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From: Paul Walmsley <pjw@kernel.org>
To: Feng Jiang <jiangfeng@kylinos.cn>
Cc: pjw@kernel.org, palmer@dabbelt.com, aou@eecs.berkeley.edu,
	alex@ghiti.fr,  samuel.holland@sifive.com, charlie@rivosinc.com,
	 conor.dooley@microchip.com, linux-riscv@lists.infradead.org,
	 linux-kernel@vger.kernel.org
Subject: Re: [PATCH] riscv: lib: optimize strlen loop efficiency
Date: Wed, 14 Jan 2026 19:03:17 -0700 (MST)	[thread overview]
Message-ID: <d356705a-843c-06dc-38a3-77eae7d2ef59@kernel.org> (raw)
In-Reply-To: <20251218032614.57356-1-jiangfeng@kylinos.cn>

On Thu, 18 Dec 2025, Feng Jiang wrote:

> Optimize the generic strlen implementation by using a pre-decrement
> pointer. This reduces the loop body from 4 instructions to 3 and
> eliminates the unconditional jump ('j').
> 
> Old loop (4 instructions, 2 branches):
>   1: lbu t0, 0(t1); beqz t0, 2f; addi t1, t1, 1; j 1b
> 
> New loop (3 instructions, 1 branch):
>   1: addi t1, t1, 1; lbu t0, 0(t1); bnez t0, 1b
> 
> This change improves execution efficiency and reduces branch pressure
> for systems without the Zbb extension.

Looks reasonable; do you have any benchmarks on hardware that you can 
share?  Any reason why this patch stands alone and isn't rolled up as part 
of your "optimize string function" series?


- Paul

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  reply	other threads:[~2026-01-15  2:03 UTC|newest]

Thread overview: 10+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2025-12-18  3:26 [PATCH] riscv: lib: optimize strlen loop efficiency Feng Jiang
2026-01-15  2:03 ` Paul Walmsley [this message]
2026-01-15  3:23   ` Feng Jiang
2026-01-24  8:14     ` Paul Walmsley
2026-01-26  3:05       ` Feng Jiang
2026-01-15 11:19   ` David Laight
2026-01-15 18:46     ` David Laight
2026-01-26  2:52       ` Feng Jiang
2026-01-28 18:59       ` David Laight
2026-01-29  8:34         ` Feng Jiang

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