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[0/2] control guest time using a dilation factor

Message ID 20250610212829.2818792-1-pierrick.bouvier@linaro.org
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Series control guest time using a dilation factor | expand

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Pierrick Bouvier June 10, 2025, 9:28 p.m. UTC 
Depending on host cpu speed, and QEMU optimization level, it may sometimes be
needed to slow or accelerate time guest is perceiving. A common scenario is
hitting a timeout during a boot process, because some operations were not
finished on time.

An existing solution for that is -icount shift=X, with low values, which will
roughly map virtual time to how many instructions were executed.

This series introduces another approach, based on faking host time returned to
the guest, by applying a time-dilation factor. Time will go slower/faster for
the guest, without impacting QEMU emulation speed.

It may eventually be used to fix some of the timeouts we hit in CI, by slowing
down time in VM, to be less sensitive to varying cpu performance.

Pierrick Bouvier (2):
  qemu/timer: introduce time dilation factor
  system/rtc: introduce -rtc time-dilation option

 include/qemu/timer.h     | 22 ++++++++++++++++------
 system/rtc.c             | 11 +++++++++++
 system/vl.c              |  3 +++
 util/qemu-timer-common.c |  1 +
 qemu-options.hx          |  7 ++++++-
 5 files changed, 37 insertions(+), 7 deletions(-)