From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from dpdk.org (dpdk.org [92.243.14.124]) by inbox.dpdk.org (Postfix) with ESMTP id A071CA2EEB for ; Mon, 7 Oct 2019 11:01:23 +0200 (CEST) Received: from [92.243.14.124] (localhost [127.0.0.1]) by dpdk.org (Postfix) with ESMTP id A233A1C22D; Mon, 7 Oct 2019 11:01:20 +0200 (CEST) Received: from mga05.intel.com (mga05.intel.com [192.55.52.43]) by dpdk.org (Postfix) with ESMTP id 8B8731C1C5 for ; Mon, 7 Oct 2019 11:01:18 +0200 (CEST) X-Amp-Result: SKIPPED(no attachment in message) X-Amp-File-Uploaded: False Received: from fmsmga003.fm.intel.com ([10.253.24.29]) by fmsmga105.fm.intel.com with ESMTP/TLS/DHE-RSA-AES256-GCM-SHA384; 07 Oct 2019 02:01:17 -0700 X-ExtLoop1: 1 X-IronPort-AV: E=Sophos;i="5.67,267,1566889200"; d="scan'208";a="199469888" Received: from irsmsx153.ger.corp.intel.com ([163.33.192.75]) by FMSMGA003.fm.intel.com with ESMTP; 07 Oct 2019 02:01:15 -0700 Received: from irsmsx155.ger.corp.intel.com (163.33.192.3) by IRSMSX153.ger.corp.intel.com (163.33.192.75) with Microsoft SMTP Server (TLS) id 14.3.439.0; Mon, 7 Oct 2019 10:01:15 +0100 Received: from irsmsx105.ger.corp.intel.com ([169.254.7.164]) by irsmsx155.ger.corp.intel.com ([169.254.14.139]) with mapi id 14.03.0439.000; Mon, 7 Oct 2019 10:01:15 +0100 From: "Ananyev, Konstantin" To: Honnappa Nagarahalli , "stephen@networkplumber.org" , "paulmck@linux.ibm.com" CC: "Wang, Yipeng1" , "Medvedkin, Vladimir" , "Ruifeng Wang (Arm Technology China)" , Dharmik Thakkar , "dev@dpdk.org" , nd , nd Thread-Topic: [PATCH v3 1/3] lib/ring: add peek API Thread-Index: AQHVeCGUIgBwOBQCI0OY47a7OfyurKdHoInwgAGlroCABaC3MA== Date: Mon, 7 Oct 2019 09:01:14 +0000 Message-ID: <2601191342CEEE43887BDE71AB9772580191971EBE@irsmsx105.ger.corp.intel.com> References: <20190906094534.36060-1-ruifeng.wang@arm.com> <20191001062917.35578-1-honnappa.nagarahalli@arm.com> <20191001062917.35578-2-honnappa.nagarahalli@arm.com> <2601191342CEEE43887BDE71AB9772580191970014@irsmsx105.ger.corp.intel.com> In-Reply-To: Accept-Language: en-IE, en-US Content-Language: en-US X-MS-Has-Attach: X-MS-TNEF-Correlator: x-titus-metadata-40: eyJDYXRlZ29yeUxhYmVscyI6IiIsIk1ldGFkYXRhIjp7Im5zIjoiaHR0cDpcL1wvd3d3LnRpdHVzLmNvbVwvbnNcL0ludGVsMyIsImlkIjoiYjk5YjU5YzgtNmRlYS00N2I5LWEwOTctY2Y4ODJkYjU2Y2MzIiwicHJvcHMiOlt7Im4iOiJDVFBDbGFzc2lmaWNhdGlvbiIsInZhbHMiOlt7InZhbHVlIjoiQ1RQX05UIn1dfV19LCJTdWJqZWN0TGFiZWxzIjpbXSwiVE1DVmVyc2lvbiI6IjE3LjEwLjE4MDQuNDkiLCJUcnVzdGVkTGFiZWxIYXNoIjoiWE44RHRTenZWYU9uTXM3MXRPczBWSk96OXNOVnB5SUpiXC85ekVvOUZTckI2dmhPc1pITjdDVERkdTJSMktIT2wifQ== x-ctpclassification: CTP_NT dlp-product: dlpe-windows dlp-version: 11.2.0.6 dlp-reaction: no-action x-originating-ip: [163.33.239.180] Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: quoted-printable MIME-Version: 1.0 Subject: Re: [dpdk-dev] [PATCH v3 1/3] lib/ring: add peek API X-BeenThere: dev@dpdk.org X-Mailman-Version: 2.1.15 Precedence: list List-Id: DPDK patches and discussions List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Errors-To: dev-bounces@dpdk.org Sender: "dev" >=20 > > > Subject: [PATCH v3 1/3] lib/ring: add peek API > > > > > > From: Ruifeng Wang > > > > > > The peek API allows fetching the next available object in the ring > > > without dequeuing it. This helps in scenarios where dequeuing of > > > objects depend on their value. > > > > > > Signed-off-by: Dharmik Thakkar > > > Signed-off-by: Ruifeng Wang > > > Reviewed-by: Honnappa Nagarahalli > > > Reviewed-by: Gavin Hu > > > --- > > > lib/librte_ring/rte_ring.h | 30 ++++++++++++++++++++++++++++++ > > > 1 file changed, 30 insertions(+) > > > > > > diff --git a/lib/librte_ring/rte_ring.h b/lib/librte_ring/rte_ring.h > > > index 2a9f768a1..d3d0d5e18 100644 > > > --- a/lib/librte_ring/rte_ring.h > > > +++ b/lib/librte_ring/rte_ring.h > > > @@ -953,6 +953,36 @@ rte_ring_dequeue_burst(struct rte_ring *r, void > > **obj_table, > > > r->cons.single, available); > > > } > > > > > > +/** > > > + * Peek one object from a ring. > > > + * > > > + * The peek API allows fetching the next available object in the rin= g > > > + * without dequeuing it. This API is not multi-thread safe with > > > +respect > > > + * to other consumer threads. > > > + * > > > + * @param r > > > + * A pointer to the ring structure. > > > + * @param obj_p > > > + * A pointer to a void * pointer (object) that will be filled. > > > + * @return > > > + * - 0: Success, object available > > > + * - -ENOENT: Not enough entries in the ring. > > > + */ > > > +__rte_experimental > > > +static __rte_always_inline int > > > +rte_ring_peek(struct rte_ring *r, void **obj_p) > > > > As it is not MT safe, then I think we need _sc_ in the name, to follow = other > > rte_ring functions naming conventions > > (rte_ring_sc_peek() or so). > Agree >=20 > > > > As a better alternative what do you think about introducing a serialize= d > > versions of DPDK rte_ring dequeue functions? > > Something like that: > > > > /* same as original ring dequeue, but: > > * 1) move cons.head only if cons.head =3D=3D const.tail > > * 2) don't update cons.tail > > */ > > unsigned int > > rte_ring_serial_dequeue_bulk(struct rte_ring *r, void **obj_table, unsi= gned > > int n, > > unsigned int *available); > > > > /* sets both cons.head and cons.tail to cons.head + num */ void > > rte_ring_serial_dequeue_finish(struct rte_ring *r, uint32_t num); > > > > /* resets cons.head to const.tail value */ void > > rte_ring_serial_dequeue_abort(struct rte_ring *r); > > > > Then your dq_reclaim cycle function will look like that: > > > > const uint32_t nb_elt =3D dq->elt_size/8 + 1; uint32_t avl, n; uintptr= _t > > elt[nb_elt]; ... > > > > do { > > > > /* read next elem from the queue */ > > n =3D rte_ring_serial_dequeue_bulk(dq->r, elt, nb_elt, &avl); > > if (n =3D=3D 0) > > break; > > > > /* wrong period, keep elem in the queue */ if (rte_rcu_qsbr_check(dr-= >v, > > elt[0]) !=3D 1) { > > rte_ring_serial_dequeue_abort(dq->r); > > break; > > } > > > > /* can reclaim, remove elem from the queue */ > > rte_ring_serial_dequeue_finish(dr->q, nb_elt); > > > > /*call reclaim function */ > > dr->f(dr->p, elt); > > > > } while (avl >=3D nb_elt); > > > > That way, I think even rte_rcu_qsbr_dq_reclaim() can be MT safe. > > As long as actual reclamation callback itself is MT safe of course. >=20 > I think it is a great idea. The other writers would still be polling for = the current writer to update the tail or update the head. This makes it a > blocking solution. Yep, it is a blocking one. > We can make the other threads not poll i.e. they will quit reclaiming if = they see that other writers are dequeuing from the queue.=20 Actually didn't think about that possibility, but yes should be possible to= have _try_ semantics too.=20 >The other way is to use per thread queues. >=20 > The other requirement I see is to support unbounded-size data structures = where in the data structures do not have a pre-determined > number of entries. Also, currently the defer queue size is equal to the t= otal number of entries in a given data structure. There are plans to > support dynamically resizable defer queue. This means, memory allocation = which will affect the lock-free-ness of the solution. >=20 > So, IMO: > 1) The API should provide the capability to support different algorithms = - may be through some flags? > 2) The requirements for the ring are pretty unique to the problem we have= here (for ex: move the cons-head only if cons-tail is also the > same, skip polling). So, we should probably implement a ring with-in the = RCU library? Personally, I think such serialization ring API would be useful for other c= ases too. There are few cases when user need to read contents of the queue without re= moving elements from it. Let say we do use similar approach inside TLDK to implement TCP transmit qu= eue. If such API would exist in DPDK we can just use it straightway, without mai= ntaining a separate one. >=20 > From the timeline perspective, adding all these capabilities would be dif= ficult to get done with in 19.11 timeline. What I have here satisfies > my current needs. I suggest that we make provisions in APIs now to suppor= t all these features, but do the implementation in the coming > releases. Does this sound ok for you? Not sure I understand your suggestion here... Could you explain it a bit more - how new API will look like and what would= be left for the future.=20 >=20 > > > > > +{ > > > + uint32_t prod_tail =3D r->prod.tail; > > > + uint32_t cons_head =3D r->cons.head; > > > + uint32_t count =3D (prod_tail - cons_head) & r->mask; > > > + unsigned int n =3D 1; > > > + if (count) { > > > + DEQUEUE_PTRS(r, &r[1], cons_head, obj_p, n, void *); > > > + return 0; > > > + } > > > + return -ENOENT; > > > +} > > > + > > > #ifdef __cplusplus > > > } > > > #endif > > > -- > > > 2.17.1