From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by smtp.lore.kernel.org (Postfix) with ESMTP id E8649C352A1 for ; Tue, 6 Dec 2022 20:25:44 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S229564AbiLFUZo (ORCPT ); Tue, 6 Dec 2022 15:25:44 -0500 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:57996 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S229475AbiLFUZm (ORCPT ); Tue, 6 Dec 2022 15:25:42 -0500 Received: from ams.source.kernel.org (ams.source.kernel.org [145.40.68.75]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 8CB51DF88; Tue, 6 Dec 2022 12:25:41 -0800 (PST) Received: from smtp.kernel.org (relay.kernel.org [52.25.139.140]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by ams.source.kernel.org (Postfix) with ESMTPS id 46E66B81B33; Tue, 6 Dec 2022 20:25:40 +0000 (UTC) Received: by smtp.kernel.org (Postfix) with ESMTPSA id 8399EC433D6; Tue, 6 Dec 2022 20:25:36 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1670358338; bh=NiR96ZKIvW7IpMispdHsgp2vT3FznbdvWds2IP2JVJs=; h=Date:From:To:Cc:Subject:References:In-Reply-To:From; b=SQJ0xRSfGyt/EXVAtU8bHfgHspMYXuVOvWLqR/ovxSWRsgZHSw5L8LCDroazamMym IHqNu1g6g/kyotibAwUMred1WrpsoMAPImQGefc4DYXrOdrgw8fAawTSWGq0h4Wi9r CMd3P8V+cdPsG7LVmtibwhza1R6ReLm7VZi5lNEg1NvKCnDv6U8CL8CDYxXC+s4uDl I+AzxmxLGbGjRqSd9NdLpll15a8EqeSxZY34uM+aUlm8HP9tNFF67zu4a9huKBMsx0 pqtLaO/fthDy4dCwev8aF6IvXXrUoub6FDpGwpuFOmpSeEWGVyQ1NY7YIsWaeNMF+i eTcj/cpdlspZA== Date: Tue, 6 Dec 2022 20:25:34 +0000 From: Conor Dooley To: Jisheng Zhang Cc: Palmer Dabbelt , Paul Walmsley , Albert Ou , Anup Patel , Atish Patra , Heiko Stuebner , Andrew Jones , linux-riscv@lists.infradead.org, linux-kernel@vger.kernel.org, kvm@vger.kernel.org, kvm-riscv@lists.infradead.org Subject: Re: [PATCH v2 06/13] riscv: introduce riscv_has_extension_[un]likely() Message-ID: References: <20221204174632.3677-1-jszhang@kernel.org> <20221204174632.3677-7-jszhang@kernel.org> MIME-Version: 1.0 Content-Type: multipart/signed; micalg=pgp-sha256; protocol="application/pgp-signature"; boundary="bxEn+e9TeJ7KX+1L" Content-Disposition: inline In-Reply-To: <20221204174632.3677-7-jszhang@kernel.org> Precedence: bulk List-ID: X-Mailing-List: kvm@vger.kernel.org --bxEn+e9TeJ7KX+1L Content-Type: text/plain; charset=us-ascii Content-Disposition: inline Content-Transfer-Encoding: quoted-printable Hey Jisheng, Just a couple really minor bits here... On Mon, Dec 05, 2022 at 01:46:25AM +0800, Jisheng Zhang wrote: > Generally, riscv ISA extensions are fixed for any specific hardware > platform, that's to say, the hart features won't change any more s/that's to say, the hart/so a hart's/ s/any more// > after booting, this chacteristic make it straightforward to use "booting. This characteristic makes it" > static branch to check one specific ISA extension is supported or not "a static branch to check if a" > to optimize performance. >=20 > However, some ISA extensions such as SVPBMT and ZICBOM are handled > via. the alternative sequences. >=20 > Basically, for ease of maintenance, we prefer to use static branches > in C code, but recently, Samuel found that the static branch usage in > cpu_relax() breaks building with CONFIG_CC_OPTIMIZE_FOR_SIZE[1]. As > Samuel pointed out, "Having a static branch in cpu_relax() is > problematic because that function is widely inlined, including in some > quite complex functions like in the VDSO. A quick measurement shows > this static branch is responsible by itself for around 40% of the jump > table." >=20 > Samuel's findings pointed out one of a few downsides of static branches > usage in C code to handle ISA extensions detected at boot time: > static branch's metadata in the __jump_table section, which is not > discarded after ISA extensions are finalized, wastes some space. >=20 > I want to try to solve the issue for all possible dynamic handling of > ISA extensions at boot time. Inspired by Mark[2], this patch introduces > riscv_has_extension_*() helpers, which work like static branches but > are patched using alternatives, thus the metadata can be freed after > patching. >=20 > [1]https://lore.kernel.org/linux-riscv/20220922060958.44203-1-samuel@shol= land.org/ > [2]https://lore.kernel.org/linux-arm-kernel/20220912162210.3626215-8-mark= =2Erutland@arm.com/ Can you make these into Link: tags please (and drop the line between the and the SoB)? So: Link: https://lore.kernel.org/linux-riscv/20220922060958.44203-1-samuel@sho= lland.org/ [1] Link: https://lore.kernel.org/linux-arm-kernel/20220912162210.3626215-8-mar= k.rutland@arm.com/ [2] > Signed-off-by: Jisheng Zhang > Reviewed-by: Andrew Jones Changes themselves look grand, no comments there :) Thanks! Conor. > --- > arch/riscv/include/asm/hwcap.h | 37 ++++++++++++++++++++++++++++++++++ > 1 file changed, 37 insertions(+) >=20 > diff --git a/arch/riscv/include/asm/hwcap.h b/arch/riscv/include/asm/hwca= p.h > index 996884986fea..e2d3f6df7701 100644 > --- a/arch/riscv/include/asm/hwcap.h > +++ b/arch/riscv/include/asm/hwcap.h > @@ -8,6 +8,7 @@ > #ifndef _ASM_RISCV_HWCAP_H > #define _ASM_RISCV_HWCAP_H > =20 > +#include > #include > #include > #include > @@ -96,6 +97,42 @@ static __always_inline int riscv_isa_ext2key(int num) > } > } > =20 > +static __always_inline bool > +riscv_has_extension_likely(const unsigned long ext) > +{ > + compiletime_assert(ext < RISCV_ISA_EXT_MAX, > + "ext must be < RISCV_ISA_EXT_MAX"); > + > + asm_volatile_goto( > + ALTERNATIVE("j %l[l_no]", "nop", 0, %[ext], 1) > + : > + : [ext] "i" (ext) > + : > + : l_no); > + > + return true; > +l_no: > + return false; > +} > + > +static __always_inline bool > +riscv_has_extension_unlikely(const unsigned long ext) > +{ > + compiletime_assert(ext < RISCV_ISA_EXT_MAX, > + "ext must be < RISCV_ISA_EXT_MAX"); > + > + asm_volatile_goto( > + ALTERNATIVE("nop", "j %l[l_yes]", 0, %[ext], 1) > + : > + : [ext] "i" (ext) > + : > + : l_yes); > + > + return false; > +l_yes: > + return true; > +} > + > unsigned long riscv_isa_extension_base(const unsigned long *isa_bitmap); > =20 > #define riscv_isa_extension_mask(ext) BIT_MASK(RISCV_ISA_EXT_##ext) > --=20 > 2.37.2 >=20 --bxEn+e9TeJ7KX+1L Content-Type: application/pgp-signature; name="signature.asc" -----BEGIN PGP SIGNATURE----- iHUEABYIAB0WIQRh246EGq/8RLhDjO14tDGHoIJi0gUCY4+lPQAKCRB4tDGHoIJi 0ioQAP4w8r5FQ0ejEXDGcp8UvPntHNhPculcXC9z8LBnhOgVggEAzzZHQlX1lhJN t6WlREfcRjs9PY31RoG5eskhVoUzrg4= =bz9l -----END PGP SIGNATURE----- --bxEn+e9TeJ7KX+1L--