A performance regression was introduced by commit
84d74e427a "powerpc: Cleanup fenv_private.h".
In the powerpc implementation of SET_RESTORE_ROUND, there is the
following code in the "SET" function (slightly simplified):
--
old.fenv = fegetenv_register ();
new.l = (old.l & _FPU_MASK_TRAPS_RN) | r; (1)
if (new.l != old.l) (2)
{
if ((old.l & _FPU_ALL_TRAPS) != 0)
(void) __fe_mask_env ();
fesetenv_register (new.fenv); (3)
--
Line (1) sets the value of "new" to the current value of FPSCR,
but masks off summary bits, exceptions, non-IEEE mode, and
rounding mode, then ORs in the new rounding mode.
Line (2) compares this new value to the current value in order to
avoid setting a new value in the FPSCR (line (3)) unless something
significant has changed (exception enables or rounding mode).
The summary bits are not germane to the comparison, but are cleared
in "new" and preserved in "old", resulting in false negative
comparisons, and unnecessarily setting the FPSCR in those cases
with associated negative performance impacts.
The solution is to treat the summaries identically for "new" and "old":
- save them in SET
- leave them alone otherwise
- restore the saved values in RESTORE
Also minor changes:
- expand _FPU_MASK_RN to 64bit hex, to match other MASKs
- treat bit 52 (left-to-right) as reserved (since it is)
* sysdeps/powerpc/fpu/fenv_private.h (_FPU_MASK_TRAPS_RN):
(_FPU_MASK_FRAC_INEX_RET_CC): Fix masks to more properly handle
summary bits.
(_FPU_MASK_RN): Expand _FPU_MASK_RN to 64bit hex.
(_FPU_MASK_NOT_RN_NI): Treat bit 52 (left-to-right) as reserved.
Reviewed-by: Tulio Magno Quites Machado Filho <tuliom@linux.vnet.ibm.com>
Some of the masks are wrong, and the naming is confusing.
There are two basic cases we really care about:
1. Stacking a new rounding mode when running certain
sections of code, and pausing exception handling.
2. Likewise, but discarding any exceptions which occur
while running under the new rounding mode.
libc_feholdexcept_setround_ppc_ctx has been removed as it basically
does the same thing as libc_feholdsetround_ppc_ctx but also clearing
any sticky bits. The restore behavior is what differentiates these
two cases as the SET_RESTORE_ROUND{,_NOEX} macros will either merge
or discard all exceptions occurring during scope of their usage.
Likewise, there are a number of routines to swap, replace,
or merge FP environments. This change reduces much of
the common and sometimes wrong code.
Tested on ppc64le, with results before and after.
The ldbl-128ibm implementation of nearbyintl uses logic that only
works in round-to-nearest mode. This contrasts with rintl, which
works in all rounding modes.
Now, arguably nearbyintl could simply be aliased to rintl, given that
spurious "inexact" is generally allowed for ldbl-128ibm, even for the
underlying arithmetic operations. But given that the only point of
nearbyintl is to avoid "inexact", this patch follows the more
conservative approach of adding conditionals to the rintl
implementation to make it suitable for use to implement nearbyintl,
then builds it for nearbyintl with USE_AS_NEARBYINTL defined. The
test test-nearbyint-except-2 shows up issues when traps on "inexact"
are enabled, which turn out to be problems with the powerpc
fenv_private.h implementation (two functions that should disable
exception traps potentially failing to do so in some cases); this
patch duly fixes that as well (I don't see any other existing cases
where this would be user-visible; there isn't much use of *_NOEX,
*hold* etc. in libm that requires exceptions to be discarded and not
trapped on).
Tested for powerpc.
[BZ #19790]
* sysdeps/ieee754/ldbl-128ibm/s_rintl.c [USE_AS_NEARBYINTL]
(rintl): Define as macro.
[USE_AS_NEARBYINTL] (__rintl): Likewise.
(__rintl) [USE_AS_NEARBYINTL]: Use SET_RESTORE_ROUND_NOEX instead
of fesetround. Ensure results are evaluated before end of scope.
* sysdeps/ieee754/ldbl-128ibm/s_nearbyintl.c: Define
USE_AS_NEARBYINTL and include s_rintl.c.
* sysdeps/powerpc/fpu/fenv_private.h (libc_feholdsetround_ppc):
Disable exception traps in new environment.
(libc_feholdsetround_ppc_ctx): Likewise.
Continuing the fixes for C90 libm functions calling C99 fe* functions,
this patch fixes the case of fesetround by making it a weak alias of
__fesetround and making the affected code call __fesetround. An
existing __fesetround function in fenv_libc.h for powerpc is renamed
to __fesetround_inline.
Tested for x86_64 (testsuite, and that disassembly of installed shared
libraries is unchanged by the patch). Also tested for ARM
(soft-float) that fesetround failures disappear from the linknamespace
test results (feupdateenv remains to be addressed to complete fixing
bug 17748).
[BZ #17748]
* include/fenv.h (__fesetround): Declare. Use libm_hidden_proto.
* math/fesetround.c (fesetround): Rename to __fesetround and
define as weak alias of __fesetround. Use libm_hidden_weak.
* sysdeps/aarch64/fpu/fesetround.c (fesetround): Likewise.
* sysdeps/alpha/fpu/fesetround.c (fesetround): Likewise.
* sysdeps/arm/fesetround.c (fesetround): Likewise.
* sysdeps/hppa/fpu/fesetround.c (fesetround): Likewise.
* sysdeps/i386/fpu/fesetround.c (fesetround): Likewise.
* sysdeps/ia64/fpu/fesetround.c (fesetround): Likewise.
* sysdeps/m68k/fpu/fesetround.c (fesetround): Likewise.
* sysdeps/mips/fpu/fesetround.c (fesetround): Likewise.
* sysdeps/powerpc/fpu/fenv_libc.h (__fesetround): Rename to
__fesetround_inline.
* sysdeps/powerpc/fpu/fenv_private.h (libc_fesetround_ppc): Call
__fesetround_inline instead of __fesetround.
* sysdeps/powerpc/fpu/fesetround.c (fesetround): Rename to
__fesetround and define as weak alias of __fesetround. Use
libm_hidden_weak. Call __fesetround_inline instead of
__fesetround.
* sysdeps/powerpc/nofpu/fesetround.c (fesetround): Rename to
__fesetround and define as weak alias of __fesetround. Use
libm_hidden_weak.
* sysdeps/powerpc/powerpc32/e500/nofpu/fesetround.c (fesetround):
Likewise.
* sysdeps/s390/fpu/fesetround.c (fesetround): Likewise.
* sysdeps/sh/sh4/fpu/fesetround.c (fesetround): Likewise.
* sysdeps/sparc/fpu/fesetround.c (fesetround): Likewise.
* sysdeps/tile/math_private.h (__fesetround): New inline function.
* sysdeps/x86_64/fpu/fesetround.c (fesetround): Rename to
__fesetround and define as weak alias of __fesetround. Use
libm_hidden_weak.
* sysdeps/generic/math_private.h (default_libc_fesetround): Call
__fesetround instead of fesetround.
(default_libc_feholdexcept_setround): Likewise.
(libc_feholdsetround_ctx): Likewise.
(libc_feholdsetround_noex_ctx): Likewise.
This patch helps some math functions performance by adding the libc_fexxx
variant of inline functions to handle both FPU round and exception set/restore
and by using them on the libc_fexxx_ctx functions. It is based on already coded
fexxx family functions for PPC with fpu.
Here is the summary of performance improvements due this patch (measured on a
POWER7 machine):
Before:
cos(): ITERS:9.5895e+07: TOTAL:5116.03Mcy, MAX:77.6cy, MIN:49.792cy, 18744 calls/Mcy
exp(): ITERS:2.827e+07: TOTAL:5187.15Mcy, MAX:494.018cy, MIN:38.422cy, 5450.01 calls/Mcy
pow(): ITERS:6.1705e+07: TOTAL:5144.26Mcy, MAX:171.95cy, MIN:29.935cy, 11994.9 calls/Mcy
sin(): ITERS:8.6898e+07: TOTAL:5117.06Mcy, MAX:83.841cy, MIN:46.582cy, 16982 calls/Mcy
tan(): ITERS:2.9473e+07: TOTAL:5115.39Mcy, MAX:191.017cy, MIN:172.352cy, 5761.63 calls/Mcy
After:
cos(): ITERS:2.05265e+08: TOTAL:5111.37Mcy, MAX:78.754cy, MIN:24.196cy, 40158.5 calls/Mcy
exp(): ITERS:3.341e+07: TOTAL:5170.84Mcy, MAX:476.317cy, MIN:15.574cy, 6461.23 calls/Mcy
pow(): ITERS:7.6153e+07: TOTAL:5129.1Mcy, MAX:147.5cy, MIN:30.916cy, 14847.2 calls/Mcy
sin(): ITERS:1.58816e+08: TOTAL:5115.11Mcy, MAX:1490.39cy, MIN:22.341cy, 31048.4 calls/Mcy
tan(): ITERS:3.4964e+07: TOTAL:5114.18Mcy, MAX:177.422cy, MIN:146.115cy, 6836.68 calls/Mcy
