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Wong" , Theodore Ts'o , Andreas Dilger , Chris Mason , Josef Bacik , David Sterba , Hugh Dickins , Andrew Morton , Chuck Lever , Vadim Fedorenko Cc: Randy Dunlap , linux-kernel@vger.kernel.org, linux-fsdevel@vger.kernel.org, linux-trace-kernel@vger.kernel.org, linux-doc@vger.kernel.org, linux-xfs@vger.kernel.org, linux-ext4@vger.kernel.org, linux-btrfs@vger.kernel.org, linux-nfs@vger.kernel.org, linux-mm@kvack.org Subject: Re: [PATCH v8 01/11] timekeeping: move multigrain timestamp floor handling into timekeeper In-Reply-To: References: <20240914-mgtime-v8-0-5bd872330bed@kernel.org> <20240914-mgtime-v8-1-5bd872330bed@kernel.org> <87a5g79aag.ffs@tglx> <874j6f99dg.ffs@tglx> Date: Mon, 30 Sep 2024 21:16:07 +0200 Message-ID: <878qv90x6w.ffs@tglx> MIME-Version: 1.0 Content-Type: text/plain X-Rspam-User: X-Rspamd-Server: rspam04 X-Rspamd-Queue-Id: B48C41C0018 X-Stat-Signature: ddteizpd74bs58waaqryp11xrs3gz6ri X-HE-Tag: 1727723770-260089 X-HE-Meta: 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 nw+ts0qs PwLl1/0CPAOzRjRsWucmJH1Wq0hiyav+TlFICCwWJkrBQkgRSt1qJM3r5aBKdtnbPSK9pQ2iE1TkkkN1yZZ1roiSsgy6Xz0GWF5agmATyWxShFuHZmhG7bY7chinbI9VQ+4AGW2dEKFpLp4QJa3v0zALqf6RRtas9lvtN 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: List-Subscribe: List-Unsubscribe: On Mon, Sep 16 2024 at 06:57, Jeff Layton wrote: > On Mon, 2024-09-16 at 12:32 +0200, Thomas Gleixner wrote: >> > 'Something has changed' is a truly understandable technical >> > explanation. >> >> old = mg_floor >> mono = T1; >> mg_floor = mono >> preemption >> >> do { >> mono = T2; >> } >> >> cmpxchg fails and the function returns a value based on T1 >> >> No? >> >> > > Packing for LPC, so I can't respond to all of these just now, but I > will later. You're correct, but either outcome is OK. > > The requirement is that we don't hand out any values that were below > the floor at the time that the task entered the kernel. Since the time > changed while the task was already inside the kernel, either T1 or T2 > would be valid timestamps. That really needs to be documented. A similar scenario exists vs. ktime_get_coarse_real_ts64_mg(). Thanks, tglx