From 1d9f99ce1b3788d1897cb53a76d57e973111b8fe Mon Sep 17 00:00:00 2001 From: Naohiro Tamura Date: Fri, 27 Aug 2021 05:03:04 +0000 Subject: [PATCH] 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 --- 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 -- 2.31.1