----- Original Message -----
> From: "Peter Maydell" <peter.mayd...@linaro.org>
> To: "Paolo Bonzini" <pbonz...@redhat.com>
> Cc: "QEMU Developers" <qemu-devel@nongnu.org>, "Alex Bennée"
> <alex.ben...@linaro.org>, "Richard Henderson"
> <r...@twiddle.net>, "Emilio G. Cota" <c...@braap.org>, "Pavel Dovgalyuk"
> <dovga...@ispras.ru>
> Sent: Thursday, April 5, 2018 7:35:56 PM
> Subject: Re: TCG icount interaction with timer deadlines
>
> On 5 April 2018 at 18:07, Paolo Bonzini <pbonz...@redhat.com> wrote:
> > On 05/04/2018 18:01, Peter Maydell wrote:
> >> * however, if the guest reprograms the clock during the tcg_cpu_exec()
> >> run, we don't do anything to cause us to stop earlier
> >
> > Anything that does this from the vCPU thread should be between
> > gen_icount_start and gen_icount_end. (In fact, it's the entire reason
> > why cpu_io_recompile exists).
>
> Yes, and this does cause us to do a cpu_io_recompile, which
> rebuilds the TB and does a longjmp. However:
> (1) that only takes us out to cpu_exec(), which will then
> just go ahead and execute the next TB, whereas the
> recalculation of deadlines happens at the next level out
> in tcg_cpu_exec()
> (2) the io_recompile happens *before* the guest writes to
> the timer register that reprograms the deadline, so even
> if we recomputed deadlines after this longjmp they wouldn't
> be correct
Right - that part would be handled here:
void qemu_timer_notify_cb(void *opaque, QEMUClockType type)
{
if (!use_icount || type != QEMU_CLOCK_VIRTUAL) {
qemu_notify_event();
return;
}
if (!qemu_in_vcpu_thread() && first_cpu) {
/* qemu_cpu_kick is not enough to kick a halted CPU out of
* qemu_tcg_wait_io_event. async_run_on_cpu, instead,
* causes cpu_thread_is_idle to return false. This way,
* handle_icount_deadline can run.
*/
async_run_on_cpu(first_cpu, do_nothing, RUN_ON_CPU_NULL);
}
}
(called by timerlist_notify, called in turn by timerlist_rearm)
but that second "if" is too restrictive. Maybe just removing
the first arm is enough. All this was broken by MTTCG.
Paolo
