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Re: [Qemu-devel] [RFC Patch v2 04/10] virtio-net rsc: Detailed IPv4 and
From: |
Jason Wang |
Subject: |
Re: [Qemu-devel] [RFC Patch v2 04/10] virtio-net rsc: Detailed IPv4 and General TCP data coalescing |
Date: |
Mon, 1 Feb 2016 17:29:35 +0800 |
User-agent: |
Mozilla/5.0 (X11; Linux x86_64; rv:38.0) Gecko/20100101 Thunderbird/38.5.1 |
On 02/01/2016 04:29 PM, Wei Xu wrote:
>
> On 02/01/2016 02:21 PM, Jason Wang wrote:
>
>>
>> On 02/01/2016 02:13 AM, address@hidden wrote:
>>> From: Wei Xu <address@hidden>
>>>
>>> Since this feature also needs to support IPv6, and there are
>>> some protocol specific differences difference for IPv4/6 in the header,
>>> so try to make the interface to be general.
>>>
>>> IPv4/6 should set up both the new and old IP/TCP header before invoking
>>> TCP coalescing, and should also tell the real payload.
>>>
>>> The main handler of TCP includes TCP window update, duplicated ACK
>>> check
>>> and the real data coalescing if the new segment passed invalid filter
>>> and is identified as an expected one.
>>>
>>> An expected segment means:
>>> 1. Segment is within current window and the sequence is the expected
>>> one.
>>> 2. ACK of the segment is in the valid window.
>>> 3. If the ACK in the segment is a duplicated one, then it must less
>>> than 2,
>>> this is to notify upper layer TCP starting retransmission due to
>>> the spec.
>>>
>>> Signed-off-by: Wei Xu <address@hidden>
>>> ---
>>> hw/net/virtio-net.c | 127
>>> ++++++++++++++++++++++++++++++++++++++++++++++++++--
>>> 1 file changed, 124 insertions(+), 3 deletions(-)
>>>
>>> diff --git a/hw/net/virtio-net.c b/hw/net/virtio-net.c
>>> index cfbac6d..4f77fbe 100644
>>> --- a/hw/net/virtio-net.c
>>> +++ b/hw/net/virtio-net.c
>>> @@ -41,6 +41,10 @@
>>> #define VIRTIO_HEADER 12 /* Virtio net header size */
>>> #define IP_OFFSET (VIRTIO_HEADER + sizeof(struct eth_header))
>>> +#define TCP_WINDOW 65535
>> The name is confusing, how about TCP_MAX_WINDOW_SIZE ?
>
> Sounds better, will take it in.
>
>>
>>> +
>>> +/* IPv4 max payload, 16 bits in the header */
>>> +#define MAX_IP4_PAYLOAD (65535 - sizeof(struct ip_header))
>>> #define MAX_VIRTIO_IP_PAYLOAD (65535 + IP_OFFSET)
>>> @@ -1670,13 +1674,130 @@ out:
>>> return 0;
>>> }
>>> +static int32_t virtio_net_rsc_handle_ack(NetRscChain *chain,
>>> NetRscSeg *seg,
>>> + const uint8_t *buf, struct
>>> tcp_header *n_tcp,
>>> + struct tcp_header *o_tcp)
>>> +{
>>> + uint32_t nack, oack;
>>> + uint16_t nwin, owin;
>>> +
>>> + nack = htonl(n_tcp->th_ack);
>>> + nwin = htons(n_tcp->th_win);
>>> + oack = htonl(o_tcp->th_ack);
>>> + owin = htons(o_tcp->th_win);
>>> +
>>> + if ((nack - oack) >= TCP_WINDOW) {
>>> + return RSC_FINAL;
>>> + } else if (nack == oack) {
>>> + /* duplicated ack or window probe */
>>> + if (nwin == owin) {
>>> + /* duplicated ack, add dup ack count due to whql test
>>> up to 1 */
>>> +
>>> + if (seg->dup_ack_count == 0) {
>>> + seg->dup_ack_count++;
>>> + return RSC_COALESCE;
>>> + } else {
>>> + /* Spec says should send it directly */
>>> + return RSC_FINAL;
>>> + }
>>> + } else {
>>> + /* Coalesce window update */
>> Need we flush this immediately consider it was a window update?
>
> The flowchart in the spec says this can be coalesced as normal.
>
> https://msdn.microsoft.com/en-us/library/windows/hardware/jj853325%28v=vs.85%29.aspx
I see.
>
>
>>
>>> + o_tcp->th_win = n_tcp->th_win;
>>> + return RSC_COALESCE;
>>> + }
>>> + } else {
>> What if nack < oack here?
>
> That should happen, the modulo-232 arithmetic check at the begin of
> this function will keep the ack is in the current window.
Ok.
Thanks