14. Cryptodev Scheduler Poll Mode Driver Library
Scheduler PMD is a software crypto PMD, which has the capabilities of attaching hardware and/or software cryptodevs, and distributes ingress crypto ops among them in a certain manner.
The Cryptodev Scheduler PMD library (librte_pmd_crypto_scheduler) acts as a software crypto PMD and shares the same API provided by librte_cryptodev. The PMD supports attaching multiple crypto PMDs, software or hardware, as slaves, and distributes the crypto workload to them with certain behavior. The behaviors are categorizes as different “modes”. Basically, a scheduling mode defines certain actions for scheduling crypto ops to its slaves.
The librte_pmd_crypto_scheduler library exports a C API which provides an API for attaching/detaching slaves, set/get scheduling modes, and enable/disable crypto ops reordering.
- Sessionless crypto operation is not supported
- OOP crypto operation is not supported when the crypto op reordering feature is enabled.
To build DPDK with CRYTPO_SCHEDULER_PMD the user is required to set CONFIG_RTE_LIBRTE_PMD_CRYPTO_SCHEDULER=y in config/common_base, and recompile DPDK
To use the PMD in an application, user must:
- Call rte_vdev_init(“crypto_scheduler”) within the application.
- Use –vdev=”crypto_scheduler” in the EAL options, which will call rte_vdev_init() internally.
The following parameters (all optional) can be provided in the previous two calls:
- socket_id: Specify the socket where the memory for the device is going to be allocated (by default, socket_id will be the socket where the core that is creating the PMD is running on).
- max_nb_sessions: Specify the maximum number of sessions that can be created. This value may be overwritten internally if there are too many devices are attached.
- slave: If a cryptodev has been initialized with specific name, it can be attached to the scheduler using this parameter, simply filling the name here. Multiple cryptodevs can be attached initially by presenting this parameter multiple times.
- mode: Specify the scheduling mode of the PMD. The supported scheduling mode parameter values are specified in the “Cryptodev Scheduler Modes Overview” section.
- mode_param: Specify the mode-specific parameter. Some scheduling modes may be initialized with specific parameters other than the default ones, such as the threshold packet size of packet-size-distr mode. This parameter fulfills the purpose.
- ordering: Specify the status of the crypto operations ordering feature. The value of this parameter can be “enable” or “disable”. This feature is disabled by default.
... --vdev "crypto_aesni_mb0,name=aesni_mb_1" --vdev "crypto_aesni_mb1,name=aesni_mb_2" --vdev "crypto_scheduler,slave=aesni_mb_1,slave=aesni_mb_2" ...
- The scheduler cryptodev cannot be started unless the scheduling mode is set and at least one slave is attached. Also, to configure the scheduler in the run-time, like attach/detach slave(s), change scheduling mode, or enable/disable crypto op ordering, one should stop the scheduler first, otherwise an error will be returned.
- The crypto op reordering feature requires using the userdata field of every mbuf to be processed to store temporary data. By the end of processing, the field is set to pointing to NULL, any previously stored value of this field will be lost.
14.4. Cryptodev Scheduler Modes Overview
Currently the Crypto Scheduler PMD library supports following modes of operation:
Initialization mode parameter: round-robin
Round-robin mode, which distributes the enqueued burst of crypto ops among its slaves in a round-robin manner. This mode may help to fill the throughput gap between the physical core and the existing cryptodevs to increase the overall performance.
Initialization mode parameter: packet-size-distr
Packet-size based distribution mode, which works with 2 slaves, the primary slave and the secondary slave, and distributes the enqueued crypto operations to them based on their data lengths. A crypto operation will be distributed to the primary slave if its data length is equal to or bigger than the designated threshold, otherwise it will be handled by the secondary slave.
A typical usecase in this mode is with the QAT cryptodev as the primary and a software cryptodev as the secondary slave. This may help applications to process additional crypto workload than what the QAT cryptodev can handle on its own, by making use of the available CPU cycles to deal with smaller crypto workloads.
The threshold is set to 128 bytes by default. It can be updated by calling function rte_cryptodev_scheduler_option_set. The parameter of option_type must be CDEV_SCHED_OPTION_THRESHOLD and option should point to a rte_cryptodev_scheduler_threshold_option structure filled with appropriate threshold value. Please NOTE this threshold has be a power-of-2 unsigned integer. It is possible to use mode_param initialization parameter to achieve the same purpose. For example:
... –vdev “crypto_scheduler,mode=packet-size-distr,mode_param=threshold:512” ...
The above parameter will overwrite the threshold value to 512.
Initialization mode parameter: fail-over
Fail-over mode, which works with 2 slaves, the primary slave and the secondary slave. In this mode, the scheduler will enqueue the incoming crypto operation burst to the primary slave. When one or more crypto operations fail to be enqueued, then they will be enqueued to the secondary slave.
Initialization mode parameter: multi-core
Multi-core mode, which distributes the workload with several (up to eight) worker cores. The enqueued bursts are distributed among the worker cores in a round-robin manner. If scheduler cannot enqueue entire burst to the same worker, it will enqueue the remaining operations to the next available worker. For pure small packet size (64 bytes) traffic however the multi-core mode is not an optimal solution, as it doesn’t give significant per-core performance improvement. For mixed traffic (IMIX) the optimal number of worker cores is around 2-3. For large packets (1.5 Kbytes) scheduler shows linear scaling in performance up to eight cores. Each worker uses its own slave cryptodev. Only software cryptodevs are supported. Only the same type of cryptodevs should be used concurrently.
The multi-core mode uses one extra parameter:
- corelist: Semicolon-separated list of logical cores to be used as workers. The number of worker cores should be equal to the number of slave cryptodevs. These cores should be present in EAL core list parameter and should not be used by the application or any other process.
- ... –vdev “crypto_aesni_mb1,name=aesni_mb_1” –vdev “crypto_aesni_mb_pmd2,name=aesni_mb_2” –vdev “crypto_scheduler,slave=aesni_mb_1,slave=aesni_mb_2,mode=multi-core,corelist=23;24” ...