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[Qemu-devel] [Bug 1790460] Re: -icount, sleep=off mode is broken (target
[Qemu-devel] [Bug 1790460] Re: -icount, sleep=off mode is broken (target slows down or hangs)
Tue, 04 Sep 2018 12:10:40 -0000
This modification also fixes issue:
Although I tested it only on v2.12.0 and didn't noticed performance improvement.
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-icount,sleep=off mode is broken (target slows down or hangs)
Status in QEMU:
QEMU running with options "-icount,sleep=off -rtc clock=vm" doesn't execute
emulation at maximum possible speed.
Target virtual clock may run faster or slower than realtime clock by N times,
where N value depends on various unrelated conditions (i.e. random from the
user point of view). The worst case is when target hangs (hopefully, early in
Example scenarios I've described here:
QEMU process just sleeps most of the time (polling, waiting some
condition, etc.). I've tried to debug issue and came to 99% conclusion
that there are racing somewhere in qemu internals.
The feature is broken since v2.6.0 release.
Bad commit is 281b2201e4e18d5b9a26e1e8d81b62b5581a13be by Pavel Dovgalyuk,
03/10/2016 05:56 PM:
icount: remove obsolete warp call
qemu_clock_warp call in qemu_tcg_wait_io_event function is not needed
anymore, because it is called in every iteration of main_loop_wait.
Reviewed-by: Paolo Bonzini <address@hidden>
Signed-off-by: Pavel Dovgalyuk <address@hidden>
Signed-off-by: Paolo Bonzini <address@hidden>
I've reverted commit to all major releases and latest git master
branch. Issue was fixed for all of them. My adaptation is trivial:
just restoring removed function call before "qemu_cond_wait(...)"
I'm sure following bugs are just particular cases of the issue:
#1774677, #1653063 .
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