Paolo Bonzini <pbonz...@redhat.com> writes: > On 05/04/2017 15:25, Alex Bennée wrote: >> This ensures each time the vCPU thread reads the icount we update the >> master timer_state.qemu_icount field. This way as long as updates are >> in BQL protected sections (which they should be) the main-loop can >> never come to update the log and find time has gone backwards. >> >> Signed-off-by: Alex Bennée <alex.ben...@linaro.org> >> --- >> cpus.c | 6 ++---- >> 1 file changed, 2 insertions(+), 4 deletions(-) >> >> diff --git a/cpus.c b/cpus.c >> index ff75af449a..63de033cc8 100644 >> --- a/cpus.c >> +++ b/cpus.c >> @@ -246,19 +246,17 @@ void cpu_update_icount(CPUState *cpu) >> >> int64_t cpu_get_icount_raw(void) >> { >> - int64_t icount; >> CPUState *cpu = current_cpu; >> >> - icount = atomic_read(&timers_state.qemu_icount); >> if (cpu && cpu->running) { >> if (!cpu->can_do_io) { >> fprintf(stderr, "Bad icount read\n"); >> exit(1); >> } >> /* Take into account what has run */ >> - icount += cpu_get_icount_executed(cpu); >> + cpu_update_icount(cpu); >> } >> - return icount; >> + return atomic_read(&timers_state.qemu_icount); >> } >> >> /* Return the virtual CPU time, based on the instruction counter. */ >> > > Maybe the update should be done in gen_io_start instead. There > shouldn't be any interference between vCPU and I/O threads except > between gen_io_start and gen_io_end.
I'm not sure I follow. gen_io_start is a translation time thing. At least here we ensure we update whenever the value is read. -- Alex Bennée