Date:   Thu, 6 Dec 2018 16:31:24 +0800
From:   Jason Wang <jasowang@...hat.com>
To:     "Michael S. Tsirkin" <mst@...hat.com>, linux-kernel@...r.kernel.org
Cc:     netdev@...r.kernel.org, virtualization@...ts.linux-foundation.org,
        maxime.coquelin@...hat.com, wexu@...hat.com,
        "David S. Miller" <davem@...emloft.net>
Subject: Re: [PATCH RFC 1/2] virtio-net: bql support


On 2018/12/6 下午4:17, Jason Wang wrote:
>
> On 2018/12/6 上午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@...hat.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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View attachment "0001-virtio-net-byte-queue-limit-support.patch" of type "text/x-patch" (4779 bytes)

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