Messages in this thread | | | Subject | Re: [PATCH RFC 1/2] virtio-net: bql support | From | Jason Wang <> | Date | Thu, 27 Dec 2018 18:04:53 +0800 |
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On 2018/12/26 下午11:22, Michael S. Tsirkin wrote: > On Thu, Dec 06, 2018 at 04:17:36PM +0800, 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 just went over the patch again and I don't understand this comment. > This patch only enabled BQL with tx napi. > > Thus there's no mode switching. > > What did I miss?
Consider the case:
TX NAPI is disabled:
send N packets
turn TX NAPI on:
get tx interrupt
BQL try to consume those packets when lead WARN for dql.
Thanks
> > >> I did it by >> tracking it through skb->cb. And deal with the freeze by reset the BQL >> status. Patch attached. >> >> 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@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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