[PATCH RFC 1/2] virtio-net: bql support

Jason Wang
Thu, 06 Dec 2018 08:31:24 -0000

On 2018/12/6 ??4:17, Jason Wang wrote:
>
> On 2018/12/6 ??6:54, Michael S. Tsirkin wrote:
>> When use_napi is set, let's enable BQLs. Note: some of the issues
are
>> similar to wifi.? It's worth considering whether something similar
to
>> commit 36148c2bbfbe ("mac80211: Adjust TSQ pacing shift")
might be
>> benefitial.
>
>
> I've played a similar patch several days before. The tricky part is
> the mode switching between napi and no napi. We should make sure when
> the packet is sent and trakced by BQL,? it should be consumed by BQL
> as well. I did it by tracking it through skb->cb.? And deal with the
> freeze by reset the BQL status. Patch attached.


Add the patch.

Thanks


>
> But when testing with vhost-net, I don't very a stable performance, it
> was probably because we batch the used ring updating so tx interrupt
> may come randomly. We probably need to implement time bounded
> coalescing mechanism which could be configured from userspace.
>
> Btw, maybe it's time just enable napi TX by default. I get ~10% TCP_RR
> regression on machine without APICv, (haven't found time to test APICv
> machine). But consider it was for correctness, I think it's
> acceptable? Then we can do optimization on top?
>
>
> Thanks
>
>
>> Signed-off-by: Michael S. Tsirkin <mst at redhat.com>
>> ---
>> ? drivers/net/virtio_net.c | 27 +++++++++++++++++++--------
>> ? 1 file changed, 19 insertions(+), 8 deletions(-)
>>
>> diff --git a/drivers/net/virtio_net.c b/drivers/net/virtio_net.c
>> index cecfd77c9f3c..b657bde6b94b 100644
>> --- a/drivers/net/virtio_net.c
>> +++ b/drivers/net/virtio_net.c
>> @@ -1325,7 +1325,8 @@ static int virtnet_receive(struct receive_queue
>> *rq, int budget,
>> ????? return stats.packets;
>> ? }
>> ? -static void free_old_xmit_skbs(struct send_queue *sq)
>> +static void free_old_xmit_skbs(struct send_queue *sq, struct
>> netdev_queue *txq,
>> +?????????????????? bool use_napi)
>> ? {
>> ????? struct sk_buff *skb;
>> ????? unsigned int len;
>> @@ -1347,6 +1348,9 @@ static void free_old_xmit_skbs(struct
>> send_queue *sq)
>> ????? if (!packets)
>> ????????? return;
>> ? +??? if (use_napi)
>> +??????? netdev_tx_completed_queue(txq, packets, bytes);
>> +
>> ????? u64_stats_update_begin(&sq->stats.syncp);
>> ????? sq->stats.bytes += bytes;
>> ????? sq->stats.packets += packets;
>> @@ -1364,7 +1368,7 @@ static void virtnet_poll_cleantx(struct
>> receive_queue *rq)
>> ????????? return;
>> ? ????? if (__netif_tx_trylock(txq)) {
>> -??????? free_old_xmit_skbs(sq);
>> +??????? free_old_xmit_skbs(sq, txq, true);
>> ????????? __netif_tx_unlock(txq);
>> ????? }
>> ? @@ -1440,7 +1444,7 @@ static int virtnet_poll_tx(struct napi_struct
>> *napi, int budget)
>> ????? struct netdev_queue *txq = netdev_get_tx_queue(vi->dev,
>> vq2txq(sq->vq));
>> ? ????? __netif_tx_lock(txq, raw_smp_processor_id());
>> -??? free_old_xmit_skbs(sq);
>> +??? free_old_xmit_skbs(sq, txq, true);
>> ????? __netif_tx_unlock(txq);
>> ? ????? virtqueue_napi_complete(napi, sq->vq, 0);
>> @@ -1505,13 +1509,15 @@ static netdev_tx_t start_xmit(struct sk_buff
>> *skb, struct net_device *dev)
>> ????? struct send_queue *sq = &vi->sq[qnum];
>> ????? int err;
>> ????? struct netdev_queue *txq = netdev_get_tx_queue(dev, qnum);
>> -??? bool kick = !skb->xmit_more;
>> +??? bool more = skb->xmit_more;
>> ????? bool use_napi = sq->napi.weight;
>> +??? unsigned int bytes = skb->len;
>> +??? bool kick;
>> ? ????? /* Free up any pending old buffers before queueing new ones. */
>> -??? free_old_xmit_skbs(sq);
>> +??? free_old_xmit_skbs(sq, txq, use_napi);
>> ? -??? if (use_napi && kick)
>> +??? if (use_napi && !more)
>> ????????? virtqueue_enable_cb_delayed(sq->vq);
>> ? ????? /* timestamp packet in software */
>> @@ -1552,7 +1558,7 @@ static netdev_tx_t start_xmit(struct sk_buff
>> *skb, struct net_device *dev)
>> ????????? if (!use_napi &&
>> ????????????? unlikely(!virtqueue_enable_cb_delayed(sq->vq))) {
>> ????????????? /* More just got used, free them then recheck. */
>> -??????????? free_old_xmit_skbs(sq);
>> +??????????? free_old_xmit_skbs(sq, txq, false);
>> ????????????? if (sq->vq->num_free >= 2+MAX_SKB_FRAGS) {
>> ????????????????? netif_start_subqueue(dev, qnum);
>> ????????????????? virtqueue_disable_cb(sq->vq);
>> @@ -1560,7 +1566,12 @@ static netdev_tx_t start_xmit(struct sk_buff
>> *skb, struct net_device *dev)
>> ????????? }
>> ????? }
>> ? -??? if (kick || netif_xmit_stopped(txq)) {
>> +??? if (use_napi)
>> +??????? kick = __netdev_tx_sent_queue(txq, bytes, more);
>> +??? else
>> +??????? kick = !more || netif_xmit_stopped(txq);
>> +
>> +??? if (kick) {
>> ????????? if (virtqueue_kick_prepare(sq->vq) &&
>> virtqueue_notify(sq->vq)) {
>> ????????????? u64_stats_update_begin(&sq->stats.syncp);
>> ????????????? sq->stats.kicks++;
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