From mboxrd@z Thu Jan  1 00:00:00 1970
Received: from out30-110.freemail.mail.aliyun.com (out30-110.freemail.mail.aliyun.com [115.124.30.110])
	(using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits))
	(No client certificate requested)
	by smtp.subspace.kernel.org (Postfix) with ESMTPS id 636B039D6E9
	for <linux-kernel@vger.kernel.org>; Fri, 10 Apr 2026 11:36:53 +0000 (UTC)
Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=115.124.30.110
ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116;
	t=1775821016; cv=none; b=qw1tX4543184TKB44XeOKjeoqbLwuqlS9zpdfjUOe1bjwOwQ+Gq/rOY40500Z5Jc5es/1uY3Q3We+j9ZfS1E6UCx2P0RvvR0AgZADodmmG641MOR23j8Pi6/cTS68I+nsyALi6uVsO2n6dUFY6HuwRHXEORGmSyM8gofG9YxUgk=
ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org;
	s=arc-20240116; t=1775821016; c=relaxed/simple;
	bh=3Cnlm5srbNoVb/O2/CtPP+M2xvIGy7mu/NKH5jrS7Ww=;
	h=From:To:Cc:Subject:Date:Message-ID:In-Reply-To:References:
	 MIME-Version; b=uNKXmJQOwTF2aylRn+PlCVKP+U98DR129IiSuBL6KluxLzGBpk5TE5CZLiQ6ruMpyDf1hivZTf2CNZRbpD9kyF6H83yLLRZT1vKR/E1cD+J96bzPXvLSMq7RwDfUCp1heOB/nnDaGEqO7Lz3xjlTH/2FB4hjH5RFpiMnZ+viJOg=
ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=linux.alibaba.com; spf=pass smtp.mailfrom=linux.alibaba.com; dkim=pass (1024-bit key) header.d=linux.alibaba.com header.i=@linux.alibaba.com header.b=C3cwMTWS; arc=none smtp.client-ip=115.124.30.110
Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=linux.alibaba.com
Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=linux.alibaba.com
Authentication-Results: smtp.subspace.kernel.org;
	dkim=pass (1024-bit key) header.d=linux.alibaba.com header.i=@linux.alibaba.com header.b="C3cwMTWS"
DKIM-Signature:v=1; a=rsa-sha256; c=relaxed/relaxed;
	d=linux.alibaba.com; s=default;
	t=1775821010; h=From:To:Subject:Date:Message-ID:MIME-Version;
	bh=i14BS7GrqYV7Zzk+pfr2uQL5MKpn/DMYLWddS0YiJzY=;
	b=C3cwMTWSzw8h0qVOc9UyijEv+xqr/K4NoDd2qLqzXRzlWSGEH9f1uu+/YxgQ6tYp5YouKGr/93rcYKEjs+e6DlaoI9KuMjnovHhRuy/qWZmlXAORKMItvhQA6j7UFSrqEQtKPnvKBJ/s0BdKrAjliBDFgS6c5tV3THIgXkKuec8=
X-Alimail-AntiSpam:AC=PASS;BC=-1|-1;BR=01201311R191e4;CH=green;DM=||false|;DS=||;FP=0|-1|-1|-1|0|-1|-1|-1;HT=maildocker-contentspam033037026112;MF=cp0613@linux.alibaba.com;NM=1;PH=DS;RN=8;SR=0;TI=SMTPD_---0X0l8ghE_1775821001;
Received: from DESKTOP-S9E58SO.localdomain(mailfrom:cp0613@linux.alibaba.com fp:SMTPD_---0X0l8ghE_1775821001 cluster:ay36)
          by smtp.aliyun-inc.com;
          Fri, 10 Apr 2026 19:36:50 +0800
From: cp0613@linux.alibaba.com
To: ruanjinjie@huawei.com
Cc: akpm@linux-foundation.org,
	alex@ghiti.fr,
	aou@eecs.berkeley.edu,
	linux-kernel@vger.kernel.org,
	linux-riscv@lists.infradead.org,
	palmer@dabbelt.com,
	pjw@kernel.org
Subject: Re: [PATCH] arch/riscv: Add bitrev.h file to support rev8 and brev8
Date: Fri, 10 Apr 2026 19:36:40 +0800
Message-ID: <20260410113640.106730-1-cp0613@linux.alibaba.com>
X-Mailer: git-send-email 2.43.0
In-Reply-To: <20260311071344.3305640-1-ruanjinjie@huawei.com>
References: <20260311071344.3305640-1-ruanjinjie@huawei.com>
Precedence: bulk
X-Mailing-List: linux-kernel@vger.kernel.org
List-Id: <linux-kernel.vger.kernel.org>
List-Subscribe: <mailto:linux-kernel+subscribe@vger.kernel.org>
List-Unsubscribe: <mailto:linux-kernel+unsubscribe@vger.kernel.org>
MIME-Version: 1.0
Content-Transfer-Encoding: 8bit

On Wed, 11 Mar 2026 15:13:44 +0800, ruanjinjie@huawei.com wrote:

> +#include <linux/types.h>
> +#include <asm/cpufeature-macros.h>
> +#include <asm/hwcap.h>
> +
> +extern u8 const byte_rev_table[256];
> +static __always_inline __attribute_const__ u32 __arch_bitrev32(u32 x)
> +{
> +	if (IS_ENABLED(CONFIG_RISCV_ISA_ZBKB) &&
> +	    riscv_has_extension_likely(RISCV_ISA_EXT_ZBKB)) {
> +		unsigned long result = x;
> +
> +		asm volatile(
> +			".option push\n"
> +			".option arch,+zbkb\n"
> +			"rev8 %0, %0\n"
> +			"brev8 %0, %0\n"
> +			".option pop"
> +			: "+r" (result)
> +		);
> +
> +		if (__riscv_xlen == 64)
> +			return (u32)(result >> 32);
> +
> +		return (u32)result;
> +	}
> +
> +	return (u32)byte_rev_table[x & 0xff] << 24 |
> +	       (u32)byte_rev_table[(x >> 8) & 0xff] << 16 |
> +	       (u32)byte_rev_table[(x >> 16) & 0xff] << 8 |
> +	       (u32)byte_rev_table[x >> 24];
> +}

Hi Jinjie,

Thanks for your patch. I have two suggestions.
1. When ZBKB is not supported, is it simpler to directly use the generic
implementation __bitrev32 in <linux/bitrev.h>.
2. Could you please provide a benchmark test case to illustrate the
performance comparison with and without this extension (refer to
test_bitops.c) and also provide the results by bloat-o-meter.

Thanks,
Pei