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=on|off]'. 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. All the parts in cpu-exec.c are only compiled for soft-mmu architectures otherwise the code will not compile for all architectures (linux-user and soft-mmu). The forth patch updates the algorithm to take into account an initial offset between clocks. The offset can be 0 (for example on ARM) or another value (typically it is almost equal to the realtime clock) on other architectures (for example on x86). The fifth 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 print if the align option is enabled. v1 -> v2 * Signal errors in configure_icount() as suggested by Paolo Bonzini (patch 1). * Update qtest.c to take into account the new configure_icount() (patch 1). * Surround delay code in cpu-exec.c with !defined(CONFIG_USER_ONLY) (patch 3). * Clean up delay code in cpu-exec.c as suggested by Paolo Bonzini and Juan Quintela (patch 3). * Take into account initial offset between real and virtual clocks (patch 4). Sebastian Tanase (5): icount: Add 'align' and 'icount' options icount: Make icount_time_shift available everywhere cpu_exec: Add sleeping algorithm icount_warp: Take into account initial offset between clocks cpu_exec: Print to console if the guest is late cpu-exec.c | 108 +++++++++++++++++++++++++++++++++++++++++++++- cpus.c | 38 ++++++++++++++-- include/qapi/qmp/qerror.h | 9 ++++ include/qemu-common.h | 6 ++- qemu-options.hx | 19 ++++++-- qtest.c | 19 +++++++- vl.c | 43 +++++++++++++++--- 7 files changed, 225 insertions(+), 17 deletions(-) -- 2.0.0.rc2
