From patchwork Sun Jan 15 15:49:46 2023 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: Jisheng Zhang X-Patchwork-Id: 13102317 X-Patchwork-Delegate: palmer@dabbelt.com 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 bombadil.infradead.org (bombadil.infradead.org [198.137.202.133]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.lore.kernel.org (Postfix) with ESMTPS id 58601C3DA78 for ; Sun, 15 Jan 2023 16:00:49 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; d=lists.infradead.org; s=bombadil.20210309; h=Sender: Content-Transfer-Encoding:Content-Type:List-Subscribe:List-Help:List-Post: List-Archive:List-Unsubscribe:List-Id:MIME-Version:References:In-Reply-To: Message-Id:Date:Subject:Cc:To:From:Reply-To:Content-ID:Content-Description: Resent-Date:Resent-From:Resent-Sender:Resent-To:Resent-Cc:Resent-Message-ID: List-Owner; bh=wLvGjHQcF5DfCiz2Plm4LRxjoawr3jeHf6xAJ5RMC3A=; b=g2dlsDjFA0XnwO oHLH9KC4t8jyCkM7wXHTchr8U2SnGi4ypBMUFtIUG0hB7icGPY6XtOjjuMff/ED7UC61Yak0FHh/y w9ppJkwArJ8+fNdx+mKxUbUjv8XKsw08/6yS1/eJpgBdJrBkGyClhax53k9FS22ylBq6f9ZwuIbiv 487mkBJc0kDrcusBmmIUk/sJEYPauCh6KxlDWc9nf32eVMKFA3+HygukKVT7+CKtX6VfL9A69+7kv 4e8Q99yb531N/FS5weSaENGP+RCoq9qBTtpLU+flFQWm648HlOyWLJTZrFdBmYuQnOvbTnDUKLByM tKIlCPWMFvdK6PKnCo6Q==; Received: from localhost ([::1] helo=bombadil.infradead.org) by bombadil.infradead.org with esmtp (Exim 4.94.2 #2 (Red Hat Linux)) id 1pH5R4-007bxC-DF; Sun, 15 Jan 2023 16:00:42 +0000 Received: from dfw.source.kernel.org ([2604:1380:4641:c500::1]) by bombadil.infradead.org with esmtps (Exim 4.94.2 #2 (Red Hat Linux)) id 1pH5Qt-007bmw-Ef; Sun, 15 Jan 2023 16:00:35 +0000 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 dfw.source.kernel.org (Postfix) with ESMTPS id F134F60DB6; Sun, 15 Jan 2023 16:00:30 +0000 (UTC) Received: by smtp.kernel.org (Postfix) with ESMTPSA id 3F974C433F0; Sun, 15 Jan 2023 16:00:28 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1673798430; bh=mINO93PYoIl2Le02IWiuk8J2800U31qq9j/6NT8h4Nc=; h=From:To:Cc:Subject:Date:In-Reply-To:References:From; b=DdrgAsgwrTvTsV6VHjq5HTcb1PpoZm4hZ2OiXa0qNIfHZpNilj3/svAWkCIIQwZfF sMNXFzpEUcY7KaCZaBVOrsK/SjzGUbHbUWEokDTP1Z+QHPgetuKInyabh5gfOx7N4L LOV6TCGxm8k8bmSfjuW7oFyx6AJtx2Hay9OgA2dBbtmSegYN1LQ+Dd4ZcC/G3aiqkd Tfr/qdVaNM4cC5nzilR3UMo6sGeFDtN5OjFab9I8gOsKsT2WSjZDgyi/gml9aKC0Yr B0k1S961lgZL+X1DvBxw5/yGW22vZC1IWYrsuggZ80WnDAHrg6/653v3f6U2gmLKSq GMdVdPE2bainA== From: Jisheng Zhang To: Paul Walmsley , Palmer Dabbelt , Albert Ou , Anup Patel , Atish Patra , Heiko Stuebner , Conor Dooley , Andrew Jones Cc: linux-riscv@lists.infradead.org, linux-kernel@vger.kernel.org, kvm@vger.kernel.org, kvm-riscv@lists.infradead.org Subject: [PATCH v4 06/13] riscv: introduce riscv_has_extension_[un]likely() Date: Sun, 15 Jan 2023 23:49:46 +0800 Message-Id: <20230115154953.831-7-jszhang@kernel.org> X-Mailer: git-send-email 2.38.1 In-Reply-To: <20230115154953.831-1-jszhang@kernel.org> References: <20230115154953.831-1-jszhang@kernel.org> MIME-Version: 1.0 X-CRM114-Version: 20100106-BlameMichelson ( TRE 0.8.0 (BSD) ) MR-646709E3 X-CRM114-CacheID: sfid-20230115_080033_343018_F650D255 X-CRM114-Status: GOOD ( 13.88 ) X-BeenThere: linux-riscv@lists.infradead.org X-Mailman-Version: 2.1.34 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Sender: "linux-riscv" Errors-To: linux-riscv-bounces+linux-riscv=archiver.kernel.org@lists.infradead.org Generally, riscv ISA extensions are fixed for any specific hardware platform, so a hart's features won't change after booting. This chacteristic makes it straightforward to use a static branch to check if a specific ISA extension is supported or not to optimize performance. However, some ISA extensions such as SVPBMT and ZICBOM are handled via. the alternative sequences. 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." 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. 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. Link: https://lore.kernel.org/linux-riscv/20220922060958.44203-1-samuel@sholland.org/ [1] Link: https://lore.kernel.org/linux-arm-kernel/20220912162210.3626215-8-mark.rutland@arm.com/ [2] Signed-off-by: Jisheng Zhang Reviewed-by: Andrew Jones Acked-by: Conor Dooley --- arch/riscv/include/asm/hwcap.h | 37 ++++++++++++++++++++++++++++++++++ 1 file changed, 37 insertions(+) diff --git a/arch/riscv/include/asm/hwcap.h b/arch/riscv/include/asm/hwcap.h index 09a7767723f6..1767a9ce1a04 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 +#include #include #include #include @@ -97,6 +98,42 @@ static __always_inline int riscv_isa_ext2key(int num) } } +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); #define riscv_isa_extension_mask(ext) BIT_MASK(RISCV_ISA_EXT_##ext)