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Mon, 6 Feb 2023 10:42:46 +0100 (CET) Received: from localhost (localhost [127.0.0.1]) by gentwo.de (Postfix) with ESMTP id 14D5DB00100; Mon, 6 Feb 2023 10:42:46 +0100 (CET) Date: Mon, 6 Feb 2023 10:42:46 +0100 (CET) From: Christoph Lameter To: Marcelo Tosatti cc: Aaron Tomlin , Frederic Weisbecker , Andrew Morton , linux-kernel@vger.kernel.org, linux-mm@kvack.org Subject: Re: [PATCH 3/5] mm/vmstat: use cmpxchg loop in cpu_vm_stats_fold In-Reply-To: Message-ID: <47a289f0-ae96-e0e6-c579-70ec61fff384@gentwo.de> References: <20230201195013.881721887@redhat.com> <20230201195104.460373427@redhat.com> <5615572-974e-74cc-6c34-1de618b777cf@gentwo.de> MIME-Version: 1.0 Content-Type: text/plain; charset=US-ASCII X-Rspam-User: X-Rspamd-Server: rspam04 X-Rspamd-Queue-Id: A4296100002 X-Stat-Signature: jrgmkgay4kpmkth6a9tgqpmfr9uaacdw X-HE-Tag: 1675676568-45290 X-HE-Meta: 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 BumnZZcQ 61RNqz0mw9MYMKWU9WxmujO5pnW6Xp5K7ODrGKo8W5xhwp2oEk5tA28pUwg8HnGstZBhK9V+MCgtko7BL64gW5etRNI5bw9FCVR9AOskduL1DBSmuEJZwIBDOwqH0OgMkhbrBo7EkqrzRQOl5Q2kjYS99mD8i3K3ZdvpqFhaDGOwf0cCTDKX60QRoRSK3jjykwa5+r+eQZk4vwakLPptdnoMQN40p8c8Z9xcO X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: On Fri, 3 Feb 2023, Marcelo Tosatti wrote: > > Isnt there some lock/serializtion to stall the kernel until you are done? > > Not that i know of. Anyway, an additional datapoint is: > > "Software defined PLC" > (https://www.redhat.com/en/blog/software-defined-programmable-logic-controller-introduction), > applications > can perform system calls in their time sensitive loop. > > One example of an opensource software is OpenPLC. > > One would like to avoid interruptions for those cases as well. Well allowing sytem calls during "time sensitiveness" implies it is not that sensitive to vmstat updates which have a smaller impact than system calls. Unless we are talking about virtual system calls like gettimeofday or clock_gettime. These do not enter the kernel if configured correctly.