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* [Bug manual/15267] New: Add note on performance characteristics of some libm functions
@ 2013-03-11 6:35 siddhesh at redhat dot com
2013-03-11 9:10 ` [Bug manual/15267] " manu at gcc dot gnu.org
` (7 more replies)
0 siblings, 8 replies; 9+ messages in thread
From: siddhesh at redhat dot com @ 2013-03-11 6:35 UTC (permalink / raw)
To: glibc-bugs
http://sourceware.org/bugzilla/show_bug.cgi?id=15267
Bug #: 15267
Summary: Add note on performance characteristics of some libm
functions
Product: glibc
Version: unspecified
Status: NEW
Severity: normal
Priority: P2
Component: manual
AssignedTo: unassigned@sourceware.org
ReportedBy: siddhesh@redhat.com
CC: mtk.manpages@gmail.com, roland@gnu.org
Classification: Unclassified
libm has a fallback to multiprecision calculation for some functions (log, exp,
atan, pow, etc.) which is much slower than the fast path. While the inputs
that trigger this are unknown, it would be useful to document the fact that
there is such a performance difference, along with an explanation of why the
multiprecision stage is needed at all.
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* [Bug manual/15267] Add note on performance characteristics of some libm functions
2013-03-11 6:35 [Bug manual/15267] New: Add note on performance characteristics of some libm functions siddhesh at redhat dot com
@ 2013-03-11 9:10 ` manu at gcc dot gnu.org
2013-03-15 5:57 ` bugdal at aerifal dot cx
` (6 subsequent siblings)
7 siblings, 0 replies; 9+ messages in thread
From: manu at gcc dot gnu.org @ 2013-03-11 9:10 UTC (permalink / raw)
To: glibc-bugs
http://sourceware.org/bugzilla/show_bug.cgi?id=15267
Manuel López-Ibáñez <manu at gcc dot gnu.org> changed:
What |Removed |Added
----------------------------------------------------------------------------
CC| |manu at gcc dot gnu.org
--- Comment #1 from Manuel López-Ibáñez <manu at gcc dot gnu.org> 2013-03-11 09:10:09 UTC ---
Some background on why such documentation could save a lot of frustration can
be found in bug 13932, and in http://entropymine.com/imageworsener/slowpow/,
and simply by googling "slowpow".
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* [Bug manual/15267] Add note on performance characteristics of some libm functions
2013-03-11 6:35 [Bug manual/15267] New: Add note on performance characteristics of some libm functions siddhesh at redhat dot com
2013-03-11 9:10 ` [Bug manual/15267] " manu at gcc dot gnu.org
@ 2013-03-15 5:57 ` bugdal at aerifal dot cx
2013-03-15 14:38 ` carlos at redhat dot com
` (5 subsequent siblings)
7 siblings, 0 replies; 9+ messages in thread
From: bugdal at aerifal dot cx @ 2013-03-15 5:57 UTC (permalink / raw)
To: glibc-bugs
http://sourceware.org/bugzilla/show_bug.cgi?id=15267
Rich Felker <bugdal at aerifal dot cx> changed:
What |Removed |Added
----------------------------------------------------------------------------
CC| |bugdal at aerifal dot cx
--- Comment #2 from Rich Felker <bugdal at aerifal dot cx> 2013-03-15 05:57:21 UTC ---
Shouldn't this issue just be fixed? IEEE specifically omits the requirement of
correct rounding for transcendental functions because of the long-known issue
that there's no known efficient way to compute the correctly-rounded results.
As far as I can tell, no other libm implementations have these performance
bugs; they're unique to glibc and the "IBM Accurate Mathematical Library"
written for glibc.
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* [Bug manual/15267] Add note on performance characteristics of some libm functions
2013-03-11 6:35 [Bug manual/15267] New: Add note on performance characteristics of some libm functions siddhesh at redhat dot com
2013-03-11 9:10 ` [Bug manual/15267] " manu at gcc dot gnu.org
2013-03-15 5:57 ` bugdal at aerifal dot cx
@ 2013-03-15 14:38 ` carlos at redhat dot com
2014-06-13 18:42 ` fweimer at redhat dot com
` (4 subsequent siblings)
7 siblings, 0 replies; 9+ messages in thread
From: carlos at redhat dot com @ 2013-03-15 14:38 UTC (permalink / raw)
To: glibc-bugs
http://sourceware.org/bugzilla/show_bug.cgi?id=15267
Carlos O'Donell <carlos at redhat dot com> changed:
What |Removed |Added
----------------------------------------------------------------------------
CC| |carlos at redhat dot com
--- Comment #3 from Carlos O'Donell <carlos at redhat dot com> 2013-03-15 14:37:59 UTC ---
(In reply to comment #2)
> Shouldn't this issue just be fixed? IEEE specifically omits the requirement of
> correct rounding for transcendental functions because of the long-known issue
> that there's no known efficient way to compute the correctly-rounded results.
> As far as I can tell, no other libm implementations have these performance
> bugs; they're unique to glibc and the "IBM Accurate Mathematical Library"
> written for glibc.
Sorry, are you advocating we "fix it" as opposed to "document it?"
If you are then I agree, but documenting things until you fix them is a good
intermediate step.
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* [Bug manual/15267] Add note on performance characteristics of some libm functions
2013-03-11 6:35 [Bug manual/15267] New: Add note on performance characteristics of some libm functions siddhesh at redhat dot com
` (2 preceding siblings ...)
2013-03-15 14:38 ` carlos at redhat dot com
@ 2014-06-13 18:42 ` fweimer at redhat dot com
2014-06-13 18:43 ` fweimer at redhat dot com
` (3 subsequent siblings)
7 siblings, 0 replies; 9+ messages in thread
From: fweimer at redhat dot com @ 2014-06-13 18:42 UTC (permalink / raw)
To: glibc-bugs
https://sourceware.org/bugzilla/show_bug.cgi?id=15267
Florian Weimer <fweimer at redhat dot com> changed:
What |Removed |Added
----------------------------------------------------------------------------
CC| |fweimer at redhat dot com
Flags| |security-
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* [Bug manual/15267] Add note on performance characteristics of some libm functions
2013-03-11 6:35 [Bug manual/15267] New: Add note on performance characteristics of some libm functions siddhesh at redhat dot com
` (3 preceding siblings ...)
2014-06-13 18:42 ` fweimer at redhat dot com
@ 2014-06-13 18:43 ` fweimer at redhat dot com
2020-05-19 13:53 ` [Bug manual/15267] Fix libm performance by relaxing ULP errors carlos at redhat dot com
` (2 subsequent siblings)
7 siblings, 0 replies; 9+ messages in thread
From: fweimer at redhat dot com @ 2014-06-13 18:43 UTC (permalink / raw)
To: glibc-bugs
https://sourceware.org/bugzilla/show_bug.cgi?id=15267
Florian Weimer <fweimer at redhat dot com> changed:
What |Removed |Added
----------------------------------------------------------------------------
CC|fweimer at redhat dot com |
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* [Bug manual/15267] Fix libm performance by relaxing ULP errors.
2013-03-11 6:35 [Bug manual/15267] New: Add note on performance characteristics of some libm functions siddhesh at redhat dot com
` (4 preceding siblings ...)
2014-06-13 18:43 ` fweimer at redhat dot com
@ 2020-05-19 13:53 ` carlos at redhat dot com
2020-05-19 13:53 ` carlos at redhat dot com
2021-03-11 14:46 ` wdijkstr at arm dot com
7 siblings, 0 replies; 9+ messages in thread
From: carlos at redhat dot com @ 2020-05-19 13:53 UTC (permalink / raw)
To: glibc-bugs
https://sourceware.org/bugzilla/show_bug.cgi?id=15267
Carlos O'Donell <carlos at redhat dot com> changed:
What |Removed |Added
----------------------------------------------------------------------------
Summary|Add note on performance |Fix libm performance by
|characteristics of some |relaxing ULP errors.
|libm functions |
--- Comment #5 from Carlos O'Donell <carlos at redhat dot com> ---
I'm going to retitle this bug and instead of saying we're going to document the
performance issues, we should fix them.
We have already agreed to relax the ULPs to 9 ULPs for all functions and thus
remove the MP-fallback paths in these cases.
We have just had a user report that:
* acos
* asin
Both have MP-fallback cases that are very bad and should be fixed.
Szabolcs Nagy from Arm has worked on many of these fixes.
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* [Bug manual/15267] Fix libm performance by relaxing ULP errors.
2013-03-11 6:35 [Bug manual/15267] New: Add note on performance characteristics of some libm functions siddhesh at redhat dot com
` (5 preceding siblings ...)
2020-05-19 13:53 ` [Bug manual/15267] Fix libm performance by relaxing ULP errors carlos at redhat dot com
@ 2020-05-19 13:53 ` carlos at redhat dot com
2021-03-11 14:46 ` wdijkstr at arm dot com
7 siblings, 0 replies; 9+ messages in thread
From: carlos at redhat dot com @ 2020-05-19 13:53 UTC (permalink / raw)
To: glibc-bugs
https://sourceware.org/bugzilla/show_bug.cgi?id=15267
Carlos O'Donell <carlos at redhat dot com> changed:
What |Removed |Added
----------------------------------------------------------------------------
CC| |nszabolcs at gmail dot com
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* [Bug manual/15267] Fix libm performance by relaxing ULP errors.
2013-03-11 6:35 [Bug manual/15267] New: Add note on performance characteristics of some libm functions siddhesh at redhat dot com
` (6 preceding siblings ...)
2020-05-19 13:53 ` carlos at redhat dot com
@ 2021-03-11 14:46 ` wdijkstr at arm dot com
7 siblings, 0 replies; 9+ messages in thread
From: wdijkstr at arm dot com @ 2021-03-11 14:46 UTC (permalink / raw)
To: glibc-bugs
https://sourceware.org/bugzilla/show_bug.cgi?id=15267
Wilco <wdijkstr at arm dot com> changed:
What |Removed |Added
----------------------------------------------------------------------------
CC| |wdijkstr at arm dot com
--- Comment #6 from Wilco <wdijkstr at arm dot com> ---
All slow paths have now been removed from all math functions.
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2013-03-11 6:35 [Bug manual/15267] New: Add note on performance characteristics of some libm functions siddhesh at redhat dot com
2013-03-11 9:10 ` [Bug manual/15267] " manu at gcc dot gnu.org
2013-03-15 5:57 ` bugdal at aerifal dot cx
2013-03-15 14:38 ` carlos at redhat dot com
2014-06-13 18:42 ` fweimer at redhat dot com
2014-06-13 18:43 ` fweimer at redhat dot com
2020-05-19 13:53 ` [Bug manual/15267] Fix libm performance by relaxing ULP errors carlos at redhat dot com
2020-05-19 13:53 ` carlos at redhat dot com
2021-03-11 14:46 ` wdijkstr at arm dot com
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