From nobody Fri Jan 2 15:46:14 2026 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 A1A1BCD68FE for ; Tue, 10 Oct 2023 08:27:21 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1442804AbjJJI1T (ORCPT ); Tue, 10 Oct 2023 04:27:19 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:59196 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1442824AbjJJI1K (ORCPT ); Tue, 10 Oct 2023 04:27:10 -0400 Received: from galois.linutronix.de (Galois.linutronix.de [IPv6:2a0a:51c0:0:12e:550::1]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id C40FB107; Tue, 10 Oct 2023 01:27:07 -0700 (PDT) Date: Tue, 10 Oct 2023 08:27:04 -0000 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=linutronix.de; s=2020; t=1696926425; h=from:from:sender:sender:reply-to:reply-to:subject:subject:date:date: message-id:message-id:to:to:cc:cc:mime-version:mime-version: content-type:content-type: content-transfer-encoding:content-transfer-encoding: in-reply-to:in-reply-to:references:references; bh=pNbc6lLzsql6snug0HQa1mxk/kzC8m7f+xiIcj20Lyo=; b=jjk/Std83BJkeIWWgFLY87BoVtjAp+nGXoKw+esUF7jh9w0xLYWuD71Aovoqwz+3zCKBFd ae6xwOCeTLh5m9ROVQEPH97PMAqxfGbOEAcwV60UjqB35cDnBlq3hR9AAi94tn2kj7XHON vHbzJlTWRoBtVsqTUxZGFgdGSp1R77dzhRg9oOn71ArhVfXNEIv4MOA1k3dLYP8DAHDHK1 e4MAuHCrKOr9TyxmFjDx1jiMtSxM0RHwvr5fLHZCT0ADIsf53U0RJMQWAdH5aF/VI8+ngA GoU1QT9Vm+3E6qd/mlzPwqEc2r+spydF3M0lmXalLK1Ca8TWBMF/Ovc2PmOUtA== DKIM-Signature: v=1; a=ed25519-sha256; c=relaxed/relaxed; d=linutronix.de; s=2020e; t=1696926425; h=from:from:sender:sender:reply-to:reply-to:subject:subject:date:date: message-id:message-id:to:to:cc:cc:mime-version:mime-version: content-type:content-type: content-transfer-encoding:content-transfer-encoding: in-reply-to:in-reply-to:references:references; bh=pNbc6lLzsql6snug0HQa1mxk/kzC8m7f+xiIcj20Lyo=; b=o8q/0BKhL6U+WadtrCgQLm20NqhAKcrWI58CKcS0uoxHu08QrdEMyOYDygQR0IHgkP2n05 VuuBOkVB1gQgvbCg== From: "tip-bot2 for Uros Bizjak" Sender: tip-bot2@linutronix.de Reply-to: linux-kernel@vger.kernel.org To: linux-tip-commits@vger.kernel.org Subject: [tip: locking/core] locking/atomics: Use atomic_try_cmpxchg_release() to micro-optimize rcuref_put_slowpath() Cc: Uros Bizjak , Ingo Molnar , Peter Zijlstra , "Paul E. McKenney" , x86@kernel.org, linux-kernel@vger.kernel.org In-Reply-To: <20230509150255.3691-1-ubizjak@gmail.com> References: <20230509150255.3691-1-ubizjak@gmail.com> MIME-Version: 1.0 Message-ID: <169692642491.3135.15300727916265365839.tip-bot2@tip-bot2> Robot-ID: Robot-Unsubscribe: Contact to get blacklisted from these emails Content-Type: text/plain; charset="utf-8" Content-Transfer-Encoding: quoted-printable Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org The following commit has been merged into the locking/core branch of tip: Commit-ID: 4fbf8b136ded943f8661cf48270482ad1f5ce7bd Gitweb: https://git.kernel.org/tip/4fbf8b136ded943f8661cf48270482ad1= f5ce7bd Author: Uros Bizjak AuthorDate: Tue, 09 May 2023 17:02:55 +02:00 Committer: Ingo Molnar CommitterDate: Tue, 10 Oct 2023 10:14:27 +02:00 locking/atomics: Use atomic_try_cmpxchg_release() to micro-optimize rcuref_= put_slowpath() Use atomic_try_cmpxchg() instead of atomic_cmpxchg(*ptr, old, new) =3D=3D o= ld in rcuref_put_slowpath(). On x86 the CMPXCHG instruction returns success in= the ZF flag, so this change saves a compare after CMPXCHG. Additionaly, the compiler reorders some code blocks to follow likely/unlikely annotations in the atomic_try_cmpxchg() macro, improving the code from: 9a: f0 0f b1 0b lock cmpxchg %ecx,(%rbx) 9e: 83 f8 ff cmp $0xffffffff,%eax a1: 74 04 je a7 a3: 31 c0 xor %eax,%eax to: 9a: f0 0f b1 0b lock cmpxchg %ecx,(%rbx) 9e: 75 4c jne ec a0: b0 01 mov $0x1,%al No functional change intended. Signed-off-by: Uros Bizjak Signed-off-by: Ingo Molnar Cc: Peter Zijlstra Cc: Paul E. McKenney Link: https://lore.kernel.org/r/20230509150255.3691-1-ubizjak@gmail.com --- lib/rcuref.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-) diff --git a/lib/rcuref.c b/lib/rcuref.c index 5ec00a4..97f300e 100644 --- a/lib/rcuref.c +++ b/lib/rcuref.c @@ -248,7 +248,7 @@ bool rcuref_put_slowpath(rcuref_t *ref) * require a retry. If this fails the caller is not * allowed to deconstruct the object. */ - if (atomic_cmpxchg_release(&ref->refcnt, RCUREF_NOREF, RCUREF_DEAD) !=3D= RCUREF_NOREF) + if (!atomic_try_cmpxchg_release(&ref->refcnt, &cnt, RCUREF_DEAD)) return false; =20 /*