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=-16.8 required=3.0 tests=BAYES_00, HEADER_FROM_DIFFERENT_DOMAINS,INCLUDES_CR_TRAILER,INCLUDES_PATCH, MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS,USER_AGENT_GIT 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 1B26EC433E0 for ; Mon, 15 Mar 2021 03:10:40 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id DFA1360C41 for ; Mon, 15 Mar 2021 03:10:39 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S229806AbhCODKJ (ORCPT ); Sun, 14 Mar 2021 23:10:09 -0400 Received: from szxga05-in.huawei.com ([45.249.212.191]:13533 "EHLO szxga05-in.huawei.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S229778AbhCODJr (ORCPT ); Sun, 14 Mar 2021 23:09:47 -0400 Received: from DGGEMS412-HUB.china.huawei.com (unknown [172.30.72.60]) by szxga05-in.huawei.com (SkyGuard) with ESMTP id 4DzLtr1WmmzNn1Q; Mon, 15 Mar 2021 11:07:16 +0800 (CST) Received: from localhost.localdomain (10.69.192.56) by DGGEMS412-HUB.china.huawei.com (10.3.19.212) with Microsoft SMTP Server id 14.3.498.0; Mon, 15 Mar 2021 11:09:36 +0800 From: Yunsheng Lin To: , , CC: , , , , , , , , , , , Subject: [RFC v2] net: sched: implement TCQ_F_CAN_BYPASS for lockless qdisc Date: Mon, 15 Mar 2021 11:10:18 +0800 Message-ID: <1615777818-13969-1-git-send-email-linyunsheng@huawei.com> X-Mailer: git-send-email 2.7.4 In-Reply-To: <1615603667-22568-1-git-send-email-linyunsheng@huawei.com> References: <1615603667-22568-1-git-send-email-linyunsheng@huawei.com> MIME-Version: 1.0 Content-Type: text/plain X-Originating-IP: [10.69.192.56] X-CFilter-Loop: Reflected Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Currently pfifo_fast has both TCQ_F_CAN_BYPASS and TCQ_F_NOLOCK flag set, but queue discipline by-pass does not work for lockless qdisc because skb is always enqueued to qdisc even when the qdisc is empty, see __dev_xmit_skb(). This patch calls sch_direct_xmit() to transmit the skb directly to the driver for empty lockless qdisc too, which aviod enqueuing and dequeuing operation. qdisc->empty is set to false whenever a skb is enqueued, see pfifo_fast_enqueue(), and is set to true when skb dequeuing return NULL, see pfifo_fast_dequeue(), a spinlock is added to avoid the race between enqueue/dequeue and qdisc->empty setting. If there is requeued skb in q->gso_skb, and qdisc->empty is true, do not allow bypassing requeued skb. enqueuing and dequeuing in q->gso_skb is always protected by qdisc->seqlock, so is the access of q->gso_skb by skb_queue_empty(); Also, qdisc is scheduled at the end of qdisc_run_end() when q->empty is false to avoid packet stuck problem. The performance for ip_forward test increases about 10% with this patch. Signed-off-by: Yunsheng Lin --- RFC V2: fix requeued skb out of order and data race problem. --- include/net/pkt_sched.h | 2 ++ include/net/sch_generic.h | 7 +++++-- net/core/dev.c | 14 ++++++++++++++ net/sched/sch_generic.c | 31 ++++++++++++++++++++++++++++++- 4 files changed, 51 insertions(+), 3 deletions(-) diff --git a/include/net/pkt_sched.h b/include/net/pkt_sched.h index f5c1bee..c760f6a 100644 --- a/include/net/pkt_sched.h +++ b/include/net/pkt_sched.h @@ -122,6 +122,8 @@ void qdisc_warn_nonwc(const char *txt, struct Qdisc *qdisc); bool sch_direct_xmit(struct sk_buff *skb, struct Qdisc *q, struct net_device *dev, struct netdev_queue *txq, spinlock_t *root_lock, bool validate); +bool sch_may_need_requeuing(struct sk_buff *skb, struct Qdisc *q, + struct net_device *dev); void __qdisc_run(struct Qdisc *q); diff --git a/include/net/sch_generic.h b/include/net/sch_generic.h index 2d6eb60..6591356 100644 --- a/include/net/sch_generic.h +++ b/include/net/sch_generic.h @@ -161,7 +161,6 @@ static inline bool qdisc_run_begin(struct Qdisc *qdisc) if (qdisc->flags & TCQ_F_NOLOCK) { if (!spin_trylock(&qdisc->seqlock)) return false; - WRITE_ONCE(qdisc->empty, false); } else if (qdisc_is_running(qdisc)) { return false; } @@ -176,8 +175,12 @@ static inline bool qdisc_run_begin(struct Qdisc *qdisc) static inline void qdisc_run_end(struct Qdisc *qdisc) { write_seqcount_end(&qdisc->running); - if (qdisc->flags & TCQ_F_NOLOCK) + if (qdisc->flags & TCQ_F_NOLOCK) { spin_unlock(&qdisc->seqlock); + + if (unlikely(!READ_ONCE(qdisc->empty))) + __netif_schedule(qdisc); + } } static inline bool qdisc_may_bulk(const struct Qdisc *qdisc) diff --git a/net/core/dev.c b/net/core/dev.c index 2bfdd52..8f4afb6 100644 --- a/net/core/dev.c +++ b/net/core/dev.c @@ -3791,6 +3791,20 @@ static inline int __dev_xmit_skb(struct sk_buff *skb, struct Qdisc *q, qdisc_calculate_pkt_len(skb, q); if (q->flags & TCQ_F_NOLOCK) { + if (q->flags & TCQ_F_CAN_BYPASS && READ_ONCE(q->empty) && + qdisc_run_begin(q)) { + qdisc_bstats_cpu_update(q, skb); + + if (sch_may_need_requeuing(skb, q, dev)) + __qdisc_run(q); + else if (sch_direct_xmit(skb, q, dev, txq, NULL, true) && + !READ_ONCE(q->empty)) + __qdisc_run(q); + + qdisc_run_end(q); + return NET_XMIT_SUCCESS; + } + rc = q->enqueue(skb, q, &to_free) & NET_XMIT_MASK; qdisc_run(q); diff --git a/net/sched/sch_generic.c b/net/sched/sch_generic.c index 49eae93..0df1462 100644 --- a/net/sched/sch_generic.c +++ b/net/sched/sch_generic.c @@ -273,6 +273,23 @@ static struct sk_buff *dequeue_skb(struct Qdisc *q, bool *validate, return skb; } +bool sch_may_need_requeuing(struct sk_buff *skb, struct Qdisc *q, + struct net_device *dev) +{ + bool again = false; + + if (likely(skb_queue_empty(&q->gso_skb))) + return false; + + /* need validating before requeuing */ + skb = validate_xmit_skb_list(skb, dev, &again); + if (unlikely(!skb)) + return true; + + dev_requeue_skb(skb, q); + return true; +} + /* * Transmit possibly several skbs, and handle the return status as * required. Owning running seqcount bit guarantees that @@ -606,6 +623,11 @@ static const u8 prio2band[TC_PRIO_MAX + 1] = { */ struct pfifo_fast_priv { struct skb_array q[PFIFO_FAST_BANDS]; + + /* protect against data race between enqueue/dequeue and + * qdisc->empty setting + */ + spinlock_t lock; }; static inline struct skb_array *band2list(struct pfifo_fast_priv *priv, @@ -623,7 +645,10 @@ static int pfifo_fast_enqueue(struct sk_buff *skb, struct Qdisc *qdisc, unsigned int pkt_len = qdisc_pkt_len(skb); int err; - err = skb_array_produce(q, skb); + spin_lock(&priv->lock); + err = __ptr_ring_produce(&q->ring, skb); + WRITE_ONCE(qdisc->empty, false); + spin_unlock(&priv->lock); if (unlikely(err)) { if (qdisc_is_percpu_stats(qdisc)) @@ -642,6 +667,7 @@ static struct sk_buff *pfifo_fast_dequeue(struct Qdisc *qdisc) struct sk_buff *skb = NULL; int band; + spin_lock(&priv->lock); for (band = 0; band < PFIFO_FAST_BANDS && !skb; band++) { struct skb_array *q = band2list(priv, band); @@ -655,6 +681,7 @@ static struct sk_buff *pfifo_fast_dequeue(struct Qdisc *qdisc) } else { WRITE_ONCE(qdisc->empty, true); } + spin_unlock(&priv->lock); return skb; } @@ -739,6 +766,8 @@ static int pfifo_fast_init(struct Qdisc *qdisc, struct nlattr *opt, /* Can by-pass the queue discipline */ qdisc->flags |= TCQ_F_CAN_BYPASS; + + spin_lock_init(&priv->lock); return 0; } -- 2.7.4