Public bug reported:
Hardware: Apple MacBookAir5,2 (mid 2012), Intel Core i5-3427U (Ivy Bridge,
family 6 model 0x3a stepping 9),
firmware 429.0.0.0.0 (03/18/2022), microcode revision 0x21.
OS: Zorin OS 18 (Ubuntu 24.04 "noble" base), stock Ubuntu HWE kernels from the
Ubuntu archive.
Kernel command line: "ro quiet splash vt.handoff=7" (no extra parameters).
Suspend mode: deep (S3).
Symptom:
After opening the lid, the screen stays black for roughly 15-45 seconds. The
delay is entirely in the
kernel resume path: during "Enabling non-boot CPUs", bringing up CPU1 takes
10-45 seconds. While waiting,
the boot CPU appears to run extremely slowly ("perf: interrupt took too long",
"psi_avgs_work hogged CPU
for >10000us", "hrtimer: interrupt took ~2 ms"). CPU2 and CPU3 then come up
quickly; the rest of the
resume is normal.
Regression range / comparison (measured from journal, "Low-level resume
complete" -> "PM: suspend exit"):
7.0.0-28.28~24.04.1 slow 7-28 s (5 resumes)
7.0.0-30.30~24.04.1 slow 7-45 s (16 resumes)
7.0.0-31.31~24.04.1 FAST 0.48-0.75 s (19 resumes after cold boot, 18
Sep - 9 Oct)
(one session right after installing it, started
via warm reboot,
was slow-ish, 3-33 s)
7.0.0-38.38~24.04.4 slow 11-39 s (5 resumes, both after warm reboot and
after cold boot)
Direct A/B test on 10 Oct 2026, both after a cold boot, same machine, same
userspace:
7.0.0-38: resume 15.85 s, of which CPU1 bring-up 14.49 s
7.0.0-31: resume 0.67 s, of which CPU1 bring-up 0.03 s
So 7.0.0-31 does not show the problem, while the kernels before and after it
do. Something in
7.0.0-31 avoids the stall; it would be useful to know what changed between -30
-> -31 and -31 -> -38
in the x86 smpboot / CPU hotplug / MTRR-PAT / resume code.
Possibly related: the long-known slow AP bring-up on S3 resume on Intel Macs,
attributed to
MTRR/PAT state left by the firmware (LKML, Dec 2016, "[PATCH DEBUG] x86,
pat/mtrr: MTRR/PAT init
earlier for each APs", confirmed on MacBookPro9,1).
Attached: dmesg excerpt of one slow resume (7.0.0-38) and one fast
resume (7.0.0-31).
Happy to test kernels or collect more data.
** Affects: linux-hwe-7.0 (Ubuntu)
Importance: Undecided
Status: New
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https://bugs.launchpad.net/bugs/2170448
Title:
Slow S3 resume (10-45 s black screen) on MacBookAir5,2: secondary CPU
bring-up stalls; 7.0.0-31 unaffected, 7.0.0-28/-30/-38 affected
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