slow for some inputs
- Auto-submitted: auto-generated
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
--
Configure bugmail: http://sourceware.org/bugzilla/userprefs.cgi?tab=email
------- You are receiving this mail because: -------
You are on the CC list for the bug.