From: Nam Cao <namcao@linutronix.de>
To: Jisheng Zhang <jszhang@kernel.org>
Cc: Paul Walmsley <pjw@kernel.org>,
Palmer Dabbelt <palmer@dabbelt.com>,
Albert Ou <aou@eecs.berkeley.edu>,
Alexandre Ghiti <alex@ghiti.fr>,
linux-riscv@lists.infradead.org, linux-kernel@vger.kernel.org
Subject: Re: [PATCH 1/3] riscv: word-at-a-time: improve find_zero() for !RISCV_ISA_ZBB
Date: Thu, 03 Sep 2026 11:35:25 +0200 [thread overview]
Message-ID: <87a4py65k2.fsf@yellow.woof> (raw)
In-Reply-To: <apZVwzxBD8Ih493W@xhacker>
Jisheng Zhang <jszhang@kernel.org> writes:
> On Thu, Aug 20, 2026 at 10:31:49AM +0200, Nam Cao wrote:
>> Jisheng Zhang <jszhang@kernel.org> writes:
>> > +#if !(defined(CONFIG_RISCV_ISA_ZBB) && defined(CONFIG_TOOLCHAIN_HAS_ZBB))
>> > +#include <asm-generic/word-at-a-time.h>
>> > +#else
>>
>> Instead of this #if, would it be better to do
>>
>> static inline unsigned long find_zero(unsigned long mask)
>> {
>> if (IS_ENABLED(CONFIG_RISCV_ISA_ZBB) && IS_ENABLED(CONFIG_TOOLCHAIN_HAS_ZBB) &&
>> riscv_has_extension_likely(RISCV_ISA_EXT_ZBB))
>> return !mask ? 0 : ((__fls(mask) + 1) >> 3);
>>
>> return count_masked_bytes(mask);
>> }
>>
>> and let compiler's dead code elimination does its job?
>
> This is impossible because the generic word-at-a-time.h implements
> the generic find_zero() itself, so there will be compile error.
Don't include word-at-a-time.h then? It compiles fine for me (obviously
count_masked_bytes() from PATCH 2/3 needs to be added first).
Nam
next prev parent reply other threads:[~2026-09-03 9:35 UTC|newest]
Thread overview: 8+ messages / expand[flat|nested] mbox.gz Atom feed top
2026-01-13 12:24 [PATCH 0/3] riscv: word-at-a-time: improve find_zero() Jisheng Zhang
2026-01-13 12:24 ` [PATCH 1/3] riscv: word-at-a-time: improve find_zero() for !RISCV_ISA_ZBB Jisheng Zhang
2026-08-20 8:31 ` Nam Cao
2026-09-01 4:34 ` Jisheng Zhang
2026-09-03 9:35 ` Nam Cao [this message]
2026-01-13 12:24 ` [PATCH 2/3] riscv: word-at-a-time: improve find_zero() without Zbb Jisheng Zhang
2026-01-13 12:24 ` [PATCH 3/3] riscv: word-at-a-time: improve find_zero() for Zbb Jisheng Zhang
2026-08-17 15:18 ` [PATCH 0/3] riscv: word-at-a-time: improve find_zero() Jisheng Zhang
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