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Fri, 11 Sep 2026 18:02:57 +0000 Received: from dip56.lsn.sg3.yahoo.com ([106.10.223.65]) by hello (SMTP) with SMTP ID 19a1cc9871ef7e33e3b462ec7ba43344; Fri, 11 Sep 2026 18:02:53 +0000 (UTC) Date: Fri, 11 Sep 2026 23:32:52 +0530 Message-ID: <1789149772593550955.2470305@yahoo.com> From: "A Kundu" To: , Subject: TSC marked unstable on AMD Zen4 (Ryzen 7 250, ThinkBook 16 G9 AHP): 15.6G-cycle warp CPU0->CPU2 at boot, 7.1.12 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="utf-8" Content-Transfer-Encoding: quoted-printable References: <1789149772593550955.2470305.ref@yahoo.com> X-Mailer: WebService/1.1.26525 mail.core.serving.mcws.prd.acl:role.token.mcws.jsmtp.yahoo Hi, On an AMD Zen4 laptop, kernel 7.1.12 (x86_64) marks the TSC unstable at boot with a massive cross-CPU warp: [ 0.191568] TSC synchronization [CPU#0 -> CPU#2]: [ 0.191571] Measured 15645116622 cycles TSC warp between CPUs, turning o= ff TSC clock. [ 0.191580] tsc: Marking TSC unstable due to check_tsc_sync_source faile= d That is 15,645,116,622 cycles (~4.7 s at the detected 3294 MHz) of skew between CPU0 and CPU2 during early-boot synchronization. The kernel then runs on HPET; the TSC is dropped from the available clocksource list entirely. Hardware: AMD Ryzen 7 250 w/ Radeon 780M (Zen4), single socket, constant_ts= c + nonstop_tsc + rdtscp present. Lenovo ThinkBook 16 G9 AHP (type 21UT), BIOS SQCN20WW dated 2025-11-10 (latest published for this model). Notes: - A previous boot configuration used the `tsc=3Dreliable` parameter, which forced the skewed TSC into service. Applications then observed multi-second backwards jumps of CLOCK_MONOTONIC depending on the CPU they ran on (Chromium renderer CHECK failures; journald boot accounting disorder). The parameter had been masking this boot-time failure. - The warp magnitude =E2=80=94 seconds, not a small calibration drift =E2= =80=94 suggests the secondary CPU's TSC was never synchronized by firmware rather than a measurement issue in check_tsc_sync_source. - Suggest Lenovo/AMD be looked at for the firmware-side sync, but the kernel-side behaviour (boot-time detection working as designed) is reported here for the record since 15.6G cycles is far outside anything a retry would paper over. Full dmesg, CPUID dumps and further data available on request. Happy to test patches. Thanks, Avikalpa Kundu