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Thu, 24 Sep 2020 17:06:52 +0000 From: "Ananyev, Konstantin" To: Honnappa Nagarahalli , "Gujjar, Abhinandan S" , "dev@dpdk.org" , "Doherty, Declan" CC: "jerinj@marvell.com" , "Akhil.goyal@nxp.com" , "Vangati, Narender" , nd , nd Thread-Topic: [dpdk-dev] [v2 1/2] cryptodev: support enqueue callback functions Thread-Index: AQHWhsTbY+pAzzKww0euN2orABmUValrRWzAgAAl9gCAAW0pMIAGJnUAgAAH/lCAAp3uAIAAgn/ggADASgCAASzNQA== Date: Thu, 24 Sep 2020 17:06:52 +0000 Message-ID: References: <1599549024-195051-1-git-send-email-abhinandan.gujjar@intel.com> In-Reply-To: Accept-Language: en-GB, en-US Content-Language: en-US X-MS-Has-Attach: X-MS-TNEF-Correlator: dlp-product: dlpe-windows dlp-reaction: no-action dlp-version: 11.5.1.3 authentication-results: arm.com; dkim=none (message not signed) header.d=none;arm.com; dmarc=none action=none header.from=intel.com; x-originating-ip: [46.7.39.127] x-ms-publictraffictype: Email x-ms-office365-filtering-correlation-id: b5172ab1-a217-48f2-6196-08d860ac3bbe x-ms-traffictypediagnostic: BYAPR11MB3558: x-ld-processed: 46c98d88-e344-4ed4-8496-4ed7712e255d,ExtAddr x-ms-exchange-transport-forked: True x-microsoft-antispam-prvs: x-ms-oob-tlc-oobclassifiers: OLM:10000; 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DIR:OUT; SFP:1102; x-ms-exchange-antispam-messagedata: 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 Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: quoted-printable MIME-Version: 1.0 X-MS-Exchange-CrossTenant-AuthAs: Internal X-MS-Exchange-CrossTenant-AuthSource: BYAPR11MB3301.namprd11.prod.outlook.com X-MS-Exchange-CrossTenant-Network-Message-Id: b5172ab1-a217-48f2-6196-08d860ac3bbe X-MS-Exchange-CrossTenant-originalarrivaltime: 24 Sep 2020 17:06:52.3890 (UTC) X-MS-Exchange-CrossTenant-fromentityheader: Hosted X-MS-Exchange-CrossTenant-id: 46c98d88-e344-4ed4-8496-4ed7712e255d X-MS-Exchange-CrossTenant-mailboxtype: HOSTED X-MS-Exchange-CrossTenant-userprincipalname: sw7GDUA/UApMsbivG4uLWzlkfPdS+IoTbw34rOTqAjIGl7ogekS4B96B4z+4an2NAX/RgK0gKpE0siUaBXUjA5ccp+MEq4iMfoIMHn07kRM= X-MS-Exchange-Transport-CrossTenantHeadersStamped: BYAPR11MB3558 X-OriginatorOrg: intel.com Subject: Re: [dpdk-dev] [v2 1/2] cryptodev: support enqueue callback functions 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" Archived-At: List-Archive: >=20 > > > > > > > > > > > > > > > > > > +#ifdef RTE_CRYPTODEV_CALLBACKS int > > > > > > > > > +rte_cryptodev_rcu_qsbr_add(uint8_t dev_id, struct > > > > > > > > > +rte_rcu_qsbr > > > > > > > > > +*qsbr) { > > > > > > > > > + > > > > > > > > > + struct rte_cryptodev *dev; > > > > > > > > > + > > > > > > > > > + if (!rte_cryptodev_pmd_is_valid_dev(dev_id)) { > > > > > > > > > + CDEV_LOG_ERR("Invalid dev_id=3D%" PRIu8, dev_id); > > > > > > > > > + return -EINVAL; > > > > > > > > > + } > > > > > > > > > + > > > > > > > > > + dev =3D &rte_crypto_devices[dev_id]; > > > > > > > > > + dev->qsbr =3D qsbr; > > > > > > > > > + return 0; > > > > > > > > > +} > > > > > > > > > > > > > > > > So if I understand your patch correctly you propose a new > > > > > > > > working model for > > > > > > > > crypto-devs: > > > > > > > > 1. Control-plane has to allocate/setup rcu_qsbr and do > > > > > > > > rte_cryptodev_rcu_qsbr_add(). > > > > > > > > 2. Data-plane has somehow to obtain pointer to that rcu_qsb= r > > > > > > > > and wrap > > > > > > > > cryptodev_enqueue() > > > > > > > > with rcu_qsbr_quiescent() or > > rcu_qsbr_online()/rcu_qsbr_offline(). > > > > > > > Yes. I think, it is not a new model. It is same as RCU > > > > > > > integration with > > > > LPM. > > > > > > > Please refer: https://patches.dpdk.org/cover/73673/ > > > > > > > > > > > > I am talking about new working model for crypto-dev > > enqueue/dequeue. > > > > > > As I said above now it becomes data-plane thread responsibility= to: > > > > > > -somehow to obtain pointer to that rcu_qsbr for each cryptodev > > > > > > it is > > > > using. > > > > > > -call rcu sync functions (quiescent/online/offline) on a regul= ar basis. > > > > > It is not on regular basis. When data plane comes up, they report= online. > > > > > They report quiescent when they are done with critical section or > > > > > shared > > > > structure. > > > > > > > > I understand that, but it means all existing apps have to be change= d that > > way. > > > > > > > > > All though, there is some dataplane changes involved here, I don'= t > > > > > think, it > > > > is major. > > > > > > > > I still think our goal here should be to make no visible changes to > > > > the dataplane. > > > > I.E. all necessary data-plane changes need to be hidden inside CB > > > > invocation part. > > > Please note that this is being implemented using the memory > > > reclamation framework documented at > > > https://doc.dpdk.org/guides/prog_guide/rcu_lib.html#resource-reclamat= i > > > on-framework-for-dpdk > > > > > > While using RCU there are couple of trade-offs that applications have= to > > consider: > > > 1) Performance - reporting the quiescent state too often results in > > > performance impact on data plane > > > 2) Amount of outstanding memory to reclaim - reporting less often > > > results in more outstanding memory to reclaim > > > > > > Hence, the quiescent state reporting is left to the application. The > > > application decides how often it reports the quiescent state and has = control > > over the data plane performance and the outstanding memory to reclaim. > > > > > > When you say "new working model for crypto-dev enqueue/dequeue", > > > > > > 1) are you comparing these with existing crypto-dev enqueue/dequeue > > APIs? If yes, these are new APIs, it is not breaking anything. > > > 2) are you comparing these with existing call back functions in ethde= v > > > enqueue/dequeue APIs? If yes, agree that this is a new model. But, it= is > > possible to support what ethdev supports along with the RCU method used > > in this patch. > > > > What I am talking about: > > > > Existing cryptodev enqueue/dequeue model doesn't require for the user t= o > > manage any RCU QSBR state manually. > > I believe that addition of ability to add/remove enqueue/dequeue callba= cks > > shouldn't change existing working model. > > I think that adding/removing such callbacks has to be opaque to the use= r DP > > code and shouldn't require user to change it. Same as we have now for > > ethdev callback implementation. > The ethdev callback implementation conveniently leaves the problem of fre= eing memory to the user to resolve, it does not handle the issue. > Hence, it "looks" to be opaque to the DP code. However, if the applicatio= n has to implement a safe way to free the call back memory, its DP > is affected based on call backs are being used or not. Yes, I think that's big drawback in initial ethdev callback implementation = - it simply ignores DP/CP sync problem completely. Though I think it is possible to have both here: keep callback "opaque" to DP code and provide some sync mechanism between = DP/CP. Hopefully one day we can fix ethdev callbacks too.=20 > > I think that forcing DP code to be aware that callbacks are present or = not and > > to modify its behaviour depending on that nearly voids the purpose of h= aving > > callbacks at all. > > In that case DP can just invoke callback function directly from it's co= depath . > > > > > > > > > > > > > > > > > Note that now data-plane thread would have to do that always - > > > > > > even if there are now callbacks installed for that cryptodev qu= eue > > right now. > > > > > > All that changes behaviour of existing apps and I presume would > > > > > > reduce adoption of that fature. > > > If I understand this correct, you are talking about a case where in > > > the application might be registering/unregistering multiple times > > > during its lifetime. In this case, yes, the application might be repo= rting the > > quiescent state even when it has not registered the call backs. But, it= has the > > flexibility to not report it if it implements additional logic. > > > Note that we are assuming that the application has to report quiescen= t > > > state only for using callback functions. Most probably the applicatio= n has > > other requirements to use RCU. > > > Why not support what is done for ethdev call back functions along wit= h > > providing RCU method? > > > > > > > > There is always trade off involved! > > > > > In the previous patch, you suggested that some lazy app may not > > > > > free up the memory allocated by add cb. For such apps, this patch > > > > > has sync mechanism with some additional cost of CP & DP changes. > > > > > > > > Sigh, it is not about laziness of the app. > > > > The problem with current ethedev cb mechanism and yours V1 (which > > > > was just a clone of it) - CP doesn't know when it is safe after CB > > > > removal to free related memory. > > > > > > > > > > I still think all this callback mechanism should be totally > > > > > > opaque to data-plane threads - user shouldn't change his app > > > > > > code depending on would some enqueue/dequeue callbacks be > > installed or not. > > > > > I am not sure, how that can be implemented with existing RCU desi= gn. > > > > > > > > As I said below the simplest way - with calling rcu onine/offline > > > > inside CB invocation block. > > > > That's why I asked you - did you try that approach and what is the > > > > perf numbers? > > > > I presume with no callbacks installed the perf change should be nea= rly > > zero. > > > > > > > > > @Honnappa Nagarahalli, Do you have any suggestions? > > > Reporting quiescent state in the call back functions has several > > disadvantages: > > > 1) it will have performance impacts and the impacts will increase as = the > > number of data plane threads increase. > > > 2) It will require additional configuration parameters to control how > > > often the quiescent state is reported to control the performance impa= ct. > > > 3) Does not take advantage of the fact that most probably the > > > application is using RCU already > > > 4) There are few difficulties as well, please see below. > > > > I suggested Abhinandan to use RCU library because it is already there, = and I > > thought it would be good not to re-implement the wheel. > > Though if you feel librte_rcu doesn't match that task - fine, let's do = it without > > librte_rcu. > > After all, what we need here - just an atomic ref count per queue that = we are > > going to increment at entering and leaving list of callbacks inside > > enqueue/dequeue. > Ok, looks like I missed the point that a queue is used by a single data p= lane thread. > Along with ref count increment you need the memory orderings to avoid rac= e conditions. These will be the same ones used in RCU. > On the control plane, you need to read this counter and poll for the coun= ter updates. All this is same cost as in RCU. Agree. > To control the cost, you > will have to control the rate of quiescent state reporting and might have= to expose this as a configuration parameter. >=20 > The other important information you have to consider is if the thread is = making any blocking calls, which may be in some other library. The > thread is supposed to call rcu_qsbr_thread_offline API before calling a b= locking call. This allows the RCU to know that this particular thread > will not report quiescent state. The cryptodev library might not have tha= t information. >=20 > If you want to go ahead with this design, you can still use RCU with sing= le thread configuration (like you have mentioned below) and hide > the details from the application. Yes, same thought here - use rcu_qsbr online/offline for DP part and hide= actual sync details inside callback code. >=20 > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > That seems quite a big change and I don't think it is > > > > > > > > acceptable for most users. > > > > > > > > From my perspective adding/installing call-backs to the dev > > > > > > > > has to be opaque to the data-plane code. > > > > > > > > Also note that different callbacks can be installed by > > > > > > > > different entities (libs) and might have no idea about each= other. > > > > > > > > That's why I thought it would be better to make all this RC= U > > > > > > > > stuff internal inside cryptodev: > > > > > > > > hide all this rcu_qsbr allocation/setup inside cryptod > > > > > > > > somehow to > > > > > > obtain pointer to that rcu_qsbr ev init/queue setup > > > > > > > > invoke rcu_qsbr_online()/rcu_qsbr_offline() inside > > > > > > cryptodev_enqueue(). > > > This will bring in the application related information such as the th= read ID > > into the library. > > > > I don't think it would. > > Cryptodev enqueue/dequeue functions are not supposed to be thread safe > > (same as rx/tx burst). > > So we can always use RCU with just one thread(thread_id =3D 0). > Agree, the memory that needs to be freed is accessed by a single thread o= n the data plane. RCU with one thread would suffice. >=20 > > But as I said above - if you feel RCU lib is an overhead here, that's f= ine - I > > think it would be easy enough to do without librte_rcu. > > > > > If the same API calls are being made from multiple data plane threads= , > > > you need a way to configure that information to the library. So, it i= s > > > better to leave those details for the application to handle. > > > > > > > > > > I have already tried exploring above stuffs. There are too > > > > > > > many > > > > constraints. > > > > > > > The changes don't fit in, as per RCU design. > > > > > > > > > > > > Hmm could you be more specific here - what constraints are you > > > > > > referring to? > > > > > > > > > > > > > Moreover, having rcu api under enqueue_burst() will affect th= e > > > > > > performance. > > > > > > > > > > > > It most likely will. Though my expectation it will affect > > > > > > performance only when some callbacks are installed. My thought > > here: > > > > > > callback function by itself will affect cryptdev_enqueue > > > > > > performance anyway, > > > > > With existing callback design, I have measured the > > > > > performance(with > > > > crypto perf test) on xeon. > > > > > It was almost negligible and same was shared with Declan. > > > > > > > > I am asking about different thing: did you try alternate approach I > > > > described, that wouldn't require changes in the user data-plane cod= e. > > > > > > > > > That is one of the reasons, I didn't want to add to many stuffs i= n > > > > > to the > > > > callback. > > > > > The best part of existing design is crypto lib is not much modifi= ed. > > > > > The changes are either pushed to CP or DP. > > > > > > > > > > so adding extra overhead for sync is probably ok here. > > > > > > > > I think that extra overhead when callbacks are present is expected > > > > and probably acceptable. > > > > Changes in the upper-layer data-plane code - probably not. > > > > > > > > > > Though for situation when no callbacks are installed - > > > > > > perfomance should be left unaffected (or impact should be as sm= all > > as possible). > > > > > > > > > > > > > The changes are more on control plane side, which is one time= . > > > > > > > The data plane changes are minimal. > > > > > > > > > > > > I still think upper layer data-plane code should stay unaffecte= d > > > > > > (zero changes). > > > > > > > > > > > > > > >=20 >