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+
+-icount,sleep=off mode is broken (target slows down or hangs)
+
+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 booting stage).
+Example scenarios I've described here: http://lists.nongnu.org/archive/html/qemu-discuss/2018-08/msg00102.html
+
+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 <email address hidden>
+
+  Signed-off-by: Pavel Dovgalyuk <email address hidden>
+  Message-Id: <20160310115603.4812.67559.stgit@PASHA-ISP>
+  Signed-off-by: Paolo Bonzini <email 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(...)" line.
+
+I'm sure following bugs are just particular cases of the issue: #1774677, #1653063 .
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