linux-kernel - Re: [PATCH] riscv: lib: optimize strlen loop efficiency

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Message-ID: <d356705a-843c-06dc-38a3-77eae7d2ef59@kernel.org>
Date: Wed, 14 Jan 2026 19:03:17 -0700 (MST)
From: Paul Walmsley <pjw@...nel.org>
To: Feng Jiang <jiangfeng@...inos.cn>
cc: pjw@...nel.org, palmer@...belt.com, aou@...s.berkeley.edu, alex@...ti.fr, 
    samuel.holland@...ive.com, charlie@...osinc.com, 
    conor.dooley@...rochip.com, linux-riscv@...ts.infradead.org, 
    linux-kernel@...r.kernel.org
Subject: Re: [PATCH] riscv: lib: optimize strlen loop efficiency

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