Hi Thomas,

On Tue, Feb 24, 2026 at 05:36:49PM +0100, Thomas Gleixner wrote:
> The TSC deadline timer is directly coupled to the TSC and setting the next
> deadline is tedious as the clockevents core code converts the
> CLOCK_MONOTONIC based absolute expiry time to a relative expiry by reading
> the current time from the TSC. It converts that delta to cycles and hands
> the result to lapic_next_deadline(), which then has read to the TSC and add
> the delta to program the timer.
> 
> The core code now supports coupled clock event devices and can provide the
> expiry time in TSC cycles directly without reading the TSC at all.
> 
> This obviouly works only when the TSC is the current clocksource, but
> that's the default for all modern CPUs which implement the TSC deadline
> timer. If the TSC is not the current clocksource (e.g. early boot) then the
> core code falls back to the relative set_next_event() callback as before.
> 
> Signed-off-by: Thomas Gleixner <tglx@kernel.org>
> Cc: x86@kernel.org

After this change landed in -next as commit f246ec3478cf ("x86/apic:
Enable TSC coupled programming mode"), two of my Intel-based test
machines fail to boot. Unfortunately, I do not think I have any serial
access on these, so I have little introspective ability. Is there any
information I can provide or patches I can test to try and help figure
out what is going on here? I have attached the output of lscpu of both
machines, in case there is some common thread there.

Cheers,
Nathan

# bad: [d517cb8cea012f43b069617fc8179b45404f8018] Add linux-next specific files for 20260302
# good: [11439c4635edd669ae435eec308f4ab8a0804808] Linux 7.0-rc2
git bisect start 'd517cb8cea012f43b069617fc8179b45404f8018' '11439c4635edd669ae435eec308f4ab8a0804808'
# good: [30cad5d4db9212a3e9bb99be1d99c4fbc17966c7] Merge branch 'master' of https://git.kernel.org/pub/scm/linux/kernel/git/wpan/wpan-next.git
git bisect good 30cad5d4db9212a3e9bb99be1d99c4fbc17966c7
# good: [5add127981db7fda704fb251de1a3a77e3282e37] Merge branch 'for-next' of https://git.kernel.org/pub/scm/linux/kernel/git/broonie/sound.git
git bisect good 5add127981db7fda704fb251de1a3a77e3282e37
# bad: [49b56e8a6ca8c20f7d9bb8904d4b2a5bf032554a] Merge branch 'char-misc-next' of https://git.kernel.org/pub/scm/linux/kernel/git/gregkh/char-misc.git
git bisect bad 49b56e8a6ca8c20f7d9bb8904d4b2a5bf032554a
# good: [1695e1c2db4247e8428badf667900beec51c5174] Merge branch 'for-next' of https://git.kernel.org/pub/scm/linux/kernel/git/robh/linux.git
git bisect good 1695e1c2db4247e8428badf667900beec51c5174
# bad: [c50f05bd3c4e992c1dfb61b14d6f7d999f1381f9] Merge branch into tip/master: 'sched/hrtick'
git bisect bad c50f05bd3c4e992c1dfb61b14d6f7d999f1381f9
# bad: [343f2f4dc5425107d509d29e26ef59c2053aeaa4] hrtimer: Try to modify timers in place
git bisect bad 343f2f4dc5425107d509d29e26ef59c2053aeaa4
# bad: [6abfc2bd5b0cff70db99a273f2a161e2273eae6d] hrtimer: Use guards where appropriate
git bisect bad 6abfc2bd5b0cff70db99a273f2a161e2273eae6d
# good: [0abec32a6836eca6b61ae81e4829f94abd4647c7] sched/hrtick: Mark hrtick timer LAZY_REARM
git bisect good 0abec32a6836eca6b61ae81e4829f94abd4647c7
# good: [23028286128d817a414eee0c0a2c6cdc57a83e6f] x86/apic: Avoid the PVOPS indirection for the TSC deadline timer
git bisect good 23028286128d817a414eee0c0a2c6cdc57a83e6f
# bad: [f246ec3478cfdab830ee0815209f48923e7ee5e2] x86/apic: Enable TSC coupled programming mode
git bisect bad f246ec3478cfdab830ee0815209f48923e7ee5e2
# good: [89f951a1e8ad781e7ac70eccddab0e0c270485f9] clockevents: Provide support for clocksource coupled comparators
git bisect good 89f951a1e8ad781e7ac70eccddab0e0c270485f9
# first bad commit: [f246ec3478cfdab830ee0815209f48923e7ee5e2] x86/apic: Enable TSC coupled programming mode