linux-kernel - Re: [PATCH 0/3] riscv: optimize memcpy/memmove/memset

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Message-ID: <Zbhe6c4kCYv0uIZv@xhacker>
Date: Tue, 30 Jan 2024 10:28:57 +0800
From: Jisheng Zhang <jszhang@...nel.org>
To: Conor Dooley <conor@...nel.org>
Cc: Paul Walmsley <paul.walmsley@...ive.com>,
	Palmer Dabbelt <palmer@...belt.com>,
	Albert Ou <aou@...s.berkeley.edu>, linux-riscv@...ts.infradead.org,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH 0/3] riscv: optimize memcpy/memmove/memset

On Mon, Jan 29, 2024 at 06:16:13PM +0000, Conor Dooley wrote:
> On Sun, Jan 28, 2024 at 07:10:10PM +0800, Jisheng Zhang wrote:
> > This series is to renew Matteo's "riscv: optimized mem* functions"
> > sereies.
> > 
> > Compared with Matteo's original series, Jisheng made below changes:
> > 1. adopt Emil's change to fix boot failure when build with clang
> > 2. add corresponding changes to purgatory
> > 3. always build optimized string.c rather than only build when optimize
> > for performance
> > 4. implement unroll support when src & dst are both aligned to keep
> > the same performance as assembly version. After disassembling, I found
> > that the unroll version looks something like below, so it acchieves
> > the "unroll" effect as asm version but in C programming language:
> > 	ld	t2,0(a5)
> > 	ld	t0,8(a5)
> > 	ld	t6,16(a5)
> > 	ld	t5,24(a5)
> > 	ld	t4,32(a5)
> > 	ld	t3,40(a5)
> > 	ld	t1,48(a5)
> > 	ld	a1,56(a5)
> > 	sd	t2,0(a6)
> > 	sd	t0,8(a6)
> > 	sd	t6,16(a6)
> > 	sd	t5,24(a6)
> > 	sd	t4,32(a6)
> > 	sd	t3,40(a6)
> > 	sd	t1,48(a6)
> > 	sd	a1,56(a6)
> > And per my testing, unrolling more doesn't help performance, so
> > the "c" version only unrolls by using 8 GP regs rather than 16
> > ones as asm version.
> > 5. Add proper __pi_memcpy and __pi___memcpy alias
> > 6. more performance numbers.
> > 
> > Per my benchmark with [1] on TH1520, CV1800B and JH7110 platforms,
> > the unaligned medium memcpy performance is running about 3.5x ~ 8.6x
> > speed of the unpatched versions's! Check patch1 for more details and
> > performance numbers.
> > 
> > Link:https://github.com/ARM-software/optimized-routines/blob/master/string/bench/memcpy.c [1]
> > 
> > Here is the original cover letter msg from Matteo:
> > Replace the assembly mem{cpy,move,set} with C equivalent.
> > 
> > Try to access RAM with the largest bit width possible, but without
> > doing unaligned accesses.
> > 
> > A further improvement could be to use multiple read and writes as the
> > assembly version was trying to do.
> > 
> > Tested on a BeagleV Starlight with a SiFive U74 core, where the
> > improvement is noticeable.
> 
> However, with allmodconfig it doesn't compile:
>   Redirect to /build/tmp.zzMIlhgQQo and /build/tmp.vxnoxu8G5e
>   Tree base:
>   0c526539d432 ("riscv: optimized memcpy")
>   Building the whole tree with the patch
>   ../arch/riscv/lib/string.c:118:7: error: expected identifier or '('
>   ../arch/riscv/lib/string.c:118:7: error: expected ')'
>   ../arch/riscv/lib/string.c:143:7: error: expected identifier or '('
>   ../arch/riscv/lib/string.c:143:7: error: expected ')'
>   ../arch/riscv/lib/string.c:118:7: error: expected identifier or '('
>   ../arch/riscv/lib/string.c:118:7: error: expected ')'
>   ../arch/riscv/lib/string.c:143:7: error: expected identifier or '('
>   ../arch/riscv/lib/string.c:143:7: error: expected ')'
> 
> Seems to be the case both with llvm and gcc.

Hi Conor,

This is due to missing proper FORTIFY_SOURCE handling.
Below trival patch can fix it :)
I'm waiting for more comments before sending out v2.

diff --git a/arch/riscv/lib/string.c b/arch/riscv/lib/string.c
index 022edda68f1c..bfaab058f2cb 100644
--- a/arch/riscv/lib/string.c
+++ b/arch/riscv/lib/string.c
@@ -6,6 +6,7 @@
  * Copyright (C) 2021 Matteo Croce
  */

+#define __NO_FORTIFY
 #include <linux/types.h>
 #include <linux/module.h>
> 
> Cheers,
> Conor.
>