RE: [RFC] dmadev: add QoS capability

[Vamsi Krishna Attunuru <vattunuru@marvell.com>]

>-----Original Message-----
>From: Morten Brørup <mb@smartsharesystems.com>
>Sent: Monday, July 29, 2024 7:23 PM
>To: Bruce Richardson <bruce.richardson@intel.com>
>Cc: Vamsi Krishna Attunuru <vattunuru@marvell.com>;
>fengchengwen@huawei.com; dev@dpdk.org; kevin.laatz@intel.com; Jerin
>Jacob <jerinj@marvell.com>; Anoob Joseph <anoobj@marvell.com>
>Subject: [EXTERNAL] RE: [RFC] dmadev: add QoS capability
>
>> From: Bruce Richardson [mailto: bruce. richardson@ intel. com] > Sent:
>> Monday, 29 July 2024 15. 27 > > On Mon, Jul 29, 2024 at 03: 14: 55PM
>> +0200, Morten Brørup wrote: > > > From: Vamsi Attunuru [mailto: 
>> vattunuru@ marvell. com]
>
>> From: Bruce Richardson [mailto:bruce.richardson@intel.com]
>> Sent: Monday, 29 July 2024 15.27
>>
>> On Mon, Jul 29, 2024 at 03:14:55PM +0200, Morten Brørup wrote:
>> > > From: Vamsi Attunuru [mailto:vattunuru@marvell.com]
>> > > Sent: Monday, 29 July 2024 13.56
>> > >
>> > > Some DMA controllers support QoS at HW command queue level to
>> > > differentiate the performance on different HW queues based on the
>> > > priority configured. Patch adds required fields in dmadev
>> > > structures to get hardware supported priority levels and the
>> > > provision to configure the priority from the applications.
>> >
>> > Do we foresee anything more advanced than Strict Priority scheduling
>> > for DMA
>> anytime in the future?
>> >
>> > If not, then consider calling this new capability Prioritization
>> > (CAPA_PRIO)
>> instead of Quality Of Service (CAPA_QOS). Then we don't need to add
>> and describe QoS parameters for a more advanced QoS scheduling
>> algorithm (e.g. the "weight" for weighted fair queueing).
>> >
>>
>> There could be more than just regular prioritization settings
>> involved, so I think it's best to leave some options open. Even with
>> just a "prioritization" setting, it could be used as a weighting vs strict priority.
>> Question is whether in such a case - of a single-value number for high
>> vs low priority - it's better to explicitly separate out a weight
>> priority vs a strict priority, or give a simpler interface by allowing
>> just a single number value.
>
>If we leave some options open, we need to define the API for them.
>Let's not go overboard with this, but stay within what could be realistic for a
>DMA engine.
>
>Remember, the API needs to be cross-platform, so simply replacing the
>"Priority" parameter with a "QoS Class ID" also requires adding configuration
>parameters to map each QoS Class ID to a generically defined behavior (e.g.
>priority, weight).
>
>@Vamsi, how many priority levels does your DMA hardware support?

Hi Morten & Bruce, thanks for the comments.

Our DMA HW supports 4 priorities. Yes, as Bruce pointed, we can have options
open to support both(weighted & strict). Let me get back on this that could be
sensible for DMA kind of hardware.

Regards
Vamsi