From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from mail-pl1-f172.google.com (mail-pl1-f172.google.com [209.85.214.172]) (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 4D969225A59 for ; Tue, 12 Aug 2025 08:25:41 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=209.85.214.172 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1754987142; cv=none; b=Y/DcRj6gjspJU7YtnHe74/uJFeSWzLRhJrb/jPXS3xWlKHAZ7K2my9GElLcofqRyrTm5j7enlFsIiMwHVNR47bKAoE4DJX8/bVAgq/65CNan/4mh//yiVCWGSyG3MHsv23I1ZQIdRVdSqyH6yb3jQQL03VBBiZ+TjyTcUndc2+0= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1754987142; c=relaxed/simple; bh=js32FIpA4GruiS49feA+nh/fpXBlFmHkE39lG/5Fikc=; h=From:To:Cc:Subject:Date:Message-Id:MIME-Version:Content-Type; b=S7jf850JHE9BB2E2zvzNhwZ93szJpB61rJ9XPDYUxuyM7Vu+Ez2HOM1im8wrVmN/HanmT97tkyUBxO5h8t0L45ztTzuYfzJi0WYS9UlFOxUrOxLRsZdyjTY+7ED5B1SooSfDWkedMnHE61CuUyrshxwYkfVGMYdaE420GJx+r58= 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=U4eOCV/H; arc=none smtp.client-ip=209.85.214.172 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="U4eOCV/H" Received: by mail-pl1-f172.google.com with SMTP id d9443c01a7336-2400f746440so43261405ad.2 for ; Tue, 12 Aug 2025 01:25:40 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=gmail.com; s=20230601; t=1754987140; x=1755591940; 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=VBKTouzb9zVyT0NEzPET84Kjpud/5/zvHGbDZ3mAKJI=; b=U4eOCV/HQEJ6A9kQkFmCoojDKIN1+WjbUzKkI5KYhkjX1YUQfLWjEgDJ5zpwhMo+FN oeY0wZpSj2jNivaAbLdPN5nKviRMzpuSbybE8JAjN6tZNDIHt9YFbTX2PLx48Cln1nFX TpB5A/yVXTJoZC5e2I3zPW990lVsY/OSJHJzu8qOav6QSB4MtjY0kb5H0MMK7/PeIpWK uJx4pz8oKGRdTVdZGS1SpfOdp9wOCF4uV2yNjA5TcAW2iPGeAdKuQ10a/VnRPPfl1tI2 UqwjJZDY91a3UyYW5HleRbvMnYK8eG54IuGpj507aZ3JvaoBxsIz5b/1cqgUYKrUcNqY GtCw== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20230601; t=1754987140; x=1755591940; 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=VBKTouzb9zVyT0NEzPET84Kjpud/5/zvHGbDZ3mAKJI=; b=fxFlMDlpcmm1+gIyythb+xwcLXKAOfcXP3G6dKKScmCcjqOXJdXBhpglEzM49coG6v vq7g0L3YlMM+AuOcvzZbpquMhNItnvr2yzP44cNztpsEjgJERJn88d+jE3zGsKeCbU9J c0kgn1KeuHpDoHS8Duou7ITdqbVUQaPL/i79a37gp98cknlUjXFlQpqfjRjYwu2Xp7M7 5UKn4lNhY38D1HVGlM1l/NpGGsUzb1VTPSFFECntxyR5RS1RLC1uayuxscZjpKpVdh5C cRrkxtbNqOwQCRqbff+++3g4ptjTk5tcRdXXbq/Fvt6/Ic+9dRF3/nX1aTzswh41GFoI 7x8Q== X-Forwarded-Encrypted: i=1; AJvYcCUFawGlMe8WS7BZnuYhlMbium/lCTB4ZDBACnCGgmkSarSrp1YaM4BmWGxVp4p8UvLAD/aBGQj56W8BRBY=@vger.kernel.org X-Gm-Message-State: AOJu0YxIticI433sEa+T0OsC/sblzZk2A/YGZ83VrAeFNruaCCLmnIyh f3+usJaJTb4ZdyaWXji3uKk6bibtQ8QyRBFu014PGl87G6aWzYRSRlAf X-Gm-Gg: ASbGncus7oj1x40DQKbfUBs9LIS60WuEqmjf2V/8esTPP2oJ90FSPgGdcQUCKrqqQxR lb5v2u0v9UIuJXbB/uL4I8wivMmikfwjkye52UX90IhjE3PjWv339sQEGXbbjZqqZQuV8Z5A1Lw hUB/yTc7fD7JEIN+z1HA2+W88GyJrLyq3vJs8vSetNTrwKPLf92ZDCNTVtORw7gRdT9XU3O0TKU fThzZmcu1fOx5E8sMt/oSIGHALQdDtRYcc8i9+WjUi+NvLvvc70vbdy+eC4T5K25bvQn/ZE6KXj l4HVck2Qjw0DvY97CrysZUB1Gpm6bpN3jp6wAIIDpOboNpl8fXemgsjUyIot8Qq1moR+7vzu+uz EXlKATn7PVV7M0Y/Se1MErc6hYI9K X-Google-Smtp-Source: AGHT+IHBcRypzsJ0IagOxKFTQrLT1bEYvZZnDiiqpkXRrlmnr/Wgdh/YYe8EgX02o6YmyTpFoabqGg== X-Received: by 2002:a17:902:c943:b0:243:8f:6d7d with SMTP id d9443c01a7336-243008f9b18mr17751435ad.50.1754987140390; Tue, 12 Aug 2025 01:25:40 -0700 (PDT) Received: from localhost.localdomain ([152.32.169.72]) by smtp.gmail.com with ESMTPSA id d9443c01a7336-242bc894dc8sm110692525ad.72.2025.08.12.01.25.37 (version=TLS1_3 cipher=TLS_CHACHA20_POLY1305_SHA256 bits=256/256); Tue, 12 Aug 2025 01:25:39 -0700 (PDT) From: yaozhenguo X-Google-Original-From: yaozhenguo To: tglx@linutronix.de, yaoma@linux.alibaba.com, akpm@linux-foundation.org Cc: max.kellermann@ionos.com, lihuafei1@huawei.com, yaozhenguo@jd.com, linux-kernel@vger.kernel.org, ZhenguoYao Subject: [PATCH] watchdog/softlockup:Fix incorrect CPU utilization output during softlockup Date: Tue, 12 Aug 2025 16:25:10 +0800 Message-Id: <20250812082510.32291-1-yaozhenguo@jd.com> X-Mailer: git-send-email 2.39.3 (Apple Git-146) Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit From: ZhenguoYao Since we use 16-bit precision, the raw data will undergo integer division, which may sometimes result in data loss. This can lead to slightly inaccurate CPU utilization calculations. Under normal circumstances, this isn’t an issue. However, when CPU utilization reaches 100%, the calculated result might exceed 100%. For example, with raw data like the following: sample_period 400000134 new_stat 83648414036 old_stat 83247417494 sample_period=400000134/2^24=23 new_stat=83648414036/2^24=4985 old_stat=83247417494/2^24=4961 util=105% Below log will output： CPU#3 Utilization every 0s during lockup: #1: 0% system, 0% softirq, 105% hardirq, 0% idle #2: 0% system, 0% softirq, 105% hardirq, 0% idle #3: 0% system, 0% softirq, 100% hardirq, 0% idle #4: 0% system, 0% softirq, 105% hardirq, 0% idle #5: 0% system, 0% softirq, 105% hardirq, 0% idle To avoid confusion, we enforce a 100% display cap when calculations exceed this threshold. Signed-off-by: ZhenguoYao --- kernel/watchdog.c | 7 +++++++ 1 file changed, 7 insertions(+) diff --git a/kernel/watchdog.c b/kernel/watchdog.c index 9c7134f7d2c4..29787996c69c 100644 --- a/kernel/watchdog.c +++ b/kernel/watchdog.c @@ -444,6 +444,13 @@ static void update_cpustat(void) old_stat = __this_cpu_read(cpustat_old[i]); new_stat = get_16bit_precision(cpustat[tracked_stats[i]]); util = DIV_ROUND_UP(100 * (new_stat - old_stat), sample_period_16); + /* Since we use 16-bit precision, the raw data will undergo + * integer division, which may sometimes result in data loss, + * and then result might exceed 100%. To avoid confusion, + * we enforce a 100% display cap when calculations exceed this threshold. + */ + if (util > 100) + util = 100; __this_cpu_write(cpustat_util[tail][i], util); __this_cpu_write(cpustat_old[i], new_stat); } -- 2.43.5