Re: [PATCH net-next v5 15/15] virtio-net: xsk zero copy xmit kick by threshold

[Jason Wang <jasowang@redhat.com>]

在 2021/6/17 下午1:56, Xuan Zhuo 写道:
> On Thu, 17 Jun 2021 11:08:34 +0800, Jason Wang <jasowang@redhat.com> wrote:
>> 在 2021/6/10 下午4:22, Xuan Zhuo 写道:
>>> After testing, the performance of calling kick every time is not stable.
>>> And if all the packets are sent and kicked again, the performance is not
>>> good. So add a module parameter to specify how many packets are sent to
>>> call a kick.
>>>
>>> 8 is a relatively stable value with the best performance.
>>>
>>> Here is the pps of the test of xsk_kick_thr under different values (from
>>> 1 to 64).
>>>
>>> thr  PPS             thr PPS             thr PPS
>>> 1    2924116.74247 | 23  3683263.04348 | 45  2777907.22963
>>> 2    3441010.57191 | 24  3078880.13043 | 46  2781376.21739
>>> 3    3636728.72378 | 25  2859219.57656 | 47  2777271.91304
>>> 4    3637518.61468 | 26  2851557.9593  | 48  2800320.56575
>>> 5    3651738.16251 | 27  2834783.54408 | 49  2813039.87599
>>> 6    3652176.69231 | 28  2847012.41472 | 50  3445143.01839
>>> 7    3665415.80602 | 29  2860633.91304 | 51  3666918.01281
>>> 8    3665045.16555 | 30  2857903.5786  | 52  3059929.2709
>>
>> I wonder what's the number for the case of non zc xsk?
>
> These data are used to compare the situation of sending different numbers of
> packets to virtio at one time. I think it has nothing to do with non-zerocopy
> xsk.


Yes, but it would be helpful to see how much we can gain from zerocopy.

Thanks


>
> Thanks.
>
>> Thanks
>>
>>
>>> 9    3671023.2401  | 31  2835589.98963 | 53  2831515.21739
>>> 10   3669532.23274 | 32  2862827.88706 | 54  3451804.07204
>>> 11   3666160.37749 | 33  2871855.96696 | 55  3654975.92385
>>> 12   3674951.44813 | 34  3434456.44816 | 56  3676198.3188
>>> 13   3667447.57331 | 35  3656918.54177 | 57  3684740.85619
>>> 14   3018846.0503  | 36  3596921.16722 | 58  3060958.8594
>>> 15   2792773.84505 | 37  3603460.63903 | 59  2828874.57191
>>> 16   3430596.3602  | 38  3595410.87666 | 60  3459926.11027
>>> 17   3660525.85806 | 39  3604250.17819 | 61  3685444.47599
>>> 18   3045627.69054 | 40  3596542.28428 | 62  3049959.0809
>>> 19   2841542.94177 | 41  3600705.16054 | 63  2806280.04013
>>> 20   2830475.97348 | 42  3019833.71191 | 64  3448494.3913
>>> 21   2845655.55789 | 43  2752951.93264 |
>>> 22   3450389.84365 | 44  2753107.27164 |
>>>
>>> It can be found that when the value of xsk_kick_thr is relatively small,
>>> the performance is not good, and when its value is greater than 13, the
>>> performance will be more irregular and unstable. It looks similar from 3
>>> to 13, I chose 8 as the default value.
>>>
>>> The test environment is qemu + vhost-net. I modified vhost-net to drop
>>> the packets sent by vm directly, so that the cpu of vm can run higher.
>>> By default, the processes in the vm and the cpu of softirqd are too low,
>>> and there is no obvious difference in the test data.
>>>
>>> During the test, the cpu of softirq reached 100%. Each xsk_kick_thr was
>>> run for 300s, the pps of every second was recorded, and the average of
>>> the pps was finally taken. The vhost process cpu on the host has also
>>> reached 100%.
>>>
>>> Signed-off-by: Xuan Zhuo <xuanzhuo@linux.alibaba.com>
>>> Reviewed-by: Dust Li <dust.li@linux.alibaba.com>
>>> ---
>>>    drivers/net/virtio/virtio_net.c |  1 +
>>>    drivers/net/virtio/xsk.c        | 18 ++++++++++++++++--
>>>    drivers/net/virtio/xsk.h        |  2 ++
>>>    3 files changed, 19 insertions(+), 2 deletions(-)
>>>
>>> diff --git a/drivers/net/virtio/virtio_net.c b/drivers/net/virtio/virtio_net.c
>>> index 9503133e71f0..dfe509939b45 100644
>>> --- a/drivers/net/virtio/virtio_net.c
>>> +++ b/drivers/net/virtio/virtio_net.c
>>> @@ -14,6 +14,7 @@ static bool csum = true, gso = true, napi_tx = true;
>>>    module_param(csum, bool, 0444);
>>>    module_param(gso, bool, 0444);
>>>    module_param(napi_tx, bool, 0644);
>>> +module_param(xsk_kick_thr, int, 0644);
>>>
>>>    /* FIXME: MTU in config. */
>>>    #define GOOD_PACKET_LEN (ETH_HLEN + VLAN_HLEN + ETH_DATA_LEN)
>>> diff --git a/drivers/net/virtio/xsk.c b/drivers/net/virtio/xsk.c
>>> index 3973c82d1ad2..2f3ba6ab4798 100644
>>> --- a/drivers/net/virtio/xsk.c
>>> +++ b/drivers/net/virtio/xsk.c
>>> @@ -5,6 +5,8 @@
>>>
>>>    #include "virtio_net.h"
>>>
>>> +int xsk_kick_thr = 8;
>>> +
>>>    static struct virtio_net_hdr_mrg_rxbuf xsk_hdr;
>>>
>>>    static struct virtnet_xsk_ctx *virtnet_xsk_ctx_get(struct virtnet_xsk_ctx_head *head)
>>> @@ -455,6 +457,7 @@ static int virtnet_xsk_xmit_batch(struct send_queue *sq,
>>>    	struct xdp_desc desc;
>>>    	int err, packet = 0;
>>>    	int ret = -EAGAIN;
>>> +	int need_kick = 0;
>>>
>>>    	while (budget-- > 0) {
>>>    		if (sq->vq->num_free < 2 + MAX_SKB_FRAGS) {
>>> @@ -475,11 +478,22 @@ static int virtnet_xsk_xmit_batch(struct send_queue *sq,
>>>    		}
>>>
>>>    		++packet;
>>> +		++need_kick;
>>> +		if (need_kick > xsk_kick_thr) {
>>> +			if (virtqueue_kick_prepare(sq->vq) &&
>>> +			    virtqueue_notify(sq->vq))
>>> +				++stats->kicks;
>>> +
>>> +			need_kick = 0;
>>> +		}
>>>    	}
>>>
>>>    	if (packet) {
>>> -		if (virtqueue_kick_prepare(sq->vq) && virtqueue_notify(sq->vq))
>>> -			++stats->kicks;
>>> +		if (need_kick) {
>>> +			if (virtqueue_kick_prepare(sq->vq) &&
>>> +			    virtqueue_notify(sq->vq))
>>> +				++stats->kicks;
>>> +		}
>>>
>>>    		*done += packet;
>>>    		stats->xdp_tx += packet;
>>> diff --git a/drivers/net/virtio/xsk.h b/drivers/net/virtio/xsk.h
>>> index fe22cf78d505..4f0f4f9cf23b 100644
>>> --- a/drivers/net/virtio/xsk.h
>>> +++ b/drivers/net/virtio/xsk.h
>>> @@ -7,6 +7,8 @@
>>>
>>>    #define VIRTNET_XSK_BUFF_CTX  ((void *)(unsigned long)~0L)
>>>
>>> +extern int xsk_kick_thr;
>>> +
>>>    /* When xsk disable, under normal circumstances, the network card must reclaim
>>>     * all the memory that has been sent and the memory added to the rq queue by
>>>     * destroying the queue.