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

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Date:   Thu, 4 Jan 2018 08:58:41 -0700
From:   David Ahern <dsa@...ulusnetworks.com>
To:     Arkadi Sharshevsky <arkadis@...lanox.com>,
        Jiri Pirko <jiri@...nulli.us>, netdev@...r.kernel.org,
        roopa@...ulusnetworks.com
Cc:     davem@...emloft.net, 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
Subject: Re: [patch net-next v2 00/10] Add support for resource abstraction

On 1/4/18 2:24 AM, Arkadi Sharshevsky wrote:
>> Again, my comments all stem from user experience.
>>
>> Can you explain what "double_word" means for a unit? I would expect a
>> units to be kB or count (or items or entries).
>>
> 
> Double word is 64 bit, dont understand why this is confusing.

As Andrew pointed out, double word can have a range of sizes.

To my point here, a 'unit' for a number should not be the number of bits
it is represented by. I believe all of the kvd sizes are in entries
(ie., a linear size of 98304 means I can have 98,304 entries in that
resource).

> 
>> $ devlink resource show pci/0000:03:00.0
>> pci/0000:03:00.0:
>>   name kvd size 245760 unit double_word size_valid true
>>   resources:
>>     name linear size 98304 occ 0 unit double_word
>>     name hash_double size 60416 unit double_word
>>     name hash_single size 87040 unit double_word
>>
>> While that is confusing here from the userspace command it goes hand in
>> hand with patch 2 and:
>>
>> +enum devlink_resource_unit {
>> +	DEVLINK_RESOURCE_UNIT_DOUBLE_WORD,
>> +};
>>
>>
>> Also, it seems like the occ of 0 is wrong since we know from past
>> responses that if I set linear to 0 all of networking breaks.
> 
> You are clearly misunderstanding what is occupancy of the resource
> and what kvd linear is good for. As I mentioned in the last response
> kvd linear is mapped to adjacency table. So in case its 0 no nexthop
> routes could be configured, this information is provided by the
> dpipe<-->resource.
> 
> Occupancy means how much of the resource is used right now, why is
> this wrong? and how its related to the size 0 exactly?

The summary line above shows the current kvd/linear occupancy is '0'.
That suggests my L3 only deployment is not using any kvd/linear which
means I can set its allocation to 0 and devote more kvd resources to the
hash regions.

But, as I pointed out in previous responses I can not set linear to 0.
If I do all of networking breaks. That suggests that kvd/linear is used
by more networking entities than you are currently reporting. Hence,
telling me the kvd/linear occupancy is 0 is wrong.

I believe the stems from the how you are determining occupancy and the
fact that not all tables have been implemented. Showing the current
occupancy of a resource is very helpful, so it should be part of the API.

However, until mlxsw shows a proper value (either by implementing all
dpipe tables or changing how it is calculated) it should not be
returning that attribute. As it stands you are giving a user invalid data.

> 
>>
>>
>>
>> How does a user learn the granularity of a resource:
>>
>> $ devlink resource set pci/0000:03:00.0 path /kvd/hash_double size 50000
>> Error: mlxsw_spectrum: resource set with wrong granularity.
>>
>> Try again with 51000 and then 52000 and ... Why not export the
>> granularity read-only? I don't see it in the proposed UAPI.
>>
> 
> I would like more adding the granularity size to the extack string
> instead of adding this to UAPI. The user will try to update once
> and will get the required granularity in the error message.

A user should not have to run a command to get an error message to know
essential data to running a command with the right value. Further, do
not assume 'user' is a person or the devlink command.

Since granularity is essential to running a valid command, it should be
an attribute for each resource.

> 
>>
>> And then on the reload:
>>
>> $ devlink reload pci/0000:03:00.0
>> Error: devlink: resources size validation failed.
>>
>> Since the reload is not doing any resource sizing that error message is
>> confusing. Maybe something like "Sum of the resource components exceeds
>> total size."
>>
> 
> No problem, sounds better.
> 
>>
>> Finally, I still contend a 1-line description of each of the resources
>> goes a long way to improving the user friendliness of this set.
>>
> 
> Strongly against it.
>