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Thu, 22 Oct 2026 14:09:43 -0700 (PDT) X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Post: List-Help: List-Subscribe: List-Unsubscribe: List-Owner: Precedence: list MIME-Version: 1.0 References: <20261001202134.33929-1-dwmw2@infradead.org> <20261001202134.33929-5-dwmw2@infradead.org> In-Reply-To: <20261001202134.33929-5-dwmw2@infradead.org> From: John Stultz Date: Thu, 22 Oct 2026 14:09:31 -0700 X-Gm-Features: AclHuK_PmPEE0hBLIrheAqDBeCPQG2A9gzjeDHX2Ls_ohRpLNTKpvF1eJqvzhug Message-ID: Subject: Re: [PATCH 4/5] timekeeping: Reinstate proportional correction of ntp_error To: David Woodhouse Cc: Thomas Gleixner , Stephen Boyd , Miroslav Lichvar , Rodolfo Giometti , Ryan Luu , Julien Ridoux , linux-kernel@vger.kernel.org, David Woodhouse Content-Type: text/plain; charset="UTF-8" Content-Transfer-Encoding: quoted-printable On Thu, Oct 1, 2026 at 1:21=E2=80=AFPM David Woodhouse wrote: > > From: David Woodhouse > > The =C2=B11 mult dithering is sufficient to keep ntp_error at zero once > it's already there, but it doesn't do much to reduce it once any > significant ntp_error has accumulated (e.g. from frequency or phase > adjustments) =E2=80=94 it can typically only drain single-digit nanosecon= ds > per second. Commit dc491596f639 ("timekeeping: Rework frequency > adjustments to work better w/ nohz") removed a larger skew because in > a tickless kernel, it would remain in effect for a full idle period > and overshoot. Now that timekeeping_max_deferment() ensures that the > system wakes at the top of the second when skew is active, the > correction can be reinstated. If ntp_error exceeds an amount that a > single =C2=B11 change to mult can drain within a minute, add an > additional bias to mult to close the gap. > > Signed-off-by: David Woodhouse > Assisted-by: LLM I can't say I've totally wrapped my head around all the details in this one, but at a high level it sounds reasonable and nothing is obviously sticking out to me. Acked-by: John Stultz