From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from mail-wm1-f51.google.com (mail-wm1-f51.google.com [209.85.128.51]) (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 7269034F279 for ; Fri, 6 Mar 2026 22:51:57 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=209.85.128.51 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1772837518; cv=none; b=nCAauxHpswk0IVZ2l2e9GcLtBpmhxvaFtiQSIDMkijo0qqyKGWYNn5Jn0Y1suInmOvQQ3bF14FDuC6Ui0mzEeV26XzJQzCMdI0MgSO0GRsgyzhoOiI6+3gPEyKXxzeisIF/RRNQIUHiF6i0LfRki9hsXN9Q+0NxE0+dmYdz1TdE= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1772837518; c=relaxed/simple; bh=tx+j7JVVMzme9A8nZVX+nxHi38OaZRMPAgTMYNrU8ZE=; h=From:To:Cc:Subject:Date:Message-Id:In-Reply-To:References: MIME-Version; b=FvWYWW1spzujiRpMEKViYHK3NRWYPTJGwRpuwMKlaypvsOjaURmeZh/T2jEyfRG1NSsQaCmIGjkn/c+JANR23oe3WAunj5BYjWtX7rZdbJ9cNWophQ5rQUp9I+J/W2gznvwhozo4ZP+C5LQBkrXm03dzbzPLdE4Pegx9XcP9iUU= 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=M8K+PrkD; arc=none smtp.client-ip=209.85.128.51 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="M8K+PrkD" Received: by mail-wm1-f51.google.com with SMTP id 5b1f17b1804b1-4852a9c6309so5234045e9.0 for ; Fri, 06 Mar 2026 14:51:57 -0800 (PST) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=gmail.com; s=20230601; t=1772837516; x=1773442316; darn=vger.kernel.org; h=content-transfer-encoding:mime-version:references:in-reply-to :message-id:date:subject:cc:to:from:from:to:cc:subject:date :message-id:reply-to; bh=dYRb/0buUb3p9AxqkSCYQnLtLdpN/kPE8ow1mG/Cv8E=; b=M8K+PrkDZ9rRmaC5Qj5DM0EmW/KmomrYpY+S6QqIcS0/FMA/jAyey+K5ruulaz6vng A8Xs789IdxZqgl5m/ggTKJHAqp/DisbPWtXqqwoXjUiypOetmoUeZ4sMWjl48UvcS+ro 8hAnGuFkBqDfkEvNWdf74GwJq9o/Jm0QtA/Btd0Isx0WZslghLxXVP/YIZx6ra5kZUIn jhViKs+oSOwDJqDlGj4zwsYV1ii0phGm5EfjG3jM3TNJCEY2N5VANZJ+FDgcx8Wmz+0m tQQBDkKKOniTUKqxdLMwwT9p7kCCVdDS4qaD3DR//QHcclSTY3ban64y0R7Odsfk6Lxv /ueA== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20230601; t=1772837516; x=1773442316; h=content-transfer-encoding:mime-version:references:in-reply-to :message-id:date:subject:cc:to:from:x-gm-gg:x-gm-message-state:from :to:cc:subject:date:message-id:reply-to; bh=dYRb/0buUb3p9AxqkSCYQnLtLdpN/kPE8ow1mG/Cv8E=; b=lENTVKBV27wi12kdOkPSBdRl8ONCSPaqkr5gQIghSR5+3VLPeMwLXjwfMqdyfc6Cst xGNtAVxlnaJK1FH16SamyB8UPAJdlSQ0T6ORF8GgloD43MtZSlgl8ToQBC1ckpqzNxi4 maDZ+SgDmQYeBw+XKuKdYDd8pyGfcv6EwPkVeUKLkQggW/AzGJjzTt6lXGT04KLTxmYt PYMQwVUvstBFfa592nfjN60uFPmldxaR8kwvq1quh86viFAvMp+0k9T9V5QdoqCZfwqy wc9Az96Nke1XM3ggdeiMowuDlyjUm6/ytd1Xfsf57pnXQ6S7Fkn3l9DCiIm3iGFAKFrd 0EVA== X-Forwarded-Encrypted: i=1; AJvYcCV7Rv8TChh3X+lUqwNmZMeC4YXyxJk/WrBrzEaMGUw7hjkjXRH3q/hI03MEOKScAl5z4WYeUSCyaZP3ppE=@vger.kernel.org X-Gm-Message-State: AOJu0Yzn/MDZBBzyhemB7gZFOgP9b87pvTy6rkcyjVlTZKfVI1gbuWXY JE8uiCfBthGBEXGKGqkhebRfN2DhZGq2MUoe93XITQTBsx+Iq9PSi/Jp X-Gm-Gg: ATEYQzzs9gmezKkZgj+9NtfMgIKJ3jbdFQ1VN5IxW3kvaatK6D0PgbDsGFG0Q/EJngV lrV5YD/tdFMJ7koC/ltX3XoU7yrHfDSYZf9CRf6/jwOgh5x5V7PTTy7xl1xvaE7mSvn+RBlPW8O 3WDXPsyuRZY17zLoCcPRJnQ5a8r1hSPW94Mv2sXR0Wj6aXBOLY5I3OyLl8vE++C/+xdkC71ioYm jdRAjHLqntfOTptmXvwdyHnzp/V12bUoVwLoiNHhKdWfdcRgFMTeTIyYWQIHtV7uI8QICRSBxDl RZOhjpz7koHxg5zb0l4C8t2hpnH82WD0NtW1QuhTDykylEcSYXPPHyZuTa5Evfc/OVgR0OUC46k 7FJijsTZ3drjUx47nAjo2/i5ttvd0CbeajeZFMMwv3P2C7oqGEpYPZA9YmUMjzK2/sHfzvO0XFU 6rovZoPMuEVFkps8R8L7HDSkUzqm44qxHV+DnbOo9SwXARWW+NtuB/WKzkPuv1Ys5Fr//ZclvSu N41zlZqpjIt X-Received: by 2002:a05:600c:c05a:b0:483:129e:b573 with SMTP id 5b1f17b1804b1-4852696b8d7mr49188385e9.18.1772837515834; Fri, 06 Mar 2026 14:51:55 -0800 (PST) Received: from snowdrop.snailnet.com (82-69-66-36.dsl.in-addr.zen.co.uk. [82.69.66.36]) by smtp.gmail.com with ESMTPSA id ffacd0b85a97d-439dae57c05sm6160845f8f.39.2026.03.06.14.51.55 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Fri, 06 Mar 2026 14:51:55 -0800 (PST) From: david.laight.linux@gmail.com To: Waiman Long , Peter Zijlstra , Ingo Molnar , Will Deacon , Boqun Feng , linux-kernel@vger.kernel.org, Linus Torvalds , Yafang Shao , Steven Rostedt Cc: David Laight Subject: [PATCH v3 next 2/5] Optimise vcpu_is_preempted() check Date: Fri, 6 Mar 2026 22:51:47 +0000 Message-Id: <20260306225150.93178-3-david.laight.linux@gmail.com> X-Mailer: git-send-email 2.39.5 In-Reply-To: <20260306225150.93178-1-david.laight.linux@gmail.com> References: <20260306225150.93178-1-david.laight.linux@gmail.com> Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: 8bit From: David Laight The vcpu_is_preempted() test stops osq_lock() spinning if a virtual CPU is no longer running. Although patched out for bare-metal, the code still needs the CPU number. Reading this from 'prev->cpu' is a pretty much guaranteed have a cache miss when osq_unlock() is waking up the next cpu. Instead save 'prev->cpu' in 'node->prev_cpu' and use that value instead. Update in the osq_lock() 'unqueue' path when 'node->prev' is changed. Signed-off-by: David Laight --- kernel/locking/osq_lock.c | 9 ++++++--- 1 file changed, 6 insertions(+), 3 deletions(-) diff --git a/kernel/locking/osq_lock.c b/kernel/locking/osq_lock.c index 96c6094157b5..0e1c7d11b6c0 100644 --- a/kernel/locking/osq_lock.c +++ b/kernel/locking/osq_lock.c @@ -16,6 +16,7 @@ struct optimistic_spin_node { struct optimistic_spin_node *next, *prev; int locked; /* 1 if lock acquired */ int cpu; /* encoded CPU # + 1 value */ + int prev_cpu; /* encoded CPU # + 1 value */ }; static DEFINE_PER_CPU_SHARED_ALIGNED(struct optimistic_spin_node, osq_node); @@ -29,9 +30,9 @@ static inline int encode_cpu(int cpu_nr) return cpu_nr + 1; } -static inline int node_cpu(struct optimistic_spin_node *node) +static inline int prev_cpu_nr(struct optimistic_spin_node *node) { - return node->cpu - 1; + return READ_ONCE(node->prev_cpu) - 1; } static inline struct optimistic_spin_node *decode_cpu(int encoded_cpu_val) @@ -110,6 +111,7 @@ bool osq_lock(struct optimistic_spin_queue *lock) if (old == OSQ_UNLOCKED_VAL) return true; + WRITE_ONCE(node->prev_cpu, old); prev = decode_cpu(old); node->prev = prev; node->locked = 0; @@ -144,7 +146,7 @@ bool osq_lock(struct optimistic_spin_queue *lock) * polling, be careful. */ if (smp_cond_load_relaxed(&node->locked, VAL || need_resched() || - vcpu_is_preempted(node_cpu(node->prev)))) + vcpu_is_preempted(prev_cpu_nr(node)))) return true; /* unqueue */ @@ -201,6 +203,7 @@ bool osq_lock(struct optimistic_spin_queue *lock) * it will wait in Step-A. */ + WRITE_ONCE(next->prev_cpu, prev->cpu); WRITE_ONCE(next->prev, prev); WRITE_ONCE(prev->next, next); -- 2.39.5