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[92.21.58.28]) by smtp.gmail.com with ESMTPSA id ffacd0b85a97d-3b471b975efsm12453659f8f.46.2025.07.08.04.00.18 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Tue, 08 Jul 2025 04:00:18 -0700 (PDT) Date: Tue, 8 Jul 2025 12:00:16 +0100 From: David Laight To: Oleg Nesterov Cc: Steven Rostedt , "Li,Rongqing" , Peter Zijlstra , "linux-kernel@vger.kernel.org" , "vschneid@redhat.com" , "mgorman@suse.de" , "bsegall@google.com" , "dietmar.eggemann@arm.com" , "vincent.guittot@linaro.org" , "juri.lelli@redhat.com" , "mingo@redhat.com" Subject: Re: divide error in x86 and cputime Message-ID: <20250708120016.4071595d@pumpkin> In-Reply-To: <20250707230057.GC15787@redhat.com> References: <78a0d7bb20504c0884d474868eccd858@baidu.com> <20250707220937.GA15787@redhat.com> <20250707182056.66a8468a@gandalf.local.home> <20250707183331.029570bf@gandalf.local.home> <20250707230057.GC15787@redhat.com> X-Mailer: Claws Mail 4.1.1 (GTK 3.24.38; arm-unknown-linux-gnueabihf) 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=US-ASCII Content-Transfer-Encoding: 7bit On Tue, 8 Jul 2025 01:00:57 +0200 Oleg Nesterov wrote: > On 07/07, Steven Rostedt wrote: > > > > On Mon, 7 Jul 2025 18:20:56 -0400 > > Steven Rostedt wrote: > > > > > I would say this should never happen and if it does, let the kernel crash. > > > > >> [78250815.703852] CPU: 127 PID: 83435 Comm: killall Kdump: loaded Tainted: P OE K 5.10.0 #1 > > > > This happened on a 5.10 kernel with a proprietary module loaded, so > > honestly, if it can't be reproduced on a newer kernel without any > > proprietary modules loaded, I say we don't worry about it. > > Yes, agreed, see my reply to myself. Except that just isn't relevant. The problem is that the process running time (across all threads) can easily exceed 2^64 nanoseconds. With cpu having more and more 'cores' and software spinning to reduce latency it will get more and more common. Perhaps standardising on ns for timers (etc) wasn't such a bright idea. Maybe 100ns would have been better. But the process 'rtime' does need dividing down somewhat. Thread 'rtime' is fine - 564 years isn't going to be out problem! David