netdev - Re: [patch net-next 11/12] mlxsw: spectrum_dpipe: Add support for IPv4 host table dump

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Message-ID: <f5bd669b-6a0f-46e9-97b9-7abe73a228a5@gmail.com>
Date:   Mon, 28 Aug 2017 20:57:12 -0600
From:   David Ahern <dsahern@...il.com>
To:     Arkadi Sharshevsky <arkadis@...lanox.com>,
        Jiri Pirko <jiri@...nulli.us>, netdev@...r.kernel.org
Cc:     davem@...emloft.net, idosch@...lanox.com, mlxsw@...lanox.com,
        roopa <roopa@...ulusnetworks.com>,
        Shrijeet Mukherjee <shm@...ulusnetworks.com>
Subject: Re: [patch net-next 11/12] mlxsw: spectrum_dpipe: Add support for
 IPv4 host table dump

On 8/27/17 2:31 AM, Arkadi Sharshevsky wrote:
>> Also, this dpipe capability seems to be just dumping data structures
>> maintained by the driver. ie., you can compare the mlxsw view of
>> networking state to IPv4 and IPv6 level tables. Any plans to offer a
>> command that reads data from the h/w and passes that back to the user?
>> i.e, a command to compare kernel tables to h/w state?
>>
> 
> So this infra should provide several things-
> 
> 1) Reveal the interactions between various hardware tables
> 2) Counters for this tables
> 3) Debugabillity
> 
> The first two can be achieved right now. Regarding debugabillity, which
> is a bit vague, the current assumption is that the drivers internal data
> structures are synced with hardware (which is no always true), and maybe
> are not synced with the kernel, so this can be achieved right now by
> dumping the internal state of the driver. Furthermore, the counters are
> dumped from the hardware and give the user additional indication.
> 
> I completely agree that the hardware should be dumped in order to
> validate the internal data structures are really synced with HW. This
> could be usable for observing data corruptions inside the ASIC and
> various complex bugs.
> 
> In order to address that I though about maybe add a flag called
> "validate_hw" so that during the dump the driver<-->hw state could be
> validated.
> 
> What do you think about it?

It is not just a matter of dumping hardware state. The data returned by
dump needs to be consistent across platforms and vendors.

If the intent is validating hardware state matches kernel state (ie.,
h/w forwarding matches s/w forwarding), then the hardware state should
be dumped by the driver in a form that parallels kernel state. e.g.,
dump h/w routes, neighbor entries, fdb's in a form and granularity
similar to what is done for kernel tables.

With the recent dpipe changes that allows kernel to driver cache and
kernel to h/w state comparisons.