Hi Szabolcs, Thanks! Naohiro ________________________________________ From: Szabolcs Nagy Sent: Saturday, 4 September 2021 00:01 To: Tamura, Naohiro/Ìï´å Ö±ŽÚ Cc: Wilco Dijkstra; libc-alpha@sourceware.org Subject: Re: [PATCH] AArch64: Update A64FX memset not to degrade at 16KB The 08/27/2021 05:03, Naohiro Tamura via Libc-alpha wrote: > 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 thanks, i committed this now. > --- > 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 7bf759b6a753..f7dfdaace7cf 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 > -- > 2.17.1 >