Re: [dpdk-dev] [PATCH v16 2/9] eal: add thread attributes

[Thomas Monjalon <thomas@monjalon.net>]

09/11/2021 02:59, Narcisa Ana Maria Vasile:
> On Tue, Oct 12, 2021 at 06:12:21PM +0200, Thomas Monjalon wrote:
> > 09/10/2021 09:41, Narcisa Ana Maria Vasile:
> > > From: Narcisa Vasile <navasile@microsoft.com>
> > > 
> > > Implement thread attributes for:
> > > * thread affinity
> > > * thread priority
> > > Implement functions for managing thread attributes.
> > > 
> > > Priority is represented through an enum that allows for two levels:
> > > 	- RTE_THREAD_PRIORITY_NORMAL
> > > 	- RTE_THREAD_PRIORITY_REALTIME_CRITICAL
> > 
> > It doesn't say how do you translate these priorites in POSIX and win32.
> 
>   I'll send a new version with a better commit message.
>   Thread priorities on both Linux-based and Windows platforms are similarly
>   constructed from a class/policy + priority value. Currently in DPDK, most threads
>   operate at the OS-default priority level but there are cases when increasing the
>   priority is useful. For example, the Mellanox data path acceleration driver requires
>   realtime thread priority. Similarly, some Windows applications will require elevated
>   priority.

It should not. We should not use realtime priority.

>   For these reasons, EAL will advertise 2 priority levels which are named suggestively
>   "normal" and "realtime_critical" and are computed as follows:
> 
>   For Linux and similar platforms:
>     * EAL "normal" priority corresponds to the (default) SCHED_OTHER policy + a priority value of
>       (sched_get_priority_min(SCHED_OTHER) + sched_get_priority_max(SCHED_OTHER))/2.
>       Note that on Linux the resulting priority value will be 0,
>       in accordance to the docs guidance that mention the value should be 0 for SCHED_OTHER policy.
> 	
>     * EAL "realtime" priority corresponds to the SCHED_RR policy + a priority value of 
>       sched_get_priority_max(SCHED_RR);
> 
>   For Windows:
>     * EAL "normal" corresponds to class NORMAL_PRIORITY_CLASS +
>       priority THREAD_PRIORITY_NORMAL
>     * EAL "realtime_critical" corresponds to class REALTIME_PRIORITY_CLASS +
>       priority THREAD_PRIORITY_TIME_CRITICAL