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 the 'align' parameter for icount and changes the icount option from '-icount [N|auto]' to '-icount [icount=][N|auto][,align]'. The second 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 third 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 the icount_time_shift. The forth and final 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 printif the align option is enabled. Sebastian Tanase (4): icount: Add 'align' and 'icount' options icount: Make icount_time_shift available everywhere cpu_exec: Add sleeping algorithm cpu_exec: Print to console if the guest is late cpu-exec.c | 104 ++++++++++++++++++++++++++++++++++++++++++++++++++ cpus.c | 10 ++++- include/qemu-common.h | 2 + qemu-options.hx | 19 +++++++-- vl.c | 26 ++++++++++++- 5 files changed, 155 insertions(+), 6 deletions(-) -- 2.0.0.rc2
