netdev - Re: mlxsw and rtnl lock

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Date:   Wed, 30 Aug 2017 00:18:52 +0300
From:   Arkadi Sharshevsky <arkadis@...lanox.com>
To:     David Ahern <dsahern@...il.com>, Ido Schimmel <idosch@...sch.org>
Cc:     Jiri Pirko <jiri@...nulli.us>,
        "netdev@...r.kernel.org" <netdev@...r.kernel.org>,
        mlxsw@...lanox.com
Subject: Re: mlxsw and rtnl lock



On 08/29/2017 11:04 PM, David Ahern wrote:
> On 8/29/17 12:10 AM, Arkadi Sharshevsky wrote:
>>
>>
>> On 08/28/2017 09:00 PM, David Ahern wrote:
>>> On 8/26/17 11:04 AM, Ido Schimmel wrote:
>>>> Regarding the silent abort, that's intentional. You can look at the same
>>>> code in v4.9 - when the chain was still blocking - and you'll see that
>>>> we didn't propagate the error even then. This was discussed in the past
>>>> and the conclusion was that user doesn't expect to operation to fail. If
>>>> hardware resources are exceeded, we let the kernel take care of the
>>>> forwarding instead.
>>>>
>>>
>>> In addition to Roopa's comments... The silent abort is not a good user
>>> experience. Right now it's add a network address or route, cross fingers
>>> and hope it does not overflow some limit (nexthop, ecmp, neighbor,
>>> prefix, etc) that triggers the offload abort.
>>>
>>> The mlxsw driver queries for some limits (e.g., max rifs) but I don't
>>> see any query related to current usage, and there is no API to pass any
>>> of that data to user space so user space has no programmatic way to
>>> handle this. I realize you are aware of this limitation. The point is to
>>> emphasize the need to resolve this.
>>>
>>
>> We actually thought about providing he user some tools to understand
>> the ASIC's limitations by introducing the 'resource' object to devlink.
>>
>> By linking dpipe tables to resources the user can understand which
>> hardware processes share a common resource, furthermore this resources
>> usage could be observed. By this more visibility can be obtained.
>>
>> Its not a remedy for the silent abort, but, maybe a notification
>> can be sent from devlink in case of abort that some resources is
>> full.
>>
>> This proposition was sent as RFC several weeks ago.
>>
> 
> Do you have patches (kernel and devlink) for the proposal?
> 

No, only the design RFC which describe the UAPI, devlink
commands and the devlink/driver interactions.

I wanted to receive some feedback before the coding.