From patchwork Wed Jul 19 07:00:01 2023 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: Guo Ren X-Patchwork-Id: 13318399 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 20140C0015E for ; Wed, 19 Jul 2023 07:00:16 +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: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:In-Reply-To:References: List-Owner; bh=b2duZGZ4Ztf4C/ShlE/DgyCU3wWZYrWuZ9LiunI39pk=; b=JfGg+lBPo+ULaS ROYiscDNSvAvnd0jKSwEo8CIdc852SL9KgE+xEBcHpa1YI6F24n6WWR/04ng+dL6i3j3eDC6h4pR+ 4D3hHTkjwzM5ZWroa7y8XjZbeZXFwBf0Ts+eOQyJrW8/UpG82wQlqHvO00DufxBhqtNgjhepB71Uh iMDPKIH20iLzP0XTpIL5Dj7Bk4jtZqmeUAOCY4EX/8b93Sf2vFgsqs5Dk2jKiJujPI2EebHnNsxqP h3CgztrdRyBd+x/VaZhxCH+Nl76FPoOkaDSXdb0q6aAhl/L2is3xp2m6aDbYbwNHh/W0Is5hUuMny +CQiDkMAAslYdCYsDs7A==; Received: from localhost ([::1] helo=bombadil.infradead.org) by bombadil.infradead.org with esmtp (Exim 4.96 #2 (Red Hat Linux)) id 1qM1AS-0061Ai-2w; Wed, 19 Jul 2023 07:00:12 +0000 Received: from dfw.source.kernel.org ([2604:1380:4641:c500::1]) by bombadil.infradead.org with esmtps (Exim 4.96 #2 (Red Hat Linux)) id 1qM1AQ-00619U-1V for linux-riscv@lists.infradead.org; Wed, 19 Jul 2023 07:00:11 +0000 Received: from smtp.kernel.org (relay.kernel.org [52.25.139.140]) (using TLSv1.3 with cipher TLS_AES_256_GCM_SHA384 (256/256 bits) key-exchange X25519 server-signature RSA-PSS (2048 bits)) (No client certificate requested) by dfw.source.kernel.org (Postfix) with ESMTPS id 7119F611DC; Wed, 19 Jul 2023 07:00:09 +0000 (UTC) Received: by smtp.kernel.org (Postfix) with ESMTPSA id 93359C433C7; Wed, 19 Jul 2023 07:00:06 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1689750008; bh=HDeq1/IS5rQ4pnF29vgg6/9UWwbJAWwzrpsSqnIsDaw=; h=From:To:Cc:Subject:Date:From; b=BlcMRpZXnKySXsRU/BLq7GNtkEcIqOSpQtkb9tE+IHnV5dfCtpRdy8Vot8NgHZKEP 5icYatEmT1Aeu0O4/z2ZhmvRY5EgFlT6p3jxOlyN+gCF8vtHejFG7QaBqMOZaRjBr5 hqrDu9imKG4cshkQ0M33xGa+SEspuW5tYh4BSy562wAcV2CAlsgDziRsbcWcnHz1t1 An8hZxwQ24hbu7bfU+NbBXcNxbf9sxSvTcQWrlM7H0NI+6fcaRXGG4nwEEo3EL2d6N ZSFNO42cUZMlt9PtQjmqMU4BDQ2dcYRxqdryZnYIsKeKzbVFt7GawtHarwukr6Dy3m paPXR9B6ffsBQ== From: guoren@kernel.org To: guoren@kernel.org, David.Laight@ACULAB.COM, will@kernel.org, peterz@infradead.org, mingo@redhat.com, longman@redhat.com Cc: linux-arch@vger.kernel.org, linux-kernel@vger.kernel.org, linux-riscv@lists.infradead.org, Guo Ren Subject: [PATCH] asm-generic: ticket-lock: Optimize arch_spin_value_unlocked Date: Wed, 19 Jul 2023 03:00:01 -0400 Message-Id: <20230719070001.795010-1-guoren@kernel.org> X-Mailer: git-send-email 2.36.1 MIME-Version: 1.0 X-CRM114-Version: 20100106-BlameMichelson ( TRE 0.8.0 (BSD) ) MR-646709E3 X-CRM114-CacheID: sfid-20230719_000010_565197_9564D5BC X-CRM114-Status: GOOD ( 10.45 ) 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 From: Guo Ren Using arch_spinlock_is_locked would cause another unnecessary memory access to the contended value. Although it won't cause a significant performance gap in most architectures, the arch_spin_value_unlocked argument contains enough information. Thus, remove unnecessary atomic_read in arch_spin_value_unlocked(). Signed-off-by: Guo Ren Signed-off-by: Guo Ren Cc: David Laight Cc: Peter Zijlstra --- Changelog: This patch is separate from: https://lore.kernel.org/linux-riscv/20220808071318.3335746-1-guoren@kernel.org/ Peter & David have commented on it: https://lore.kernel.org/linux-riscv/YsK4Z9w0tFtgkni8@hirez.programming.kicks-ass.net/ --- include/asm-generic/spinlock.h | 16 +++++++++------- 1 file changed, 9 insertions(+), 7 deletions(-) diff --git a/include/asm-generic/spinlock.h b/include/asm-generic/spinlock.h index fdfebcb050f4..90803a826ba0 100644 --- a/include/asm-generic/spinlock.h +++ b/include/asm-generic/spinlock.h @@ -68,11 +68,18 @@ static __always_inline void arch_spin_unlock(arch_spinlock_t *lock) smp_store_release(ptr, (u16)val + 1); } +static __always_inline int arch_spin_value_unlocked(arch_spinlock_t lock) +{ + u32 val = lock.counter; + + return ((val >> 16) == (val & 0xffff)); +} + static __always_inline int arch_spin_is_locked(arch_spinlock_t *lock) { - u32 val = atomic_read(lock); + arch_spinlock_t val = READ_ONCE(*lock); - return ((val >> 16) != (val & 0xffff)); + return !arch_spin_value_unlocked(val); } static __always_inline int arch_spin_is_contended(arch_spinlock_t *lock) @@ -82,11 +89,6 @@ static __always_inline int arch_spin_is_contended(arch_spinlock_t *lock) return (s16)((val >> 16) - (val & 0xffff)) > 1; } -static __always_inline int arch_spin_value_unlocked(arch_spinlock_t lock) -{ - return !arch_spin_is_locked(&lock); -} - #include #endif /* __ASM_GENERIC_SPINLOCK_H */