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[2620:137:e000::1:20]) by mx.google.com with ESMTP id v22-20020a056402185600b0051bfd21d20fsi2510045edy.87.2023.07.19.00.21.34; Wed, 19 Jul 2023 00:21:58 -0700 (PDT) Received-SPF: pass (google.com: domain of linux-kernel-owner@vger.kernel.org designates 2620:137:e000::1:20 as permitted sender) client-ip=2620:137:e000::1:20; Authentication-Results: mx.google.com; dkim=pass header.i=@kernel.org header.s=k20201202 header.b=BlcMRpZX; spf=pass (google.com: domain of linux-kernel-owner@vger.kernel.org designates 2620:137:e000::1:20 as permitted sender) smtp.mailfrom=linux-kernel-owner@vger.kernel.org; dmarc=pass (p=NONE sp=NONE dis=NONE) header.from=kernel.org Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S230116AbjGSHAN (ORCPT + 99 others); Wed, 19 Jul 2023 03:00:13 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:42200 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S229918AbjGSHAK (ORCPT ); Wed, 19 Jul 2023 03:00:10 -0400 Received: from dfw.source.kernel.org (dfw.source.kernel.org [139.178.84.217]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id E341F10A; Wed, 19 Jul 2023 00:00:09 -0700 (PDT) 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 78A0F61275; 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-Spam-Status: No, score=-7.1 required=5.0 tests=BAYES_00,DKIMWL_WL_HIGH, DKIM_SIGNED,DKIM_VALID,DKIM_VALID_AU,DKIM_VALID_EF,RCVD_IN_DNSWL_HI, SPF_HELO_NONE,SPF_PASS,T_SCC_BODY_TEXT_LINE autolearn=ham autolearn_force=no version=3.4.6 X-Spam-Checker-Version: SpamAssassin 3.4.6 (2021-04-09) on lindbergh.monkeyblade.net Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org X-getmail-retrieved-from-mailbox: INBOX X-GMAIL-THRID: 1771832678144753733 X-GMAIL-MSGID: 1771832678144753733 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 */