On Thu, May 31, 2012 at 9:48 PM, Jan Kiszka <jan.kis...@siemens.com> wrote:
> On 2012-05-31 15:45, Zhi Yong Wu wrote:
>> On Thu, May 31, 2012 at 5:18 PM, Stefan Hajnoczi <stefa...@gmail.com> wrote:
>>> On Wed, May 30, 2012 at 8:59 AM, Luigi Rizzo <ri...@iet.unipi.it> wrote:
>>>> Hi,
>>>> while investigating rx performance for emulated network devices
>>>> (i am looking at the userspace version, relying on net=tap
>>>> or similar approaches) i noticed the code
>>>> in net/queue.c :: qemu_net_queue_send()
>>>> which look strange to me (same goes for the iov version).
>>>>
>>>> The whole function is below, just for reference.
>>>> My impression is that the call to qemu_net_queue_flush()
>>>> is misplaced, and it should be before qemu_net_queue_deliver()
>>>> otherwise the current packet is pushed out before anything
>>>> was already in the queue.
>>>>
>>>> Does it make sense ?
>>>>
>>>> cheers
>>>> luigi
>>>>
>>>> ssize_t qemu_net_queue_send(NetQueue *queue,
>>>> VLANClientState *sender,
>>>> unsigned flags,
>>>> const uint8_t *data,
>>>> size_t size,
>>>> NetPacketSent *sent_cb)
>>>> {
>>>> ssize_t ret;
>>>>
>>>> if (queue->delivering) {
>>>> return qemu_net_queue_append(queue, sender, flags, data, size,
>>>> NULL);
>>>> }
>>>>
>>>> ret = qemu_net_queue_deliver(queue, sender, flags, data, size);
>>>> if (ret == 0) {
>>>> qemu_net_queue_append(queue, sender, flags, data, size,
>>>> sent_cb);
>>>> return 0;
>>>> }
>>>>
>>>> qemu_net_queue_flush(queue);
>>>
>>> This of the case where delivering a packet causes additional
>>> (re-entrant) qemu_net_queue_send() calls to this queue. We'll be in
>> If qemu_net_queue_send() are re-entranced, what issue or badness will
>> it introduce?
>> I haven't found what issue will take place when queue_flush() is moved
>> before queue_deliver().
>>
>
> Delayed packets that are hold back during delivering==1. Having a flush
Sorry, i don't get what it mean? You know, english is not my first
language.:) You mean that delayed packets may be reenqueued?
> before and after may be fine - if we really need it before.
>
> Jan
>
> --
> Siemens AG, Corporate Technology, CT T DE IT 1
> Corporate Competence Center Embedded Linux
--
Regards,
Zhi Yong Wu
