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:
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
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
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