Re: [Qemu-devel] [RFC Patch v2 05/10] virtio-net rsc: Create timer to drain the packets from the cache pool

[Jason Wang]

On 02/01/2016 04:39 PM, Wei Xu wrote:
> On 02/01/2016 02:28 PM, Jason Wang wrote:
>>
>> On 02/01/2016 02:13 AM, address@hidden wrote:
>>> From: Wei Xu <address@hidden>
>>>
>>> The timer will only be triggered if the packets pool is not empty,
>>> and it'll drain off all the cached packets, this is to reduce the
>>> delay to upper layer protocol stack.
>>>
>>> Signed-off-by: Wei Xu <address@hidden>
>>> ---
>>>   hw/net/virtio-net.c | 38 ++++++++++++++++++++++++++++++++++++++
>>>   1 file changed, 38 insertions(+)
>>>
>>> diff --git a/hw/net/virtio-net.c b/hw/net/virtio-net.c
>>> index 4f77fbe..93df0d5 100644
>>> --- a/hw/net/virtio-net.c
>>> +++ b/hw/net/virtio-net.c
>>> @@ -48,12 +48,17 @@
>>>     #define MAX_VIRTIO_IP_PAYLOAD  (65535 + IP_OFFSET)
>>>   +/* Purge coalesced packets timer interval */
>>> +#define RSC_TIMER_INTERVAL  500000
>> Any hints for choosing this as default value? Do we need a property for
>> user to change this?
> This is still under estimation, 300ms -500ms is a good value to adapt
> the test, this should be configurable.
>>> +
>>>   /* Global statistics */
>>>   static uint32_t rsc_chain_no_mem;
>>>     /* Switcher to enable/disable rsc */
>>>   static bool virtio_net_rsc_bypass;
>>>   +static uint32_t rsc_timeout = RSC_TIMER_INTERVAL;
>>> +
>>>   /* Coalesce callback for ipv4/6 */
>>>   typedef int32_t (VirtioNetCoalesce) (NetRscChain *chain, NetRscSeg
>>> *seg,
>>>                                        const uint8_t *buf, size_t
>>> size);
>>> @@ -1625,6 +1630,35 @@ static int
>>> virtio_net_load_device(VirtIODevice *vdev, QEMUFile *f,
>>>       return 0;
>>>   }
>>>   +static void virtio_net_rsc_purge(void *opq)
>>> +{
>>> +    int ret = 0;
>>> +    NetRscChain *chain = (NetRscChain *)opq;
>>> +    NetRscSeg *seg, *rn;
>>> +
>>> +    QTAILQ_FOREACH_SAFE(seg, &chain->buffers, next, rn) {
>>> +        if (!qemu_can_send_packet(seg->nc)) {
>>> +            /* Should quit or continue? not sure if one or some
>>> +            * of the queues fail would happen, try continue here */
>> This looks wrong, qemu_can_send_packet() is used for nc's peer not nc
>> itself.
> OK.
>>
>>> +            continue;
>>> +        }
>>> +
>>> +        ret = virtio_net_do_receive(seg->nc, seg->buf, seg->size);
>>> +        QTAILQ_REMOVE(&chain->buffers, seg, next);
>>> +        g_free(seg->buf);
>>> +        g_free(seg);
>>> +
>>> +        if (ret == 0) {
>>> +            /* Try next queue */
>> Try next seg?
> Yes, it's seg.
>>
>>> +            continue;
>>> +        }
>> Why need above?
> yes, it's optional, my maybe can help if there are extra codes after
> this, will remove this.
>>
>>> +    }
>>> +
>>> +    if (!QTAILQ_EMPTY(&chain->buffers)) {
>>> +        timer_mod(chain->drain_timer,
>>> +                  qemu_clock_get_ns(QEMU_CLOCK_VIRTUAL) +
>>> rsc_timeout);
>> Need stop/start the timer during vm stop/start to save cpu.
> Thanks, do you know where should i add the code?

You may want to look at the vmstate change handler in virtio-net.c.