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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, Jeff Layton Subject: Re: [PATCH v8 01/11] timekeeping: move multigrain timestamp floor handling into timekeeper In-Reply-To: <87a5g79aag.ffs@tglx> References: <20240914-mgtime-v8-0-5bd872330bed@kernel.org> <20240914-mgtime-v8-1-5bd872330bed@kernel.org> <87a5g79aag.ffs@tglx> Date: Mon, 16 Sep 2024 12:32:43 +0200 Message-ID: <874j6f99dg.ffs@tglx> MIME-Version: 1.0 Content-Type: text/plain X-Rspamd-Server: rspam12 X-Rspamd-Queue-Id: 3085F140005 X-Stat-Signature: ory5yjqs7uhp4ohibkqyb8aazmkr4u7g X-Rspam-User: X-HE-Tag: 1726482765-541025 X-HE-Meta: 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 qNP3nA2p CFHECE/bNbg0z4Q+B8UY0lYhEJPNdrm/VKwKDUqKaVdyWZoFk7kZ32j5/5GLyJBtCIUKJ8VKGFERM1rYCy/QiM2OEh/4zF8rB0p1S190Sf52NIEWK5tniHH6gDjrNqAb5lj9EKaZ+CW/PgH/dMvtqZ9yi0w== 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 12:12, Thomas Gleixner wrote: > On Sat, Sep 14 2024 at 13:07, Jeff Layton wrote: >> + do { >> + seq = read_seqcount_begin(&tk_core.seq); >> + >> + ts->tv_sec = tk->xtime_sec; >> + mono = tk->tkr_mono.base; >> + nsecs = timekeeping_get_ns(&tk->tkr_mono); >> + offset = *offsets[TK_OFFS_REAL]; >> + } while (read_seqcount_retry(&tk_core.seq, seq)); >> + >> + mono = ktime_add_ns(mono, nsecs); >> + >> + if (atomic64_try_cmpxchg(&mg_floor, &old, mono)) { >> + ts->tv_nsec = 0; >> + timespec64_add_ns(ts, nsecs); >> + } else { >> + /* >> + * Something has changed mg_floor since "old" was >> + * fetched. "old" has now been updated with the >> + * current value of mg_floor, so use that to return >> + * the current coarse floor value. > > '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? Thanks, tglx