Il 29/07/2013 17:27, Frederic Konrad ha scritto: > On 18/07/2013 17:35, Paolo Bonzini wrote: >> Il 18/07/2013 17:06, Peter Maydell ha scritto: >>> On 18 July 2013 16:02,<[email protected]> wrote: >>>> As I said in the last email, we have issues with determinism with >>>> icount. >>>> We are wondering if determinism is really ensured with icount? >>> My opinion is that it *should* be deterministic but it would >>> be unsurprising if the determinism had got broken along the way. >> First of all, it can only be deterministic if the guest satisfies (at >> least) all the following condition: >> >> 1) only uses timer that QEMU bases on vm_clock (which means that you >> should use "-rtc clock=vm"---sorry Fred, didn't think about this in the >> previous answer); >> >> 2) never does any network operation nor any asynchronous disk I/O >> operation >> >> 3) never halts the VCPU waiting for an interrupt > > Hi, > > qemu_alarm is making the replay not deterministic too.
What is qemu_alarm? If you mean qemu_alarm_timer, then that means rt_clock and host_clock (item 1 above)? If so, yes, I believe you need to record/replay them. When doing replay for reverse execution, you certainly want to execute at full speed without waiting for real time to pass again. Paolo > We tried to remove those alarms and it seems to replay well (at least > far better). > > So the question is: how we can solve that? > > We thought at two possibilities : > * record/replay them, like IO. > * base them on our new ic_clock. > > Both have drawbacks: > * record/replay won't make icount more deterministic (run to run). > * ic_clock speed time is apparently not constant. > > Thanks, > Fred >
