Re: [RFC PATCH] replay: stop us hanging in rr_wait_io_event

[Peter Maydell]

On Tue, 5 Dec 2023 at 12:15, Alex Bennée <alex.bennee@linaro.org> wrote:
>
> A lot of the hang I see are when we end up spinning in
> rr_wait_io_event for an event that will never come in playback. As a
> new check functions which can see if we are in PLAY mode and kick us
> us the wait function so the event can be processed.
>
> This fixes most of the failures in replay_kernel.py
>
> Signed-off-by: Alex Bennée <alex.bennee@linaro.org>
> Cc: Pavel Dovgalyuk <pavel.dovgaluk@ispras.ru>
> ---
>  include/sysemu/replay.h      |  5 +++++
>  accel/tcg/tcg-accel-ops-rr.c |  2 +-
>  replay/replay.c              | 24 ++++++++++++++++++++++++
>  3 files changed, 30 insertions(+), 1 deletion(-)
>
> diff --git a/include/sysemu/replay.h b/include/sysemu/replay.h
> index 08aae5869f..83995ae4bd 100644
> --- a/include/sysemu/replay.h
> +++ b/include/sysemu/replay.h
> @@ -70,6 +70,11 @@ int replay_get_instructions(void);
>  /*! Updates instructions counter in replay mode. */
>  void replay_account_executed_instructions(void);
>
> +/**
> + * replay_can_wait: check if we should pause for wait-io
> + */
> +bool replay_can_wait(void);
> +
>  /* Processing clocks and other time sources */
>
>  /*! Save the specified clock */
> diff --git a/accel/tcg/tcg-accel-ops-rr.c b/accel/tcg/tcg-accel-ops-rr.c
> index 611932f3c3..825e35b3dc 100644
> --- a/accel/tcg/tcg-accel-ops-rr.c
> +++ b/accel/tcg/tcg-accel-ops-rr.c
> @@ -109,7 +109,7 @@ static void rr_wait_io_event(void)
>  {
>      CPUState *cpu;
>
> -    while (all_cpu_threads_idle()) {
> +    while (all_cpu_threads_idle() && replay_can_wait()) {
>          rr_stop_kick_timer();
>          qemu_cond_wait_iothread(first_cpu->halt_cond);
>      }
> diff --git a/replay/replay.c b/replay/replay.c
> index 0f7d766efe..e71cdbf819 100644
> --- a/replay/replay.c
> +++ b/replay/replay.c
> @@ -338,6 +338,30 @@ void replay_start(void)
>      replay_enable_events();
>  }
>
> +/*
> + * For none/record the answer is yes.
> + */
> +bool replay_can_wait(void)
> +{
> +    if (replay_mode == REPLAY_MODE_PLAY) {
> +        /*
> +         * For playback we shouldn't ever be at a point we wait. If

This comment sounds like "this can't happen, but it does for
some reason we don't understand" ... Is there some bug somewhere
that we're papering over here ?

thanks
-- PMM