09/10/2021 09:41, Narcisa Ana Maria Vasile:
> From: Narcisa Vasile <navas...@microsoft.com>
>
> EAL thread API
>
> **Problem Statement**
> DPDK currently uses the pthread interface to create and manage threads.
> Windows does not support the POSIX thread programming model,
> so it currently
> relies on a header file that hides the Windows calls under
> pthread matched interfaces. Given that EAL should isolate the environment
> specifics from the applications and libraries and mediate
> all the communication with the operating systems, a new EAL interface
> is needed for thread management.
>
> **Goals**
> * Introduce a generic EAL API for threading support that will remove
> the current Windows pthread.h shim.
> * Replace references to pthread_* across the DPDK codebase with the new
> RTE_THREAD_* API.
> * Allow users to choose between using the RTE_THREAD_* API or a
> 3rd party thread library through a configuration option.
>
> **Design plan**
> New API main files:
> * rte_thread.h (librte_eal/include)
> * rte_thread.c (librte_eal/windows)
> * rte_thread.c (librte_eal/common)
Why this file is not in lib/eal/unix/ ?
> **A schematic example of the design**
> --------------------------------------------------
> lib/librte_eal/include/rte_thread.h
> int rte_thread_create();
>
> lib/librte_eal/common/rte_thread.c
> int rte_thread_create()
> {
> return pthread_create();
> }
>
> lib/librte_eal/windows/rte_thread.c
> int rte_thread_create()
> {
> return CreateThread();
> }
> -----------------------------------------------------
We must have the same error code, no matter the underlying implementation.
So you cannot return directly pthread or win32 error codes.
> **Thread attributes**
>
> When or after a thread is created, specific characteristics of the thread
> can be adjusted. Given that the thread characteristics that are of interest
> for DPDK applications are affinity and priority, the following structure
> that represents thread attributes has been defined:
>
> typedef struct
> {
> enum rte_thread_priority priority;
> rte_cpuset_t cpuset;
> } rte_thread_attr_t;
>
> The *rte_thread_create()* function can optionally receive
> an rte_thread_attr_t
> object that will cause the thread to be created with the
> affinity and priority
> described by the attributes object. If no rte_thread_attr_t is passed
> (parameter is NULL), the default affinity and priority are used.
> An rte_thread_attr_t object can also be set to the default values
> by calling *rte_thread_attr_init()*.
>
> *Priority* is represented through an enum that currently advertises
> two values for priority:
> - RTE_THREAD_PRIORITY_NORMAL
> - RTE_THREAD_PRIORITY_REALTIME_CRITICAL
The priority level realtime should never used.
I am not sure about handling the priority so precisely.
I think we can abstract the priority need through different functions.
We already have the function rte_ctrl_thread_create() where priority
should be fixed.
I think we have only 2 types of threads:
- control thread (interrupt, timer, IPC)
- datapath lcore (created in rte_eal_init, including service cores)
It means we need only one new function for datapath thread creation.
> The enum can be extended to allow for multiple priority levels.
> rte_thread_set_priority - sets the priority of a thread
> rte_thread_get_priority - retrieves the priority of a thread
> from the OS
> rte_thread_attr_set_priority - updates an rte_thread_attr_t object
> with a new value for priority
>
> The user can choose thread priority through an EAL parameter,
> when starting an application. If EAL parameter is not used,
> the per-platform default value for thread priority is used.
> Otherwise administrator has an option to set one of available options:
> --thread-prio normal
> --thread-prio realtime
I don't think we need such feature.
Anyway, it is a new feature, so it is beyond the initial replacement goal.
> Example:
> ./dpdk-l2fwd -l 0-3 -n 4 –thread-prio normal -- -q 8 -p ffff
>
> *Affinity* is described by the already known “rte_cpuset_t” type.
> rte_thread_attr_set/get_affinity - sets/gets the affinity field in a
> rte_thread_attr_t object
> rte_thread_set/get_affinity – sets/gets the affinity of a thread
>
> **Errors**
> A translation function that maps Windows error codes to errno-style
> error codes is provided.
>
> **Future work**
> The long term plan is for EAL to provide full threading support:
> * Add support for conditional variables
> * Additional functionality offered by pthread_*
> (such as pthread_setname_np, etc.)
