On 2019/8/15 17:25, Jason Wang wrote:
>
> On 2019/8/15 下午4:36, 冉 jiang wrote:
>> On 2019/8/15 11:17, Jason Wang wrote:
>>> On 2019/8/15 上午11:11, 冉 jiang wrote:
>>>> On 2019/8/15 11:01, Jason Wang wrote:
>>>>> On 2019/8/14 上午10:06, ? jiang wrote:
>>>>>> This change lowers ring buffer reclaim threshold from 1/2*queue to
>>>>>> budget
>>>>>> for better performance. According to our test with qemu + dpdk,
>>>>>> packet
>>>>>> dropping happens when the guest is not able to provide free
>>>>>> buffer in
>>>>>> avail ring timely with default 1/2*queue. The value in the patch has
>>>>>> been
>>>>>> tested and does show better performance.
>>>>> Please add your tests setup and result here.
>>>>>
>>>>> Thanks
>>>>>
>>>>>
>>>>>> Signed-off-by: jiangkidd <jiangkidd@xxxxxxxxxxx>
>>>>>> ---
>>>>>> drivers/net/virtio_net.c | 2 +-
>>>>>> 1 file changed, 1 insertion(+), 1 deletion(-)
>>>>>>
>>>>>> diff --git a/drivers/net/virtio_net.c b/drivers/net/virtio_net.c
>>>>>> index 0d4115c9e20b..bc08be7925eb 100644
>>>>>> --- a/drivers/net/virtio_net.c
>>>>>> +++ b/drivers/net/virtio_net.c
>>>>>> @@ -1331,7 +1331,7 @@ static int virtnet_receive(struct
>>>>>> receive_queue
>>>>>> *rq, int budget,
>>>>>> }
>>>>>> }
>>>>>> - if (rq->vq->num_free > virtqueue_get_vring_size(rq->vq)
>>>>>> / 2) {
>>>>>> + if (rq->vq->num_free > min((unsigned int)budget,
>>>>>> virtqueue_get_vring_size(rq->vq)) / 2) {
>>>>>> if (!try_fill_recv(vi, rq, GFP_ATOMIC))
>>>>>> schedule_delayed_work(&vi->refill, 0);
>>>>>> }
>>>> Sure, here are the details:
>>>
>>> Thanks for the details, but I meant it's better if you could summarize
>>> you test result in the commit log in a compact way.
>>>
>>> Btw, some comments, see below:
>>>
>>>
>>>>
>>>> Test setup & result:
>>>>
>>>> ----------------------------------------------------
>>>>
>>>> Below is the snippet from our test result. Test1 was done with default
>>>> driver with the value of 1/2 * queue, while test2 is with my patch. We
>>>> can see average
>>>> drop packets do decrease a lot in test2.
>>>>
>>>> test1Time avgDropPackets test2Time avgDropPackets pps
>>>>
>>>> 16:21.0 12.295 56:50.4 0 300k
>>>> 17:19.1 15.244 56:50.4 0 300k
>>>> 18:17.5 18.789 56:50.4 0 300k
>>>> 19:15.1 14.208 56:50.4 0 300k
>>>> 20:13.2 20.818 56:50.4 0.267 300k
>>>> 21:11.2 12.397 56:50.4 0 300k
>>>> 22:09.3 12.599 56:50.4 0 300k
>>>> 23:07.3 15.531 57:48.4 0 300k
>>>> 24:05.5 13.664 58:46.5 0 300k
>>>> 25:03.7 13.158 59:44.5 4.73 300k
>>>> 26:01.1 2.486 00:42.6 0 300k
>>>> 26:59.1 11.241 01:40.6 0 300k
>>>> 27:57.2 20.521 02:38.6 0 300k
>>>> 28:55.2 30.094 03:36.7 0 300k
>>>> 29:53.3 16.828 04:34.7 0.963 300k
>>>> 30:51.3 46.916 05:32.8 0 400k
>>>> 31:49.3 56.214 05:32.8 0 400k
>>>> 32:47.3 58.69 05:32.8 0 400k
>>>> 33:45.3 61.486 05:32.8 0 400k
>>>> 34:43.3 72.175 05:32.8 0.598 400k
>>>> 35:41.3 56.699 05:32.8 0 400k
>>>> 36:39.3 61.071 05:32.8 0 400k
>>>> 37:37.3 43.355 06:30.8 0 400k
>>>> 38:35.4 44.644 06:30.8 0 400k
>>>> 39:33.4 72.336 06:30.8 0 400k
>>>> 40:31.4 70.676 06:30.8 0 400k
>>>> 41:29.4 108.009 06:30.8 0 400k
>>>> 42:27.4 65.216 06:30.8 0 400k
>>>
>>> Why there're difference in test time? Could you summarize them like:
>>>
>>> Test setup: e.g testpmd or pktgen to generate packets to guest
>>>
>>> avg packets drop before: XXX
>>>
>>> avg packets drop after: YYY(-ZZZ%)
>>>
>>> Thanks
>>>
>>>
>>>>
>>>> Data to prove why the patch helps:
>>>>
>>>> ----------------------------------------------------
>>>>
>>>> We did have completed several rounds of test with setting the value to
>>>> budget (64 as the default value). It does improve a lot with pps is
>>>> below 400pps for a single stream. We are confident that it runs out
>>>> of free
>>>> buffer in avail ring when packet dropping happens with below
>>>> systemtap:
>>>>
>>>> Just a snippet:
>>>>
>>>> probe module("virtio_ring").function("virtqueue_get_buf")
>>>> {
>>>> x = (@cast($_vq, "vring_virtqueue")->vring->used->idx)-
>>>> (@cast($_vq, "vring_virtqueue")->last_used_idx) ---> we use this one
>>>> to verify if the queue is full, which means guest is not able to take
>>>> buffer from the queue timely
>>>>
>>>> if (x<0 && (x+65535)<4096)
>>>> x = x+65535
>>>>
>>>> if((x==1024) && @cast($_vq,
>>>> "vring_virtqueue")->vq->callback ==
>>>> callback_addr)
>>>> netrxcount[x] <<< gettimeofday_s()
>>>> }
>>>>
>>>>
>>>> probe module("virtio_ring").function("virtqueue_add_inbuf")
>>>> {
>>>> y = (@cast($vq, "vring_virtqueue")->vring->avail->idx)-
>>>> (@cast($vq, "vring_virtqueue")->vring->used->idx) ---> we use this one
>>>> to verify if we run out of free buffer in avail ring
>>>> if (y<0 && (y+65535)<4096)
>>>> y = y+65535
>>>>
>>>> if(@2=="debugon")
>>>> {
>>>> if(y==0 && @cast($vq, "vring_virtqueue")->vq->callback ==
>>>> callback_addr)
>>>> {
>>>> netrxfreecount[y] <<< gettimeofday_s()
>>>>
>>>> printf("no avail ring left seen, printing most
>>>> recent 5
>>>> num free, vq: %lx, current index: %d\n", $vq, recentfreecount)
>>>> for(i=recentfreecount; i!=((recentfreecount+4) % 5);
>>>> i=((i+1) % 5))
>>>> {
>>>> printf("index: %d, num free: %d\n", i,
>>>> recentfree[$vq,
>>>> i])
>>>> }
>>>>
>>>> printf("index: %d, num free: %d\n", i, recentfree[$vq,
>>>> i])
>>>> //exit()
>>>> }
>>>> }
>>>> }
>>>>
>>>>
>>>> probe
>>>> module("virtio_net").statement("virtnet_receive@drivers/net/virtio_net.c:732")
>>>>
>>>>
>>>>
>>>> {
>>>> recentfreecount++
>>>> recentfreecount = recentfreecount % 5
>>>> recentfree[$rq->vq, recentfreecount] = $rq->vq->num_free --->
>>>> record the num_free for the last 5 calls to virtnet_receive, so we can
>>>> see if lowering the bar helps.
>>>> }
>>>>
>>>>
>>>> Here is the result:
>>>>
>>>> no avail ring left seen, printing most recent 5 num free, vq:
>>>> ffff9c13c1200000, current index: 1
>>>> index: 1, num free: 561
>>>> index: 2, num free: 305
>>>> index: 3, num free: 369
>>>> index: 4, num free: 433
>>>> index: 0, num free: 497
>>>> no avail ring left seen, printing most recent 5 num free, vq:
>>>> ffff9c13c1200000, current index: 1
>>>> index: 1, num free: 543
>>>> index: 2, num free: 463
>>>> index: 3, num free: 469
>>>> index: 4, num free: 476
>>>> index: 0, num free: 479
>>>> no avail ring left seen, printing most recent 5 num free, vq:
>>>> ffff9c13c1200000, current index: 2
>>>> index: 2, num free: 555
>>>> index: 3, num free: 414
>>>> index: 4, num free: 420
>>>> index: 0, num free: 427
>>>> index: 1, num free: 491
>>>>
>>>> We can see in the last 4 calls to virtnet_receive before we run out
>>>> of free buffer and start to relaim, num_free is quite high. So if we
>>>> can do the reclaim earlier, it will certainly help.
>>>>
>>>> Jiang
>>>
>>> Right, but I think there's no need to put those thing in the commit
>>> log.
>>>
>>> Thanks
>>>
>>>
>> Sure, here is the info:
>>
>>
>> Test setup: iperf3 to generate packets to guest (total 30mins, pps 400k)
>
>
> Please also note that type of packets e.g TCP or UDP.
>
> Thanks
>
>
>>
>> avg packets drop before: 2842
>>
>> avg packets drop after: 360(-87.3%)
>>
>>
>> Just let me know if it looks good enough. Thx.
>>
>> Jiang
>>
OK, just posted - "[PATCH v2] virtio-net: lower min ring num_free for
efficiency"
Jiang
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