As reported in the community forum [0][1], QEMU processes for Linux
guests would consume more CPU on the host after an update to QEMU 9.2.
The issue was reproduced and bisecting pointed to QEMU commit
f0ccf77078 ("hpet: fix and cleanup persistence of interrupt status").
Some quick experimentation suggests that in particular the last part
is responsible for the issue:
> - the timer must be kept running even if not enabled, in
> order to set the ISR flag, so writes to HPET_TN_CFG must
> not call hpet_del_timer()
Users confirmed that setting the hpet=off machine flag works around
the issue[0]. For Windows (7 or later) guests, the flag is already
disabled, because of issues in the past [2].
Upstream suggested reverting the relevant patches for now [3], because
other issues were reported too. All except commit 5895879aca ("hpet:
remove unnecessary variable "index"") are actually dependent on each
other for cleanly reverting f0ccf77078, and while not strictly
required, that one was reverted too for completeness.
[0]: https://forum.proxmox.com/threads/163694/
[1]: https://forum.proxmox.com/threads/161849/post-756793
[2]: https://lists.proxmox.com/pipermail/pve-devel/2012-December/004958.html
[3]: https://lore.kernel.org/qemu-devel/CABgObfaKJ5NFVKmYLFmu4C0iZZLJJtcWksLCzyA0tBoz0koZ4A@mail.gmail.com/
Signed-off-by: Fiona Ebner <f.ebner@proxmox.com>
