netdev - Re: [PATCH net-next v2] virtio_net: add support for Byte Queue Limits

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Date: Mon, 17 Jun 2024 11:18:19 +0200
From: Jiri Pirko <jiri@...nulli.us>
To: Jason Wang <jasowang@...hat.com>
Cc: netdev@...r.kernel.org, davem@...emloft.net, edumazet@...gle.com,
	kuba@...nel.org, pabeni@...hat.com, mst@...hat.com,
	xuanzhuo@...ux.alibaba.com, virtualization@...ts.linux.dev,
	ast@...nel.org, daniel@...earbox.net, hawk@...nel.org,
	john.fastabend@...il.com, dave.taht@...il.com,
	kerneljasonxing@...il.com, hengqi@...ux.alibaba.com
Subject: Re: [PATCH net-next v2] virtio_net: add support for Byte Queue Limits

Mon, Jun 17, 2024 at 04:34:26AM CEST, jasowang@...hat.com wrote:
>On Thu, Jun 13, 2024 at 1:09 AM Jiri Pirko <jiri@...nulli.us> wrote:
>>
>> From: Jiri Pirko <jiri@...dia.com>
>>
>> Add support for Byte Queue Limits (BQL).
>>
>> Tested on qemu emulated virtio_net device with 1, 2 and 4 queues.
>> Tested with fq_codel and pfifo_fast. Super netperf with 50 threads is
>> running in background. Netperf TCP_RR results:
>>
>> NOBQL FQC 1q:  159.56  159.33  158.50  154.31    agv: 157.925
>> NOBQL FQC 2q:  184.64  184.96  174.73  174.15    agv: 179.62
>> NOBQL FQC 4q:  994.46  441.96  416.50  499.56    agv: 588.12
>> NOBQL PFF 1q:  148.68  148.92  145.95  149.48    agv: 148.2575
>> NOBQL PFF 2q:  171.86  171.20  170.42  169.42    agv: 170.725
>> NOBQL PFF 4q: 1505.23 1137.23 2488.70 3507.99    agv: 2159.7875
>>   BQL FQC 1q: 1332.80 1297.97 1351.41 1147.57    agv: 1282.4375
>>   BQL FQC 2q:  768.30  817.72  864.43  974.40    agv: 856.2125
>>   BQL FQC 4q:  945.66  942.68  878.51  822.82    agv: 897.4175
>>   BQL PFF 1q:  149.69  151.49  149.40  147.47    agv: 149.5125
>>   BQL PFF 2q: 2059.32  798.74 1844.12  381.80    agv: 1270.995
>>   BQL PFF 4q: 1871.98 4420.02 4916.59 13268.16   agv: 6119.1875
>>
>> Signed-off-by: Jiri Pirko <jiri@...dia.com>
>> ---
>> v1->v2:
>> - moved netdev_tx_completed_queue() call into __free_old_xmit(),
>>   propagate use_napi flag to __free_old_xmit() and only call
>>   netdev_tx_completed_queue() in case it is true
>> - added forgotten call to netdev_tx_reset_queue()
>> - fixed stats for xdp packets
>> - fixed bql accounting when __free_old_xmit() is called from xdp path
>> - handle the !use_napi case in start_xmit() kick section
>> ---
>>  drivers/net/virtio_net.c | 50 +++++++++++++++++++++++++---------------
>>  1 file changed, 32 insertions(+), 18 deletions(-)
>>
>> diff --git a/drivers/net/virtio_net.c b/drivers/net/virtio_net.c
>> index 61a57d134544..5863c663ccab 100644
>> --- a/drivers/net/virtio_net.c
>> +++ b/drivers/net/virtio_net.c
>> @@ -84,7 +84,9 @@ struct virtnet_stat_desc {
>>
>>  struct virtnet_sq_free_stats {
>>         u64 packets;
>> +       u64 xdp_packets;
>>         u64 bytes;
>> +       u64 xdp_bytes;
>>  };
>>
>>  struct virtnet_sq_stats {
>> @@ -506,29 +508,33 @@ static struct xdp_frame *ptr_to_xdp(void *ptr)
>>         return (struct xdp_frame *)((unsigned long)ptr & ~VIRTIO_XDP_FLAG);
>>  }
>>
>> -static void __free_old_xmit(struct send_queue *sq, bool in_napi,
>> +static void __free_old_xmit(struct send_queue *sq, struct netdev_queue *txq,
>> +                           bool in_napi, bool use_napi,
>>                             struct virtnet_sq_free_stats *stats)
>>  {
>>         unsigned int len;
>>         void *ptr;
>>
>>         while ((ptr = virtqueue_get_buf(sq->vq, &len)) != NULL) {
>> -               ++stats->packets;
>> -
>>                 if (!is_xdp_frame(ptr)) {
>>                         struct sk_buff *skb = ptr;
>>
>>                         pr_debug("Sent skb %p\n", skb);
>>
>> +                       stats->packets++;
>>                         stats->bytes += skb->len;
>>                         napi_consume_skb(skb, in_napi);
>>                 } else {
>>                         struct xdp_frame *frame = ptr_to_xdp(ptr);
>>
>> -                       stats->bytes += xdp_get_frame_len(frame);
>> +                       stats->xdp_packets++;
>> +                       stats->xdp_bytes += xdp_get_frame_len(frame);
>>                         xdp_return_frame(frame);
>>                 }
>>         }
>> +       if (use_napi)
>> +               netdev_tx_completed_queue(txq, stats->packets, stats->bytes);
>> +
>>  }
>
>I wonder if this works correctly, for example NAPI could be enabled
>after queued but before sent. So __netdev_tx_sent_queue() is not
>called before.

How is that possible? Napi weight can't change when link is up. Or am I
missing something?

>
>Thanks
>