Re: [PATCH v4 11/24] net: Use virtual time for net announce

[Nicholas Piggin]

On Tue Mar 12, 2024 at 9:12 PM AEST, Pavel Dovgalyuk wrote:
> On 12.03.2024 14:05, Nicholas Piggin wrote:
> > On Tue Mar 12, 2024 at 7:09 PM AEST, Pavel Dovgalyuk wrote:
> >> This won't work, as needed. Announce timer can't be enabled, because
> >> it is set in post_load function. Therefore announce callbacks break
> >> the replay, when virtio-net is used with snapshots.
> > 
> > I see. Is that somehow marked as being incompatible with rr?
>
> Here's the prior discussion on it: 
> https://lore.kernel.org/qemu-devel/8735ovx0zd.fsf@linaro.org/t/

Thanks for that context. You already fixed some of these, lol that
would have saved me a few hours. Maybe clearing the announce flag
is the right way to solve this, I might take that instead.

Trouble is we have virtio-net selftests in tests already and this
causes failures. So we need to get it fixed. I do think the bh API
is a bit clunky and could be revised into a name that makes more
sense for the non-replay developer, but that's really a separate
issue and should not prevent this bug fixes being merged.

We really need non-flaky rr testing upstream because it's quite
easy to break. So I will keep trying to get these merged.

Thanks,
Nick

>
>
> > 
> > Thanks,
> > Nick
> > 
> >>
> >> On 11.03.2024 20:40, Nicholas Piggin wrote:
> >>> Using virtual time for announce ensures that guest visible effects
> >>> are deterministic and don't break replay.
> >>>
> >>> Signed-off-by: Nicholas Piggin <npiggin@gmail.com>
> >>> ---
> >>>    net/announce.c | 2 +-
> >>>    1 file changed, 1 insertion(+), 1 deletion(-)
> >>>
> >>> diff --git a/net/announce.c b/net/announce.c
> >>> index 9e99044422..70b5d5e822 100644
> >>> --- a/net/announce.c
> >>> +++ b/net/announce.c
> >>> @@ -187,7 +187,7 @@ static void qemu_announce_self_once(void *opaque)
> >>>    
> >>>    void qemu_announce_self(AnnounceTimer *timer, AnnounceParameters 
> >>> *params)
> >>>    {
> >>> -    qemu_announce_timer_reset(timer, params, QEMU_CLOCK_REALTIME,
> >>> +    qemu_announce_timer_reset(timer, params, QEMU_CLOCK_VIRTUAL,
> >>>                                  qemu_announce_self_once, timer);
> >>>        if (params->rounds) {
> >>>            qemu_announce_self_once(timer);
> >