Re: [Qemu-devel] What is the best commit for record-replay?

["Pavel Dovgalyuk" <dovgaluk@ispras.ru>]

> From: Alex Bennée [mailto:alex.bennee@linaro.org]
> >
> >>>
> >>>> >
> >>>> > Hope you've already found the solution (as the last post was on 2 May)
> >>>> > and it's just got missed the mailing list.
> >>>
> >>> As I know, RR is still broken in the current version.
> >>> It was caused by the MTTCG implementation.
> >>> Alex Bennee tried to fix RR back. Alex, have you found any solution?
> >>>
> >>> We also trying to find a way to fix RR. It seems, that we will reinvent BQL for RR.
> >>
> >> I think the method outlined in my RFC is the way to go, essentially the
> >> RR mutex taking over for the what the BQL did. The RFC patch hadn't
> >> hoisted the mutex for the additional devices so I'm just re-basing now
> >> and I'll see if I can make the changes for Igor's test case.
> >>
> >> --
> >> Alex Bennée
> 
> Could you try:
> 
>   https://github.com/stsquad/qemu/tree/bql-and-replay-locks-v2
> 
> And report back?

Most of the code look reasonable.
Isn't better to lock before acting with icount in the following function?
 
static void prepare_icount_for_run(CPUState *cpu)
{
    if (use_icount) {
        int insns_left;

        /* These should always be cleared by process_icount_data after
         * each vCPU execution. However u16.high can be raised
         * asynchronously by cpu_exit/cpu_interrupt/tcg_handle_interrupt
         */
        g_assert(cpu->icount_decr.u16.low == 0);
        g_assert(cpu->icount_extra == 0);

        cpu->icount_budget = tcg_get_icount_limit();
        insns_left = MIN(0xffff, cpu->icount_budget);
        cpu->icount_decr.u16.low = insns_left;
        cpu->icount_extra = cpu->icount_budget - insns_left;

        if (replay_mode != REPLAY_MODE_NONE) {
            replay_mutex_lock();
        }
    }
}



Pavel Dovgalyuk