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 04A4BC43387 for ; Wed, 2 Jan 2019 03:29:14 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id BE7192080A for ; Wed, 2 Jan 2019 03:29:13 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1727726AbfABD24 (ORCPT ); Tue, 1 Jan 2019 22:28:56 -0500 Received: from mx1.redhat.com ([209.132.183.28]:41132 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726595AbfABD24 (ORCPT ); Tue, 1 Jan 2019 22:28:56 -0500 Received: from smtp.corp.redhat.com (int-mx03.intmail.prod.int.phx2.redhat.com [10.5.11.13]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mx1.redhat.com (Postfix) with ESMTPS id 2CBB285546; Wed, 2 Jan 2019 03:28:55 +0000 (UTC) Received: from [10.72.12.55] (ovpn-12-55.pek2.redhat.com [10.72.12.55]) by smtp.corp.redhat.com (Postfix) with ESMTPS id 5FEF1608C1; Wed, 2 Jan 2019 03:28:45 +0000 (UTC) Subject: Re: [PATCH RFC 1/2] virtio-net: bql support To: "Michael S. Tsirkin" 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 References: <20181205225323.12555-1-mst@redhat.com> <20181205225323.12555-2-mst@redhat.com> <21384cb5-99a6-7431-1039-b356521e1bc3@redhat.com> <20181226101528-mutt-send-email-mst@kernel.org> <0fa99d9b-e510-d7eb-db1b-831bd7610ce9@redhat.com> <20181230134106-mutt-send-email-mst@kernel.org> From: Jason Wang Message-ID: Date: Wed, 2 Jan 2019 11:28:43 +0800 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:60.0) Gecko/20100101 Thunderbird/60.2.1 MIME-Version: 1.0 In-Reply-To: <20181230134106-mutt-send-email-mst@kernel.org> Content-Type: text/plain; charset=utf-8; format=flowed Content-Transfer-Encoding: 8bit Content-Language: en-US X-Scanned-By: MIMEDefang 2.79 on 10.5.11.13 X-Greylist: Sender IP whitelisted, not delayed by milter-greylist-4.5.16 (mx1.redhat.com [10.5.110.28]); Wed, 02 Jan 2019 03:28:55 +0000 (UTC) Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 2018/12/31 上午2:45, Michael S. Tsirkin wrote: > On Thu, Dec 27, 2018 at 06:00:36PM +0800, Jason Wang wrote: >> On 2018/12/26 下午11:19, 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 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, >>> So how about increasing TSQ pacing shift then? >> >> I can test this. But changing default TCP value is much more than a >> virtio-net specific thing. > Well same logic as wifi applies. Unpredictable latencies related > to radio in one case, to host scheduler in the other. > >>>> 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. >>> I don't think it's reasonable to expect userspace to be that smart ... >>> Why do we need time bounded? used ring is always updated when ring >>> becomes empty. >> >> We don't add used when means BQL may not see the consumed packet in time. >> And the delay varies based on the workload since we count packets not bytes >> or time before doing the batched updating. >> >> Thanks > Sorry I still don't get it. > When nothing is outstanding then we do update the used. > So if BQL stops userspace from sending packets then > we get an interrupt and packets start flowing again. Yes, but how about the cases of multiple flows. That's where I see unstable results. > > It might be suboptimal, we might need to tune it but I doubt running > timers is a solution, timer interrupts cause VM exits. Probably not a timer but a time counter (or event byte counter) in vhost to add used and signal guest if it exceeds a value instead of waiting the number of packets. Thanks > >>>> 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++;