Re: [PATCH] replay: improve determinism of virtio-net

[Jason Wang]

在 2021/5/17 下午9:04, Pavel Dovgalyuk 写道:
> virtio-net device uses bottom halves for callbacks.
> These callbacks should be deterministic, because they affect VM state.
> This patch replaces BH invocations with corresponding replay functions,
> making them deterministic in record/replay mode.
> This patch also disables guest announce timers for record/replay,
> because they break correct loadvm in deterministic mode.


Virtio-net can be configured to work in tx timer mode. Do we need to 
care about that?


> Signed-off-by: Pavel Dovgalyuk <Pavel.Dovgalyuk@ispras.ru>
> ---
>   hw/net/virtio-net.c |   13 +++++++++----
>   1 file changed, 9 insertions(+), 4 deletions(-)
>
> diff --git a/hw/net/virtio-net.c b/hw/net/virtio-net.c
> index 6b7e8dd04e..e876363236 100644
> --- a/hw/net/virtio-net.c
> +++ b/hw/net/virtio-net.c
> @@ -44,6 +44,7 @@
>   #include "hw/pci/pci.h"
>   #include "net_rx_pkt.h"
>   #include "hw/virtio/vhost.h"
> +#include "sysemu/replay.h"
>   
>   #define VIRTIO_NET_VM_VERSION    11
>   
> @@ -394,7 +395,7 @@ static void virtio_net_set_status(struct VirtIODevice *vdev, uint8_t status)
>                   timer_mod(q->tx_timer,
>                                  qemu_clock_get_ns(QEMU_CLOCK_VIRTUAL) + 
> n->tx_timeout);
>               } else {
> -                qemu_bh_schedule(q->tx_bh);
> +                replay_bh_schedule_event(q->tx_bh);
>               }
>           } else {
>               if (q->tx_timer) {
> @@ -2546,7 +2547,7 @@ static void virtio_net_handle_tx_bh(VirtIODevice *vdev, 
> VirtQueue *vq)
>           return;
>       }
>       virtio_queue_set_notification(vq, 0);
> -    qemu_bh_schedule(q->tx_bh);
> +    replay_bh_schedule_event(q->tx_bh);


Not familiar with replay but any chance to change qemu_bh_schedule() 
instead?

Thanks


>   }
>   
>   static void virtio_net_tx_timer(void *opaque)
> @@ -2602,7 +2603,7 @@ static void virtio_net_tx_bh(void *opaque)
>       /* If we flush a full burst of packets, assume there are
>        * more coming and immediately reschedule */
>       if (ret >= n->tx_burst) {
> -        qemu_bh_schedule(q->tx_bh);
> +        replay_bh_schedule_event(q->tx_bh);
>           q->tx_waiting = 1;
>           return;
>       }
> @@ -2616,7 +2617,7 @@ static void virtio_net_tx_bh(void *opaque)
>           return;
>       } else if (ret > 0) {
>           virtio_queue_set_notification(q->tx_vq, 0);
> -        qemu_bh_schedule(q->tx_bh);
> +        replay_bh_schedule_event(q->tx_bh);
>           q->tx_waiting = 1;
>       }
>   }
> @@ -3206,6 +3207,10 @@ static void virtio_net_device_realize(DeviceState *dev, 
> Error **errp)
>           n->host_features |= (1ULL << VIRTIO_NET_F_MTU);
>       }
>   
> +    if (replay_mode != REPLAY_MODE_NONE) {
> +        n->host_features &= ~(1ULL << VIRTIO_NET_F_GUEST_ANNOUNCE);
> +    }
> +
>       if (n->net_conf.duplex_str) {
>           if (strncmp(n->net_conf.duplex_str, "half", 5) == 0) {
>               n->net_conf.duplex = DUPLEX_HALF;