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 6211AC43381 for ; Fri, 22 Mar 2019 15:24:42 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 371E82190A for ; Fri, 22 Mar 2019 15:24:42 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1727298AbfCVPYl (ORCPT ); Fri, 22 Mar 2019 11:24:41 -0400 Received: from mx1.redhat.com ([209.132.183.28]:50036 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726440AbfCVPYk (ORCPT ); Fri, 22 Mar 2019 11:24:40 -0400 Received: from smtp.corp.redhat.com (int-mx05.intmail.prod.int.phx2.redhat.com [10.5.11.15]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mx1.redhat.com (Postfix) with ESMTPS id EDEAC88311; Fri, 22 Mar 2019 15:24:39 +0000 (UTC) Received: from [10.40.205.240] (unknown [10.40.205.240]) by smtp.corp.redhat.com (Postfix) with ESMTP id 7EAD35D70A; Fri, 22 Mar 2019 15:24:38 +0000 (UTC) Subject: Re: [PATCH net-next v3 1/2] net: sched: add empty status flag for NOLOCK qdisc To: Paolo Abeni , netdev@vger.kernel.org Cc: "David S. Miller" , Eric Dumazet , John Fastabend References: <5c30962d8213c8483aee810aa447028e56de963e.1553263445.git.pabeni@redhat.com> From: Ivan Vecera Message-ID: <09c40ed4-b55e-e790-3fe1-83663d0c23bc@redhat.com> Date: Fri, 22 Mar 2019 16:24:37 +0100 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:60.0) Gecko/20100101 Thunderbird/60.5.3 MIME-Version: 1.0 In-Reply-To: <5c30962d8213c8483aee810aa447028e56de963e.1553263445.git.pabeni@redhat.com> Content-Type: text/plain; charset=utf-8; format=flowed Content-Language: en-US Content-Transfer-Encoding: 7bit X-Scanned-By: MIMEDefang 2.79 on 10.5.11.15 X-Greylist: Sender IP whitelisted, not delayed by milter-greylist-4.5.16 (mx1.redhat.com [10.5.110.28]); Fri, 22 Mar 2019 15:24:40 +0000 (UTC) Sender: netdev-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: netdev@vger.kernel.org On 22. 03. 19 16:01, Paolo Abeni wrote: > The queue is marked not empty after acquiring the seqlock, > and it's up to the NOLOCK qdisc clearing such flag on dequeue. > Since the empty status lays on the same cache-line of the > seqlock, it's always hot on cache during the updates. > > This makes the empty flag update a little bit loosy. Given > the lack of synchronization between enqueue and dequeue, this > is unavoidable. > > v2 -> v3: > - qdisc_is_empty() has a const argument (Eric) > > v1 -> v2: > - use really an 'empty' flag instead of 'not_empty', as > suggested by Eric > > Signed-off-by: Paolo Abeni > --- > include/net/sch_generic.h | 11 +++++++++++ > net/sched/sch_generic.c | 3 +++ > 2 files changed, 14 insertions(+) > > diff --git a/include/net/sch_generic.h b/include/net/sch_generic.h > index 31284c078d06..e227475e78ca 100644 > --- a/include/net/sch_generic.h > +++ b/include/net/sch_generic.h > @@ -113,6 +113,9 @@ struct Qdisc { > > spinlock_t busylock ____cacheline_aligned_in_smp; > spinlock_t seqlock; > + > + /* for NOLOCK qdisc, true if there are no enqueued skbs */ > + bool empty; > struct rcu_head rcu; > }; > > @@ -143,11 +146,19 @@ static inline bool qdisc_is_running(struct Qdisc *qdisc) > return (raw_read_seqcount(&qdisc->running) & 1) ? true : false; > } > > +static inline bool qdisc_is_empty(const struct Qdisc *qdisc) > +{ > + if (qdisc->flags & TCQ_F_NOLOCK) > + return qdisc->empty; > + return !qdisc->q.qlen; > +} > + > static inline bool qdisc_run_begin(struct Qdisc *qdisc) > { > if (qdisc->flags & TCQ_F_NOLOCK) { > if (!spin_trylock(&qdisc->seqlock)) > return false; > + qdisc->empty = false; > } else if (qdisc_is_running(qdisc)) { > return false; > } > diff --git a/net/sched/sch_generic.c b/net/sched/sch_generic.c > index a117d9260558..81356ef38d1d 100644 > --- a/net/sched/sch_generic.c > +++ b/net/sched/sch_generic.c > @@ -671,6 +671,8 @@ static struct sk_buff *pfifo_fast_dequeue(struct Qdisc *qdisc) > qdisc_qstats_cpu_backlog_dec(qdisc, skb); > qdisc_bstats_cpu_update(qdisc, skb); > qdisc_qstats_atomic_qlen_dec(qdisc); > + } else { > + qdisc->empty = true; > } > > return skb; > @@ -880,6 +882,7 @@ struct Qdisc *qdisc_alloc(struct netdev_queue *dev_queue, > sch->enqueue = ops->enqueue; > sch->dequeue = ops->dequeue; > sch->dev_queue = dev_queue; > + sch->empty = true; > dev_hold(dev); > refcount_set(&sch->refcnt, 1); > > Reviewed-by: Ivan Vecera