Re: [PATCH v2 12/17] migration/multifd: Device state transfer support - send side

[Peter Xu]

On Tue, Aug 27, 2024 at 07:54:31PM +0200, Maciej S. Szmigiero wrote:
> +bool multifd_queue_device_state(char *idstr, uint32_t instance_id,
> +                                char *data, size_t len)
> +{
> +    /* Device state submissions can come from multiple threads */
> +    QEMU_LOCK_GUARD(&queue_job_mutex);

Ah, just notice there's the mutex.

So please consider the reply in the other thread, IIUC we can make it for
multifd_send() to be a generic mutex to simplify the other patch too, then
drop here.

I assume the ram code should be fine taking one more mutex even without
vfio, if it only takes once for each ~128 pages to enqueue, and only take
in the main thread, then each update should be also in the hot path
(e.g. no cache bouncing).

> +    MultiFDDeviceState_t *device_state;
> +
> +    assert(multifd_payload_empty(device_state_send));
> +
> +    multifd_set_payload_type(device_state_send, 
> MULTIFD_PAYLOAD_DEVICE_STATE);
> +    device_state = &device_state_send->u.device_state;
> +    device_state->idstr = g_strdup(idstr);
> +    device_state->instance_id = instance_id;
> +    device_state->buf = g_memdup2(data, len);
> +    device_state->buf_len = len;
> +
> +    if (!multifd_send(&device_state_send)) {
> +        multifd_send_data_clear(device_state_send);
> +        return false;
> +    }
> +
> +    return true;
> +}

-- 
Peter Xu