This is a note to let you know that I've just added the patch titled
MIPS: Avoid DIVU in `__div64_32' is result would be zero
to the 5.11-stable tree which can be found at:
http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary
The filename of the patch is:
mips-avoid-divu-in-__div64_32-is-result-would-be-zero.patch
and it can be found in the queue-5.11 subdirectory.
If you, or anyone else, feels it should not be added to the stable tree,
please let <stable@xxxxxxxxxxxxxxx> know about it.
>From c1d337d45ec0a802299688e17d568c4e3a585895 Mon Sep 17 00:00:00 2001
From: "Maciej W. Rozycki" <macro@xxxxxxxxxxx>
Date: Tue, 20 Apr 2021 04:50:48 +0200
Subject: MIPS: Avoid DIVU in `__div64_32' is result would be zero
From: Maciej W. Rozycki <macro@xxxxxxxxxxx>
commit c1d337d45ec0a802299688e17d568c4e3a585895 upstream.
We already check the high part of the divident against zero to avoid the
costly DIVU instruction in that case, needed to reduce the high part of
the divident, so we may well check against the divisor instead and set
the high part of the quotient to zero right away. We need to treat the
high part the divident in that case though as the remainder that would
be calculated by the DIVU instruction we avoided.
This has passed correctness verification with test_div64 and reduced the
module's average execution time down to 1.0445s and 0.2619s from 1.0668s
and 0.2629s respectively for an R3400 CPU @40MHz and a 5Kc CPU @160MHz.
Signed-off-by: Maciej W. Rozycki <macro@xxxxxxxxxxx>
Signed-off-by: Thomas Bogendoerfer <tsbogend@xxxxxxxxxxxxxxxx>
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>
---
arch/mips/include/asm/div64.h | 6 ++++--
1 file changed, 4 insertions(+), 2 deletions(-)
--- a/arch/mips/include/asm/div64.h
+++ b/arch/mips/include/asm/div64.h
@@ -68,9 +68,11 @@
\
__high = __div >> 32; \
__low = __div; \
- __upper = __high; \
\
- if (__high) { \
+ if (__high < __radix) { \
+ __upper = __high; \
+ __high = 0; \
+ } else { \
__asm__("divu $0, %z1, %z2" \
: "=x" (__modquot) \
: "Jr" (__high), "Jr" (__radix)); \
Patches currently in stable-queue which might be from macro@xxxxxxxxxxx are
queue-5.11/mips-reinstate-platform-__div64_32-handler.patch
queue-5.11/mips-avoid-handcoded-divu-in-__div64_32-altogether.patch
queue-5.11/mips-avoid-divu-in-__div64_32-is-result-would-be-zero.patch
