From nobody Sat Feb 7 17:20:34 2026 Received: from mail-wm1-f42.google.com (mail-wm1-f42.google.com [209.85.128.42]) (using TLSv1.2 with cipher ECDHE-RSA-AES128-GCM-SHA256 (128/128 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id 99DE113442E for ; Thu, 21 Mar 2024 19:53:24 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=209.85.128.42 ARC-Seal: i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1711050806; cv=none; b=didTQI+GrfZHjv4n9jpce694ESy7hoYmzDgxY7XGGc4Qu+/hNi5I+HZhs/6ZJfKDEguXaimPV0pyWNg4f3nrxPQ3fzq9NpdpDvaYek1alaBsolrykKTgW3b+qeHTbqlpFwpn7EfXUBG33x2cN60w7dcMMloJQ95RtL/49Fr8rjo= ARC-Message-Signature: i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1711050806; c=relaxed/simple; bh=nD8cOpq49+66zTur5Rx14smVkvFzE0T/lc1mTbbANIo=; h=From:To:Cc:Subject:Date:Message-ID:MIME-Version; b=BYqgtlHucBpjxgYdB5M966X59wKx7CNWo23GxPye+/+Ia4TEEEoR0D9Nce8STumrP51LVhbYB7FHmt+7yXC7Rj2XcwQI8VNSWtccccT4wWqx34++hJrpgwe9AZCHiK/EBcllE7PAbKgQV1sgb4ZZHb+MK39TQG2r/n3ZpYPoAY0= ARC-Authentication-Results: i=1; smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=gmail.com; spf=pass smtp.mailfrom=gmail.com; dkim=pass (2048-bit key) header.d=gmail.com header.i=@gmail.com header.b=DbC2UZpu; arc=none smtp.client-ip=209.85.128.42 Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=gmail.com Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=gmail.com Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=gmail.com header.i=@gmail.com header.b="DbC2UZpu" Received: by mail-wm1-f42.google.com with SMTP id 5b1f17b1804b1-4146f2bf8ecso9818195e9.3 for ; Thu, 21 Mar 2024 12:53:24 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=gmail.com; s=20230601; t=1711050802; x=1711655602; darn=vger.kernel.org; h=content-transfer-encoding:mime-version:message-id:date:subject:cc :to:from:from:to:cc:subject:date:message-id:reply-to; bh=ZWCv4bEtMtvoPMEGevXwNgVJxevtU1V2OzneMTeW1s0=; b=DbC2UZpuMxbYX7kx+3QwVSFzBBiKD655onNOe7GtsuZsdLDVD3lnooxrUFZlwrnKZF 6gKtIXeVJZyIFW++sxG62nV6ulhsmzDwW0GRbH5zJrIgmUnTCUAJXTa7dbOjDz/5SdDj m0f7KmPeI1opxUJHPcXX9HNDmBPlysGuB6iZogCv+jg9a+Hrcbl7vU+BbSq2B2rQsR0Z C1z/INajr1y+noCWG4suwq1DSicCnTzopLQyihb6t4Xu01OBAFqLFv6PAgaJz3Tio1/h w8SEk5qQFOPHyWYiJ7xt93TyvGeWup/D8RMB0S4i5PNv9NmgVchqoEyeD5ImZNGuLY6Q pXsg== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20230601; t=1711050802; x=1711655602; h=content-transfer-encoding:mime-version:message-id:date:subject:cc :to:from:x-gm-message-state:from:to:cc:subject:date:message-id :reply-to; bh=ZWCv4bEtMtvoPMEGevXwNgVJxevtU1V2OzneMTeW1s0=; b=eUTNlswkR5Fi72ebSjWCr8BgtKOjk2C7s35hS2busuuIkNVAma4dy9Uoz63Q0PSrP+ TLkW3p0K8AF20uMU7uZfi66vctn33LKp6dMRkriu6LqAFj3k3fnfpW6MY9yb5d5w3WE1 Llx0k2SJe8u5LcetnDhhfhXX/y9BoQNWRL7L+1Mx5SKCegDMTFmlwP34tM+LXrcGU121 WQZMFbImyjwQtvfAZk5dH2yELeuCAFSHuuRtv5H3GA6/JyCwaRwTcAv1kfcCpRxPwA6z jCObsWfSevH0zwnV1KX7/9dSxElgcqFXjIjNzFqkoXZofA4mhgsePkufhB7fIhIaE6lS i04g== X-Gm-Message-State: AOJu0YxR8Jz/bQadDEyxPwtpp4uJd4xjNljDhxnpLpgABXn2mC7vFoMY oWwc+utWRYMMPvIzqiirDf7hvPlx0RfUGi3V/JsE46mhwm8nyO+93W+oRlRo X-Google-Smtp-Source: AGHT+IEUs5lD9yNsBYQVWu4tJ6B7NxF6YLFedFsTLMUPYCnNirduu3mjEFZEDMun2hXs79+v+oY4VA== X-Received: by 2002:adf:e391:0:b0:33e:737f:9363 with SMTP id e17-20020adfe391000000b0033e737f9363mr85099wrm.70.1711050801793; Thu, 21 Mar 2024 12:53:21 -0700 (PDT) Received: from localhost.localdomain ([46.248.82.114]) by smtp.gmail.com with ESMTPSA id dj9-20020a0560000b0900b0033ec812ee0esm339613wrb.71.2024.03.21.12.53.20 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Thu, 21 Mar 2024 12:53:21 -0700 (PDT) From: Uros Bizjak To: linux-kernel@vger.kernel.org Cc: Uros Bizjak , Peter Zijlstra , Ingo Molnar , Will Deacon , Waiman Long , Boqun Feng Subject: [PATCH] locking/qspinlock: Use atomic_try_cmpxchg_relaxed() in xchg_tail() Date: Thu, 21 Mar 2024 20:52:47 +0100 Message-ID: <20240321195309.484275-1-ubizjak@gmail.com> X-Mailer: git-send-email 2.42.0 Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: quoted-printable Content-Type: text/plain; charset="utf-8" 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. Signed-off-by: Uros Bizjak Cc: Peter Zijlstra Cc: Ingo Molnar Cc: Will Deacon Cc: Waiman Long Cc: Boqun Feng Reviewed-by: Waiman Long --- 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 ebe6b8ec7cb3..1df5fef8a656 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 */ --=20 2.42.0