linux-kernel - Re: [PATCH 1/1] riscv: __asm_copy_to-from_user: Improve using word copy if size

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Date:   Sun, 15 Aug 2021 08:51:18 +0200
From:   Andreas Schwab <schwab@...ux-m68k.org>
To:     Akira Tsukamoto <akira.tsukamoto@...il.com>
Cc:     Paul Walmsley <paul.walmsley@...ive.com>,
        Palmer Dabbelt <palmer@...belt.com>,
        Guenter Roeck <linux@...ck-us.net>,
        Geert Uytterhoeven <geert@...ux-m68k.org>,
        Qiu Wenbo <qiuwenbo@...inos.com.cn>,
        Albert Ou <aou@...s.berkeley.edu>,
        linux-riscv@...ts.infradead.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 1/1] riscv: __asm_copy_to-from_user: Improve using word
 copy if size < 9*SZREG

On Jul 30 2021, Akira Tsukamoto wrote:

>  .Lword_copy:
> -        /*
> -	 * Both src and dst are aligned, unrolled word copy
> +	/*
> +	 * Both src and dst are aligned
> +	 * None unrolled word copy with every 1*SZREG iteration
> +	 *
> +	 * a0 - start of aligned dst
> +	 * a1 - start of aligned src
> +	 * t0 - end of aligned dst
> +	 */
> +	bgeu	a0, t0, .Lbyte_copy_tail /* check if end of copy */
> +	addi	t0, t0, -(SZREG) /* not to over run */
> +1:
> +	REG_L	a5, 0(a1)
> +	addi	a1, a1, SZREG
> +	REG_S	a5, 0(a0)
> +	addi	a0, a0, SZREG
> +	bltu	a0, t0, 1b

This is missing fixups.

Andreas.

-- 
Andreas Schwab, schwab@...ux-m68k.org
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