netdev - Re: [RFC PATCH] net: introduce HW Rate Limiting Driver API

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Date: Wed, 05 Jun 2024 17:52:32 +0200
From: Paolo Abeni <pabeni@...hat.com>
To: Cosmin Ratiu <cratiu@...dia.com>, "netdev@...r.kernel.org"
	 <netdev@...r.kernel.org>
Cc: "jhs@...atatu.com" <jhs@...atatu.com>, "sridhar.samudrala@...el.com"
 <sridhar.samudrala@...el.com>, "john.fastabend@...il.com"
 <john.fastabend@...il.com>, "madhu.chittim@...el.com"
 <madhu.chittim@...el.com>,  "jiri@...nulli.us" <jiri@...nulli.us>,
 "horms@...nel.org" <horms@...nel.org>,  "sgoutham@...vell.com"
 <sgoutham@...vell.com>, "kuba@...nel.org" <kuba@...nel.org>
Subject: Re: [RFC PATCH] net: introduce HW Rate Limiting Driver API

On Wed, 2024-06-05 at 15:04 +0000, Cosmin Ratiu wrote:
> On Wed, 2024-05-08 at 22:20 +0200, Paolo Abeni wrote:
> 
> > +/**
> > + * struct net_shaper_info - represents a shaping node on the NIC H/W
> > + * @metric: Specify if the bw limits refers to PPS or BPS
> > + * @bw_min: Minimum guaranteed rate for this shaper
> > + * @bw_max: Maximum peak bw allowed for this shaper
> > + * @burst: Maximum burst for the peek rate of this shaper
> > + * @priority: Scheduling priority for this shaper
> > + * @weight: Scheduling weight for this shaper
> > + */
> > +struct net_shaper_info {
> > +	enum net_shaper_metric metric;
> > +	u64 bw_min;	/* minimum guaranteed bandwidth, according to metric */
> > +	u64 bw_max;	/* maximum allowed bandwidth */
> > +	u32 burst;	/* maximum burst in bytes for bw_max */
> 
> 'burst' really should be u64 if it can deal with bytes. In a 400Gbps
> link, u32 really is peanuts.
> 
> > +/**
> > + * enum net_shaper_scope - the different scopes where a shaper could be attached
> > + * @NET_SHAPER_SCOPE_PORT:   The root shaper for the whole H/W.
> > + * @NET_SHAPER_SCOPE_NETDEV: The main shaper for the given network device.
> > + * @NET_SHAPER_SCOPE_VF:     The shaper is attached to the given virtual
> > + * function.
> > + * @NET_SHAPER_SCOPE_QUEUE_GROUP: The shaper groups multiple queues under the
> > + * same device.
> > + * @NET_SHAPER_SCOPE_QUEUE:  The shaper is attached to the given device queue.
> > + *
> > + * NET_SHAPER_SCOPE_PORT and NET_SHAPER_SCOPE_VF are only available on
> > + * PF devices, usually inside the host/hypervisor.
> > + * NET_SHAPER_SCOPE_NETDEV, NET_SHAPER_SCOPE_QUEUE_GROUP and
> > + * NET_SHAPER_SCOPE_QUEUE are available on both PFs and VFs devices.
> > + */
> > +enum net_shaper_scope {
> > +	NET_SHAPER_SCOPE_PORT,
> > +	NET_SHAPER_SCOPE_NETDEV,
> > +	NET_SHAPER_SCOPE_VF,
> > +	NET_SHAPER_SCOPE_QUEUE_GROUP,
> > +	NET_SHAPER_SCOPE_QUEUE,
> > +};
> 
> How would modelling groups of VFs (as implemented in [1]) look like
> with this proposal?
> I could imagine a NET_SHAPER_SCOPE_VF_GROUP scope, with a shared shaper
> across multiple VFs. 

Following-up yday reviewer mtg - which was spent mainly on this topic -
- the current direction is to replace NET_SHAPER_SCOPE_QUEUE_GROUP with
a more generic 'scope', grouping of either queues, VF/netdev or even
other groups (allowing nesting).

> How would managing membership of VFs in a group
> look like? Will the devlink API continue to be used for that? Or will
> something else be introduced?

The idea is to introduce a new generic netlink interface, yaml-based,
to expose these features to user-space.

> Looking a bit into the future now...
> I am nowadays thinking about extending the mlx5 VF group rate limit
> feature to support VFs from multiple PFs from the same NIC (the
> hardware can be configured to use a shared shaper across multiple
> ports), how could that feature be represented in this API, given that
> ops relate to a netdevice? Which netdevice should be used for this
> scenario?

I must admit we[1] haven't thought yet about the scenario you describe
above. I guess we could encode the PF number and the VF number in the
handle major/minor and operate on any PF device belonging to the same
silicon, WDYT?

Thanks,

Paolo

[1] or at least myself;)