From: Nam Cao <namcao@linutronix.de>
To: Jisheng Zhang <jszhang@kernel.org>,
Paul Walmsley <pjw@kernel.org>,
Palmer Dabbelt <palmer@dabbelt.com>,
Albert Ou <aou@eecs.berkeley.edu>,
Alexandre Ghiti <alex@ghiti.fr>
Cc: 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, 20 Aug 2026 10:31:49 +0200 [thread overview]
Message-ID: <87mruh5h1m.fsf@yellow.woof> (raw)
In-Reply-To: <20260113122457.27507-2-jszhang@kernel.org>
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?
Nam
WARNING: multiple messages have this Message-ID (diff)
From: Nam Cao <namcao@linutronix.de>
To: Jisheng Zhang <jszhang@kernel.org>,
Paul Walmsley <pjw@kernel.org>,
Palmer Dabbelt <palmer@dabbelt.com>,
Albert Ou <aou@eecs.berkeley.edu>,
Alexandre Ghiti <alex@ghiti.fr>
Cc: 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, 20 Aug 2026 10:31:49 +0200 [thread overview]
Message-ID: <87mruh5h1m.fsf@yellow.woof> (raw)
In-Reply-To: <20260113122457.27507-2-jszhang@kernel.org>
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?
Nam
_______________________________________________
linux-riscv mailing list
linux-riscv@lists.infradead.org
http://lists.infradead.org/mailman/listinfo/linux-riscv
next prev parent reply other threads:[~2026-08-20 8:31 UTC|newest]
Thread overview: 12+ 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 ` Jisheng Zhang
2026-01-13 12:24 ` [PATCH 1/3] riscv: word-at-a-time: improve find_zero() for !RISCV_ISA_ZBB Jisheng Zhang
2026-01-13 12:24 ` Jisheng Zhang
2026-08-20 8:31 ` Nam Cao [this message]
2026-08-20 8:31 ` Nam Cao
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 ` Jisheng Zhang
2026-01-13 12:24 ` [PATCH 3/3] riscv: word-at-a-time: improve find_zero() for Zbb Jisheng Zhang
2026-01-13 12:24 ` Jisheng Zhang
2026-08-17 15:18 ` [PATCH 0/3] riscv: word-at-a-time: improve find_zero() Jisheng Zhang
2026-08-17 15:18 ` Jisheng Zhang
Reply instructions:
You may reply publicly to this message via plain-text email
using any one of the following methods:
* Save the following mbox file, import it into your mail client,
and reply-to-all from there: mbox
Avoid top-posting and favor interleaved quoting:
https://en.wikipedia.org/wiki/Posting_style#Interleaved_style
* Reply using the --to, --cc, and --in-reply-to
switches of git-send-email(1):
git send-email \
--in-reply-to=87mruh5h1m.fsf@yellow.woof \
--to=namcao@linutronix.de \
--cc=alex@ghiti.fr \
--cc=aou@eecs.berkeley.edu \
--cc=jszhang@kernel.org \
--cc=linux-kernel@vger.kernel.org \
--cc=linux-riscv@lists.infradead.org \
--cc=palmer@dabbelt.com \
--cc=pjw@kernel.org \
/path/to/YOUR_REPLY
https://kernel.org/pub/software/scm/git/docs/git-send-email.html
* If your mail client supports setting the In-Reply-To header
via mailto: links, try the mailto: link
Be sure your reply has a Subject: header at the top and a blank line
before the message body.
This is an external index of several public inboxes,
see mirroring instructions on how to clone and mirror
all data and code used by this external index.