From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: <konstantin.ananyev@intel.com> Received: from mga07.intel.com (mga07.intel.com [134.134.136.100]) by dpdk.org (Postfix) with ESMTP id 0DDC31BBE for <dev@dpdk.org>; Wed, 8 Mar 2017 12:13:45 +0100 (CET) Received: from orsmga004.jf.intel.com ([10.7.209.38]) by orsmga105.jf.intel.com with ESMTP; 08 Mar 2017 03:13:44 -0800 X-ExtLoop1: 1 X-IronPort-AV: E=Sophos;i="5.36,262,1486454400"; d="scan'208";a="65424939" Received: from irsmsx103.ger.corp.intel.com ([163.33.3.157]) by orsmga004.jf.intel.com with ESMTP; 08 Mar 2017 03:13:41 -0800 Received: from irsmsx109.ger.corp.intel.com ([169.254.13.44]) by IRSMSX103.ger.corp.intel.com ([169.254.3.107]) with mapi id 14.03.0248.002; Wed, 8 Mar 2017 11:11:25 +0000 From: "Ananyev, Konstantin" <konstantin.ananyev@intel.com> To: Olivier Matz <olivier.matz@6wind.com> CC: Jan Blunck <jblunck@infradead.org>, "Richardson, Bruce" <bruce.richardson@intel.com>, "dev@dpdk.org" <dev@dpdk.org> Thread-Topic: [dpdk-dev] [RFC 0/8] mbuf: structure reorganization Thread-Index: AQHSdlXOvL8VQlbyOU+/T85mDKip26FcYNGAgA9pHoCAAD0PgIABJAiAgAAukACAAArJAIAEZh4AgAGZsQCAAGmrAIAAB0CAgAAHcgCAAANakIAAIcgAgAARDkCABE1sgIAF9CCAgAABN2CAAAaegIAADv0QgAAJP4CAAAuoYIAAD6MAgACKxICAAuH6gIAJARjw Date: Wed, 8 Mar 2017 11:11:23 +0000 Message-ID: <2601191342CEEE43887BDE71AB9772583FACBF10@IRSMSX109.ger.corp.intel.com> References: <1485271173-13408-1-git-send-email-olivier.matz@6wind.com> <CALe+Z03meh2od13-pfnFh0SpmCqxgKLD5MG2MF5Bj9Q8EtS=Hw@mail.gmail.com> <20170221163808.GA213576@bricha3-MOBL3.ger.corp.intel.com> <CALe+Z01pVFdEckOUabXTnh1q-xEOmJajTagEB1hvqYZazrG7iA@mail.gmail.com> <2601191342CEEE43887BDE71AB9772583F11B4CC@irsmsx105.ger.corp.intel.com> <CALe+Z01ozmTdWwxcc7mG+NhSV16K4+-Pe5uDWASzBBs5oMyh1g@mail.gmail.com> <2601191342CEEE43887BDE71AB9772583F11B633@irsmsx105.ger.corp.intel.com> <20170224150053.279e718d@platinum> <CALe+Z01+K8Odpz3oqk672qsKnjVAXif0TJCwsuPhbcwX+Z11Sg@mail.gmail.com> <2601191342CEEE43887BDE71AB9772583F11E992@irsmsx105.ger.corp.intel.com> <20170228102359.5d601797@platinum> <2601191342CEEE43887BDE71AB9772583F11EA11@irsmsx105.ger.corp.intel.com> <20170228115043.3f78ce52@platinum> <2601191342CEEE43887BDE71AB9772583F11EA96@irsmsx105.ger.corp.intel.com> <20170228132825.37586902@platinum> <2601191342CEEE43887BDE71AB9772583F11EE7A@irsmsx105.ger.corp.intel.com> <20170302174623.268592a7@platinum> In-Reply-To: <20170302174623.268592a7@platinum> Accept-Language: en-IE, en-US Content-Language: en-US X-MS-Has-Attach: X-MS-TNEF-Correlator: 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] [RFC 0/8] mbuf: structure reorganization X-BeenThere: dev@dpdk.org X-Mailman-Version: 2.1.15 Precedence: list List-Id: DPDK patches and discussions <dev.dpdk.org> List-Unsubscribe: <http://dpdk.org/ml/options/dev>, <mailto:dev-request@dpdk.org?subject=unsubscribe> List-Archive: <http://dpdk.org/ml/archives/dev/> List-Post: <mailto:dev@dpdk.org> List-Help: <mailto:dev-request@dpdk.org?subject=help> List-Subscribe: <http://dpdk.org/ml/listinfo/dev>, <mailto:dev-request@dpdk.org?subject=subscribe> X-List-Received-Date: Wed, 08 Mar 2017 11:13:46 -0000 Hi Olivier, >=20 > Hi Konstantin, >=20 > On Tue, 28 Feb 2017 22:53:55 +0000, "Ananyev, Konstantin" <konstantin.ana= nyev@intel.com> wrote: > > > > Another thing that doesn't look very convenient to me here - > > > > We can have 2 different values of timestamp (both normalized and no= t) > > > > and there is no clear way for the application to know which one is = in > > > > use right now. So each app writer would have to come-up with his ow= n > > > > solution. > > > > > > It depends: > > > - the solution you describe is to have the application storing the > > > normalized value in its private metadata. > > > - another solution would be to store the normalized value in > > > m->timestamp. In this case, we would need a flag to tell if the > > > timestamp value is normalized. > > > > My first thought also was about second flag to specify was timestamp > > already normalized or not. > > Though I still in doubt - is it all really worth it: extra ol_flag, new= function in eth_dev API. > > My feeling that we trying to overcomplicate things. >=20 > I don't see what is so complicated. The idea is just to let the > application do the normalization if it is required. I meant 2 ol_flags and special function just to treat properly one of the m= buf field seems too much. Though after second thought might be 2 ol_flags is not a bad idea - it gives PMD writer a freedom to choose provide a normalized or raw value on return from rx_burst().=20 >=20 > If the time is normalized in nanosecond in the PMD, we would still > need to normalized the time reference (the 0). And for that we'd need > a call to a synchronization code as well. >=20 >=20 >=20 > > > The problem pointed out by Jan is that doing the timestamp > > > normalization may take some CPU cycles, even if a small part of packe= ts > > > requires it. > > > > I understand that point, but from what I've seen with real example: > > http://dpdk.org/ml/archives/dev/2016-October/048810.html > > the amount of calculations at RX is pretty small. > > I don't think it would affect performance in a noticeable way > > (though I don't have any numbers here to prove it). >=20 > I think we can consider by default that adding code in the data path > impacts performance. >=20 >=20 > > From other side, if user doesn't want a timestamp he can always disable > > that feature anad save cycles, right? > > > > BTW, you and Jan both mention that not every packet would need a timest= amp. > > Instead we need sort of a timestamp for the group of packets? >=20 > I think that for many applications the timestamp should be as precise > as possible for each packet. >=20 >=20 > > Is that really the only foreseen usage model? >=20 > No, but it could be one. >=20 >=20 > > If so, then why not to have a special function that would extract 'late= st' timestamp > > from the dev? > > Or even have tx_burst_extra() that would return a latest timestamp (ext= ra parameter or so). > > Then there is no need to put timestamp into mbuf at all. >=20 > Doing that will give a poor precision for the timestamp. >=20 >=20 > > > > > Applications that > > > > > are doing this are responsible of what they change. > > > > > > > > > > > > > > > > 3. In theory with eth_dev_detach() - mbuf->port value might be > > > > > > not valid at the point when application would decide to do > > > > > > normalization. > > > > > > > > > > > > So to me all that approach with delayed normalization seems > > > > > > unnecessary overcomplicated. Original one suggested by Olivier, > > > > > > when normalization is done in PMD at RX look much cleaner and > > > > > > more manageable. > > > > > > > > > > Detaching a device requires a synchronization between control and > > > > > data plane, and not only for this use case. > > > > > > > > Of course it does. > > > > But right now it is possible to do: > > > > > > > > eth_rx_burst(port=3D0, ..., &mbuf, 1); > > > > eth_dev_detach(port=3D0, ...); > > > > ... > > > > /*process previously received mbuf */ > > > > > > > > With what you are proposing it would be not always possible any mor= e. > > > > > > With your example, it does not work even without the timestamp featur= e, > > > since the mbuf input port would reference an invalid port. > > > This port is usually used in the application to do a lookup for an p= ort structure, > > > so it is expected that the entry is valid. It would be even worse if = you > > > do a detach + attach. > > > > I am not talking about the mbuf->port value usage. > > Right now user can access/interpret all metadata fields set by PMD RX = routines > > (vlan, rss hash, ol_flags, ptype, etc.) without need to accessing the d= evice data or > > calling device functions. > > With that change it wouldn't be the case anymore. >=20 > That's the same for some other functions. If in my application I want > to call eth_rx_queue_count(m->port), I will have the same problem. Yes, but here you are trying to get extra information about device/queue ba= sed on port value stored inside mbuf. I am talking about information that already stored inside particular mbuf i= tself. About m->port itself - as I said before my preference would be to remove it= at all (partly because of that implication - we can't guarantee that m->port infor= mation would be valid though all mbuf lifetime). But that's probably subject of another discussion.=20 >=20 > I think we also have something quite similar in examples/ptpclient: >=20 > rte_eth_rx_burst(portid, 0, &m, 1); > ... > parse_ptp_frames(portid, m); > ... > ptp_data.portid =3D portid; > ... > rte_eth_timesync_read_tx_timestamp(ptp_data->portid, ...) >=20 >=20 > So, really, I think it's an application issue: when the app deletes > a port, it should ask itself if there are remaining references to > it (m->port). Hmm, and where in the example below do you see the reference to the m->port= ? As I can see, what that the code above does: - it deduces portid value from global variable - not from m->port - saves portid info (not from m->port) inside global variable ptp_data.po= rtid=20 - later inside same function it used that value to call rte_ethdev functio= ns (via parse_fup or parse_drsp). So I am not sure how it relates to the topic we are discussing. Anyway, to summarize how the proposal looks right now:=20 1. m->timestamp value after rx_burst() could be either in raw or normalized= format. 2. validity of m->timesamp and the it's format should be determined by 2 ol= _flags (something like: RX_TIMESTAMP, RX_TIMESTAMP_NORM). 3. PMD is free to choose what timestamp value to return (raw/normalized) =20 4. PMD can provide an optional routine inside devops: uint64_t dev_ops->timestamp_normalise(uint64_t timestamps); =20 5. If the user wants to use that function it would be his responsibility to= map mbuf to the port it was received from.=20 Is that correct? Thanks Konstantin >=20 > > > So, I think it is already the responsibility of the application to do > > > the sync (flush retrieved packets before detaching a port). > > > > The packets are not in RX or TX queue of detaching device any more. > > I received a packet, after that I expect to have all its data and metad= ata inside mbuf. > > So I can store mbufs somewhere and process them much later. > > Or might be I would like to pass it to the secondary process for loggin= g/analyzing, etc. >=20 > Yes, but that's still an app problem for me. >=20 >=20 > > > > >In the first solution, the normalization is > > > > > partial: unit is nanosecond, but the time reference is different. > > > > > > > > Not sure I get you here... > > > > > > In the first solution I described, each PMD had to convert its unit > > > into nanosecond. This is easy because we assume the PMD knows the > > > value of its clock. But to get a fully normalized value, it also has = to > > > use the same time reference, so we would also need to manage an offse= t > > > (we need a new API to give this value to the PMD). > > > > Yes, I suppose we do need an start timestamp and sort of factor() to co= nvert > > HW value, something like: > > > > mbuf->timestamp =3D rxq->start_timestamp + factor(hw_timestamp); > > > > Right? > > Why passing start_timestamp at the configure() phase will be a problem? > > > > > > > > I have another fear related to hardware clocks: if clocks are not > > > synchronized between PMDs, the simple operation "t * ratio - offset" > > > won't work. That's why I think we could delegate this job in a specif= ic > > > library that would manage this. > > > > But then that library would need to account all PMDs inside the system, > > and be aware about each HW clock skew, etc. > > Again, doesn't' sound like an simple task to me. >=20 > Exactly, that's also why I want to let the specialists take care of > it. Having non-normalized timestamps now allow to do the job later > when required, while allowing basic usages as required by metrics > libraries and mlx pmd. >=20 >=20 >=20 > Olivier