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* [glibc/maskray/unnest] AArch64: Update A64FX memset not to degrade at 16KB
@ 2021-09-23 0:43 Fangrui Song
0 siblings, 0 replies; 2+ messages in thread
From: Fangrui Song @ 2021-09-23 0:43 UTC (permalink / raw)
To: glibc-cvs
https://sourceware.org/git/gitweb.cgi?p=glibc.git;h=1d9f99ce1b3788d1897cb53a76d57e973111b8fe
commit 1d9f99ce1b3788d1897cb53a76d57e973111b8fe
Author: Naohiro Tamura <naohirot@fujitsu.com>
Date: Fri Aug 27 05:03:04 2021 +0000
AArch64: Update A64FX memset not to degrade at 16KB
This patch updates unroll8 code so as not to degrade at the peak
performance 16KB for both FX1000 and FX700.
Inserted 2 instructions at the beginning of the unroll8 loop,
cmp and branch, are a workaround that is found heuristically.
Reviewed-by: Wilco Dijkstra <Wilco.Dijkstra@arm.com>
Diff:
---
sysdeps/aarch64/multiarch/memset_a64fx.S | 9 ++++++++-
1 file changed, 8 insertions(+), 1 deletion(-)
diff --git a/sysdeps/aarch64/multiarch/memset_a64fx.S b/sysdeps/aarch64/multiarch/memset_a64fx.S
index 7bf759b6a7..f7dfdaace7 100644
--- a/sysdeps/aarch64/multiarch/memset_a64fx.S
+++ b/sysdeps/aarch64/multiarch/memset_a64fx.S
@@ -96,7 +96,14 @@ L(vl_agnostic): // VL Agnostic
L(unroll8):
sub count, count, tmp1
.p2align 4
-1: st1b_unroll 0, 7
+ // The 2 instructions at the beginning of the following loop,
+ // cmp and branch, are a workaround so as not to degrade at
+ // the peak performance 16KB.
+ // It is found heuristically and the branch condition, b.ne,
+ // is chosen intentionally never to jump.
+1: cmp xzr, xzr
+ b.ne 1b
+ st1b_unroll 0, 7
add dst, dst, tmp1
subs count, count, tmp1
b.hi 1b
^ permalink raw reply [flat|nested] 2+ messages in thread
* [glibc/maskray/unnest] AArch64: Update A64FX memset not to degrade at 16KB
@ 2021-09-03 17:05 Fangrui Song
0 siblings, 0 replies; 2+ messages in thread
From: Fangrui Song @ 2021-09-03 17:05 UTC (permalink / raw)
To: glibc-cvs
https://sourceware.org/git/gitweb.cgi?p=glibc.git;h=23777232c23f80809613bdfa329f63aadf992922
commit 23777232c23f80809613bdfa329f63aadf992922
Author: Naohiro Tamura via Libc-alpha <libc-alpha@sourceware.org>
Date: Fri Aug 27 05:03:04 2021 +0000
AArch64: Update A64FX memset not to degrade at 16KB
This patch updates unroll8 code so as not to degrade at the peak
performance 16KB for both FX1000 and FX700.
Inserted 2 instructions at the beginning of the unroll8 loop,
cmp and branch, are a workaround that is found heuristically.
Reviewed-by: Wilco Dijkstra <Wilco.Dijkstra@arm.com>
Diff:
---
sysdeps/aarch64/multiarch/memset_a64fx.S | 9 ++++++++-
1 file changed, 8 insertions(+), 1 deletion(-)
diff --git a/sysdeps/aarch64/multiarch/memset_a64fx.S b/sysdeps/aarch64/multiarch/memset_a64fx.S
index 7bf759b6a7..f7dfdaace7 100644
--- a/sysdeps/aarch64/multiarch/memset_a64fx.S
+++ b/sysdeps/aarch64/multiarch/memset_a64fx.S
@@ -96,7 +96,14 @@ L(vl_agnostic): // VL Agnostic
L(unroll8):
sub count, count, tmp1
.p2align 4
-1: st1b_unroll 0, 7
+ // The 2 instructions at the beginning of the following loop,
+ // cmp and branch, are a workaround so as not to degrade at
+ // the peak performance 16KB.
+ // It is found heuristically and the branch condition, b.ne,
+ // is chosen intentionally never to jump.
+1: cmp xzr, xzr
+ b.ne 1b
+ st1b_unroll 0, 7
add dst, dst, tmp1
subs count, count, tmp1
b.hi 1b
^ permalink raw reply [flat|nested] 2+ messages in thread
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