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)
avg packets drop before: 2842
avg packets drop after: 360(-87.3%)
Just let me know if it looks good enough. Thx.
Jiang
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