From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-7.0 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, INCLUDES_PATCH,MAILING_LIST_MULTI,SIGNED_OFF_BY,SPF_PASS autolearn=ham autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id DB68AC43387 for ; Sun, 30 Dec 2018 18:48:22 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id A391420836 for ; Sun, 30 Dec 2018 18:48:22 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1726684AbeL3SsV (ORCPT ); Sun, 30 Dec 2018 13:48:21 -0500 Received: from mx1.redhat.com ([209.132.183.28]:40354 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726223AbeL3SsV (ORCPT ); Sun, 30 Dec 2018 13:48:21 -0500 Received: from smtp.corp.redhat.com (int-mx07.intmail.prod.int.phx2.redhat.com [10.5.11.22]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mx1.redhat.com (Postfix) with ESMTPS id 6F9FF80E7B; Sun, 30 Dec 2018 18:48:20 +0000 (UTC) Received: from redhat.com (ovpn-120-135.rdu2.redhat.com [10.10.120.135]) by smtp.corp.redhat.com (Postfix) with ESMTP id A167910018F9; Sun, 30 Dec 2018 18:48:12 +0000 (UTC) Date: Sun, 30 Dec 2018 13:48:12 -0500 From: "Michael S. Tsirkin" To: Jason Wang Cc: linux-kernel@vger.kernel.org, maxime.coquelin@redhat.com, tiwei.bie@intel.com, wexu@redhat.com, jfreimann@redhat.com, "David S. Miller" , virtualization@lists.linux-foundation.org, netdev@vger.kernel.org Subject: Re: [PATCH RFC 1/2] virtio-net: bql support Message-ID: <20181230134539-mutt-send-email-mst@kernel.org> References: <20181205225323.12555-1-mst@redhat.com> <20181205225323.12555-2-mst@redhat.com> <21384cb5-99a6-7431-1039-b356521e1bc3@redhat.com> <20181226102100-mutt-send-email-mst@kernel.org> <620cfd46-aa3e-7eb6-0757-f4afbafda44b@redhat.com> MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline Content-Transfer-Encoding: 8bit In-Reply-To: <620cfd46-aa3e-7eb6-0757-f4afbafda44b@redhat.com> X-Scanned-By: MIMEDefang 2.84 on 10.5.11.22 X-Greylist: Sender IP whitelisted, not delayed by milter-greylist-4.5.16 (mx1.redhat.com [10.5.110.25]); Sun, 30 Dec 2018 18:48:20 +0000 (UTC) Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Thu, Dec 27, 2018 at 06:04:53PM +0800, Jason Wang wrote: > > 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 Can one really switch tx napi on and off? How? While root can change the napi_tx module parameter, I don't think that has any effect outside device probe time. What did I miss? > > > > > > > > > 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 > > > > --- > > > > 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++;