netdev - Re: [PATCH net] ionic: centralize queue reset code

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Date:   Tue, 7 Jul 2020 11:04:28 -0700
From:   Shannon Nelson <snelson@...sando.io>
To:     Jakub Kicinski <kuba@...nel.org>
Cc:     netdev@...r.kernel.org, davem@...emloft.net
Subject: Re: [PATCH net] ionic: centralize queue reset code

On 7/7/20 9:46 AM, Jakub Kicinski wrote:
> On Tue, 7 Jul 2020 09:10:38 -0700 Shannon Nelson wrote:
>> On 7/6/20 10:33 AM, Jakub Kicinski wrote:
>>> On Thu,  2 Jul 2020 16:39:17 -0700 Shannon Nelson wrote:
>>>> The queue reset pattern is used in a couple different places,
>>>> only slightly different from each other, and could cause
>>>> issues if one gets changed and the other didn't.  This puts
>>>> them together so that only one version is needed, yet each
>>>> can have slighty different effects by passing in a pointer
>>>> to a work function to do whatever configuration twiddling is
>>>> needed in the middle of the reset.
>>>>
>>>> Fixes: 4d03e00a2140 ("ionic: Add initial ethtool support")
>>>> Signed-off-by: Shannon Nelson <snelson@...sando.io>
>>> Is this fixing anything?
>> Yes, this fixes issues seen similar to what was fixed with b59eabd23ee5
>> ("ionic: tame the watchdog timer on reconfig") where under loops of
>> changing parameters we could occasionally bump into the netdev watchdog.
> User-visible bug should always be part of the commit message for a fix,
> please amend.

Sure, I'll follow up later today.

>
>>> I think the pattern of having a separate structure describing all the
>>> parameters and passing that into reconfig is a better path forward,
>>> because it's easier to take that forward in the correct direction of
>>> allocating new resources before old ones are freed. IOW not doing a
>>> full close/open.
>>>
>>> E.g. nfp_net_set_ring_size().
>> This has been suggested before and looks great when you know you've got
>> the resources for dual allocations.  In our case this code is also used
>> inside our device where memory is tight: we are much more likely to have
>> allocation issues if we try to allocate everything without first
>> releasing what we already have.
> Are you saying that inside the device the memory allocated for the
> rings is close to the amount of max free memory? I find that hard to
> believe.
>
I was a bit surprised as well, but there is a lot going on inside the 
device and it turns out there are one or two specific use cases where 
this is an issue.

sln