Re: [dpdk-dev] [EXT] Re: [PATCH 2/2] net/qede: restore Tx queue setup

[Rasesh Mody <rmody@marvell.com>]

>From: Ferruh Yigit <ferruh.yigit@intel.com>
>Sent: Thursday, May 14, 2020 7:33 AM
>
>On 5/6/2020 3:43 AM, Rasesh Mody wrote:
>> Hi,
>>
>>> From: Thomas Monjalon <thomas@monjalon.net>
>>> Sent: Tuesday, May 05, 2020 2:15 AM
>>>
>>> 05/05/2020 10:59, Ferruh Yigit:
>>>> On 5/5/2020 7:44 AM, Jerin Jacob wrote:
>>>>> On Tue, May 5, 2020 at 8:39 AM Rasesh Mody <rmody@marvell.com>
>>> wrote:
>>>>>>
>>>>>> Some applications do not explicitly restore Tx queues setup during
>>>>>> port re-configuration. This patch adds changes to check for
>>>>>> released Tx queues and restore the setup if application doesn't
>>>>>> explicitly does that.
>>>>>
>>>>> +ethdev maintainers.
>>>>>
>>>>> I think, Ideally, the fix should be in common code if we need to
>>>>> support such applications.
>>>>
>>>> Is this a case application re-configures to increase the number of
>>>> queues but doesn't setup new queues?
>>>> If so this looks like application error and application should be
>>>> fixed instead of recover this in the ethdev.
>>>
>>> +1
>>>
>>
>> This is a case of KNI application performing device re-configuration to
>change MTU. The application explicitly calls Rx queue setup, however doesn't
>call Tx queue setup. When MTU for KNI interface is changed it runs into a
>segfault when trying to start Tx queues.
>
>Why it crash? Device re-configuration should not be changing the number of
>the queues, it is always 1. What is missing/wrong without the Tx queue setup?
>

QEDE PMD deallocates all fastpath resources unconditionally, including Tx queue, when re-configuring the device. When reallocating resources PMD relies on application to explicitly setup the Rx/Tx queue. 
Deallocation of all the resources is only required if the Rx/Tx queue configuration changes. So when KNI MTU change performs device re-configuration it exposes a bug, where there are no Tx queue resources setup. Then while starting the Tx queue in HW from PMD, application crashes.
I'll submit a PMD fix for device re-configuration.

>> Some other applications make use of rte_eth_dev_set_mtu() ethdev op,
>which looks to be cleaner approach.
>>
>
>+1. I don't know history if there is a specific reason this way
>+selected, but
>after release I think we can try this.

Sure.
Thanks!
-Rasesh