[Qemu-devel] [RFC PATCH V4 0/6] icount: Implement delay algorithm between guest and host clocks

[Sebastian Tanase]

The icount option already implemented in QEMU allows the guest to run at a 
theoretical
frequency of 1/(2^N) GHz (N is the icount parameter). The goal of this patch is 
to have a
real guest frequency close to the one imposed by using the icount option.

The main idea behind the algorithm is that we compare the virtual monotonic 
clock and the
host monotonic clock. For big icounts (on our test machine, an i5 CPU @ 
3.10GHz, icounts
starting at 6) the guest clock will be ahead of the host clock. In this case, 
we try to
sleep QEMU for the difference between the 2 clocks. Therefore, the guest would 
have
executed for a period almost equally to the one imposed by icount. We should 
point out
that the algorithm works only for those icounts that allow the guest clock to 
be in front
of the host clock.

The first patch adds support for QemuOpts for the 'icount' parameter. It also 
adds a
suboption called 'shift' that will hold the value for 'icount'. Therefore we 
now have
-icount shift=N|auto or -icount N|auto.

The second patch adds the 'align' suboption for icount.

The third patch exports 'icount_time_shift' so that it can be used in places 
other than
cpus.c; we need it in cpu-exec.c for calculating for how long we want QEMU to 
sleep.

The forth patch implements the algorithm used for calculating the delay we want 
to sleep.
It uses the number of instructions executed by the virtual cpu and also 
'icount_time_shift'.

The fifth patch prints to the console whenever the guest clock runs behind the 
host
clock. The fastest printing speed is every 2 seconds, and we only print if the 
align option
is enabled. We also have a limit to 100 printed messages.

The sixth patch adds information about the difference between the host and 
guest clocks
(taking into account the offset) in the 'info jit' command. We also print the 
maximum
delay and advance of the guest clock compared to the host clock.

v3 -> v4

* Add better error handling for 'strtol' in patch 2
* Add 'Sleep' instead of 'nanosleep' for Windows hosts in patch 4
* Remove function pointers from patches 4 and 5

Sebastian Tanase (6):
  icount: Add QemuOpts for icount
  icount: Add align option to icount
  icount: Make icount_time_shift available everywhere
  cpu_exec: Add sleeping algorithm
  cpu_exec: Print to console if the guest is late
  monitor: Add drift info to 'info jit'

 cpu-exec.c            | 135 ++++++++++++++++++++++++++++++++++++++++++++++++++
 cpus.c                |  44 ++++++++++++++--
 include/qemu-common.h |  10 +++-
 monitor.c             |   1 +
 qemu-options.hx       |  17 +++++--
 qtest.c               |  13 ++++-
 vl.c                  |  39 ++++++++++++---
 7 files changed, 241 insertions(+), 18 deletions(-)

-- 
2.0.0.rc2