From nobody Sun Feb 8 17:13:17 2026 Received: from galois.linutronix.de (Galois.linutronix.de [193.142.43.55]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id 75F5514F103; Thu, 11 Apr 2024 13:33:46 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=193.142.43.55 ARC-Seal: i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1712842427; cv=none; b=mJXjf9+I9FoyUhbAjnM647Wggqo+HI0kzIahoERdztujEQr0YfEY7WL8c/T/v6wGI1ZTB0MIky1EG004eVyqVjAyx3sAwlew/6dlaSHUH3Y5UMbMXFPxPHNmTPbTdjRGJ6/4rSeUa5EaWt4SIEJ/ymgNF2xB9nh0VKnWrU/PtPY= ARC-Message-Signature: i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1712842427; c=relaxed/simple; bh=92o/s1vjdKCCEAN7tCKADYk7AtNcGSvjS9LNsUv9+2Y=; h=Date:From:To:Subject:Cc:In-Reply-To:References:MIME-Version: Message-ID:Content-Type; b=DvOj47Q2oBpD3BfrM6s5SOsLvaLEhIPGGg8fQO4h2LsVApBrE2na+VCkLwbSQ0ZkKbJMXLU7/eCUwDUJMMlotPxYPKeMfJVwSgjX/sJbP7IW7Esso9FF5mWerdmOE1iaEmUVXKzgn1ISkxDvV6bmvm162SS57NcbM9I0G+q2p3I= ARC-Authentication-Results: i=1; smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=linutronix.de; spf=pass smtp.mailfrom=linutronix.de; dkim=pass (2048-bit key) header.d=linutronix.de header.i=@linutronix.de header.b=CmdTXFzX; dkim=permerror (0-bit key) header.d=linutronix.de header.i=@linutronix.de header.b=JaRrBdqU; arc=none smtp.client-ip=193.142.43.55 Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=linutronix.de Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=linutronix.de Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=linutronix.de header.i=@linutronix.de header.b="CmdTXFzX"; dkim=permerror (0-bit key) header.d=linutronix.de header.i=@linutronix.de header.b="JaRrBdqU" Date: Thu, 11 Apr 2024 13:33:41 -0000 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=linutronix.de; s=2020; t=1712842421; 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=p5wIEDLHP2BJVwrHrqk3PT7SL1PU/3MmNsD2H3lnyhM=; b=CmdTXFzXqa2VMuHxH10kwAOem/Rw2mk26b3buZa7RR/va8nIwUp3Y48UDmRghZXGz+0Tm5 AQ3p6v2aXlu9erzUJKKoVQRILD8RAt91Z9KUefNr9dX3Hm2GHburZ0Nn/fjv4zTgbZvtOa vC0+UvY+ldTjxVAXPCJ0FAf9VLOh4Ck35wgpNg68ZujV/R8Nqpi1RQVtcVeIDt9NqeB2yn fm3SE8eas59IYkDfEeGXXwx7FcKUwUEw2xq6HyTZbZPlVQaHjw2vGQ7EaJLQ8/EadIjJNt VDUPAJidiWvyUp999OIzDJIGWMYuZGN9HQ7FuY60N+TjjVNQcFkYDFrXyitO5w== DKIM-Signature: v=1; a=ed25519-sha256; c=relaxed/relaxed; d=linutronix.de; s=2020e; t=1712842421; 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=p5wIEDLHP2BJVwrHrqk3PT7SL1PU/3MmNsD2H3lnyhM=; b=JaRrBdqUhlqCsOR36ZwJXdBCmEXstnVHCTYdNSOEOojdUG5Fy2eiaucO5lVLFql0PmD0qY KuTpYd/zjttsmDAg== 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/qspinlock: Use atomic_try_cmpxchg_relaxed() in xchg_tail() Cc: Uros Bizjak , Ingo Molnar , Waiman Long , Linus Torvalds , x86@kernel.org, linux-kernel@vger.kernel.org In-Reply-To: <20240321195309.484275-1-ubizjak@gmail.com> References: <20240321195309.484275-1-ubizjak@gmail.com> Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Message-ID: <171284242106.10875.12200696780479010207.tip-bot2@tip-bot2> Robot-ID: Robot-Unsubscribe: Contact to get blacklisted from these emails Precedence: bulk Content-Type: text/plain; charset="utf-8" Content-Transfer-Encoding: quoted-printable The following commit has been merged into the locking/core branch of tip: Commit-ID: 79a34e3d8411050c3c7550c5163d6f9dc41e8f66 Gitweb: https://git.kernel.org/tip/79a34e3d8411050c3c7550c5163d6f9dc= 41e8f66 Author: Uros Bizjak AuthorDate: Thu, 21 Mar 2024 20:52:47 +01:00 Committer: Ingo Molnar CommitterDate: Thu, 11 Apr 2024 15:14:54 +02:00 locking/qspinlock: Use atomic_try_cmpxchg_relaxed() in xchg_tail() Use atomic_try_cmpxchg_relaxed(*ptr, &old, new) instead of atomic_cmpxchg_relaxed (*ptr, old, new) =3D=3D old in xchg_tail(). x86 CMPXCHG instruction returns success in ZF flag, so this change saves a compare after CMPXCHG. No functional change intended. Since this code requires NR_CPUS >=3D 16k, I have tested it by unconditionally setting _Q_PENDING_BITS to 1 in . Signed-off-by: Uros Bizjak Signed-off-by: Ingo Molnar Reviewed-by: Waiman Long Cc: Linus Torvalds Link: https://lore.kernel.org/r/20240321195309.484275-1-ubizjak@gmail.com --- kernel/locking/qspinlock.c | 13 +++++-------- 1 file changed, 5 insertions(+), 8 deletions(-) diff --git a/kernel/locking/qspinlock.c b/kernel/locking/qspinlock.c index ebe6b8e..1df5fef 100644 --- a/kernel/locking/qspinlock.c +++ b/kernel/locking/qspinlock.c @@ -220,21 +220,18 @@ static __always_inline void clear_pending_set_locked(= struct qspinlock *lock) */ static __always_inline u32 xchg_tail(struct qspinlock *lock, u32 tail) { - u32 old, new, val =3D atomic_read(&lock->val); + u32 old, new; =20 - for (;;) { - new =3D (val & _Q_LOCKED_PENDING_MASK) | tail; + old =3D atomic_read(&lock->val); + do { + new =3D (old & _Q_LOCKED_PENDING_MASK) | tail; /* * We can use relaxed semantics since the caller ensures that * the MCS node is properly initialized before updating the * tail. */ - old =3D atomic_cmpxchg_relaxed(&lock->val, val, new); - if (old =3D=3D val) - break; + } while (!atomic_try_cmpxchg_relaxed(&lock->val, &old, new)); =20 - val =3D old; - } return old; } #endif /* _Q_PENDING_BITS =3D=3D 8 */