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

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Date: Mon, 29 Jan 2024 18:16:13 +0000
From: Conor Dooley <conor@...nel.org>
To: Jisheng Zhang <jszhang@...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 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.

Cheers,
Conor.


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