netdev - Re: [patch net-next v2 00/10] Add support for resource abstraction

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Date:   Tue, 26 Dec 2017 22:05:09 -0600
From:   David Ahern <dsa@...ulusnetworks.com>
To:     Jiri Pirko <jiri@...nulli.us>, netdev@...r.kernel.org,
        davem@...emloft.net
Cc:     arkadis@...lanox.com, mlxsw@...lanox.com, andrew@...n.ch,
        vivien.didelot@...oirfairelinux.com, f.fainelli@...il.com,
        michael.chan@...adcom.com, ganeshgr@...lsio.com,
        saeedm@...lanox.com, matanb@...lanox.com, leonro@...lanox.com,
        idosch@...lanox.com, jakub.kicinski@...ronome.com, ast@...nel.org,
        daniel@...earbox.net, simon.horman@...ronome.com,
        pieter.jansenvanvuuren@...ronome.com, john.hurley@...ronome.com,
        alexander.h.duyck@...el.com, linville@...driver.com,
        gospo@...adcom.com, steven.lin1@...adcom.com, yuvalm@...lanox.com,
        ogerlitz@...lanox.com, roopa@...ulusnetworks.com
Subject: Re: [patch net-next v2 00/10] Add support for resource abstraction

On 12/26/17 5:23 AM, Jiri Pirko wrote:
> From: Jiri Pirko <jiri@...lanox.com>
> 
> Many of the ASIC's internal resources are limited and are shared between
> several hardware procedures. For example, unified hash-based memory can
> be used for many lookup purposes, like FDB and LPM. In many cases the user
> can provide a partitioning scheme for such a resource in order to perform
> fine tuning for his application. In such cases performing driver reload is
> needed for the changes to take place, thus this patchset also adds support
> for hot reload.
> 
> Such an abstraction can be coupled with devlink's dpipe interface, which
> models the ASIC's pipeline as a graph of match/action tables. By modeling
> the hardware resource object, and by coupling it to several dpipe tables,
> further visibility can be achieved in order to debug ASIC-wide issues.
> 
> The proposed interface will provide the user the ability to understand the
> limitations of the hardware, and receive notification regarding its occupancy.
> Furthermore, monitoring the resource occupancy can be done in real-time and
> can be useful in many cases.

In the last RFC (not v1, but RFC) I asked for some kind of description
for each resource, and you and Arkadi have pushed back. Let's walk
through an example to see what I mean:

$ devlink resource show pci/0000:03:00.0
pci/0000:03:00.0:
  name kvd size 245760 size_valid true
  resources:
    name linear size 98304 occ 0
    name hash_double size 60416
    name hash_single size 87040

So this 2700 has 3 resources that can be managed -- some table or
resource or something named 'kvd' with linear, hash_double and
hash_single sub-resources. What are these names referring too? The above
output gives no description, and 'kvd' is not an industry term. Further,
what are these sizes that a user can control? The output contains no
units, no description, nothing. In short, the above output provides
random numbers associated with random names.

I can see dpipe tables exported by this device:

$ devlink dpipe header show pci/0000:03:00.0

pci/0000:03:00.0:
  name mlxsw_meta
  field:
    name erif_port bitwidth 32 mapping_type ifindex
    name l3_forward bitwidth 1
    name l3_drop bitwidth 1
    name adj_index bitwidth 32
    name adj_size bitwidth 32
    name adj_hash_index bitwidth 32

  name ipv6
  field:
    name destination ip bitwidth 128

  name ipv4
  field:
    name destination ip bitwidth 32

  name ethernet
  field:
    name destination mac bitwidth 48

but none mention 'kvd' or 'linear' or 'hash" and none of the other
various devlink options:

$ devlink
Usage: devlink [ OPTIONS ] OBJECT { COMMAND | help }
where  OBJECT := { dev | port | sb | monitor | dpipe }

seem to related to resources.

So how does a user know what they are controlling by this 'resource'
option? Is the user expected to have a PRM or user guide on hand for the
specific device model that is being configured?

Again, I have no objections to kvd, linear, hash, etc terms as they do
relate to Mellanox products. But kvd/linear, for example, does correlate
to industry standard concepts in some way. My request is that the
resource listing guide the user in some way, stating what these
resources mean.

IMO the above output is not user friendly and having to keep a PRM on
hand for each device model is not a realistic solution.