netdev - RE: [EXT] Re: [net PATCH V2 1/4] octeontx2-pf: Update PFC configuration

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Date: Sat, 19 Aug 2023 10:10:00 +0000
From: Suman Ghosh <sumang@...vell.com>
To: Jakub Kicinski <kuba@...nel.org>
CC: Sunil Kovvuri Goutham <sgoutham@...vell.com>,
        Geethasowjanya Akula
	<gakula@...vell.com>,
        Subbaraya Sundeep Bhatta <sbhatta@...vell.com>,
        Hariprasad Kelam <hkelam@...vell.com>,
        "davem@...emloft.net"
	<davem@...emloft.net>,
        "edumazet@...gle.com" <edumazet@...gle.com>,
        "pabeni@...hat.com" <pabeni@...hat.com>,
        "netdev@...r.kernel.org"
	<netdev@...r.kernel.org>,
        "linux-kernel@...r.kernel.org"
	<linux-kernel@...r.kernel.org>,
        Linu Cherian <lcherian@...vell.com>,
        Jerin
 Jacob Kollanukkaran <jerinj@...vell.com>
Subject: RE: [EXT] Re: [net PATCH V2 1/4] octeontx2-pf: Update PFC
 configuration

>Thanks for replying a week late, always a good use of maintainers time
>to swap back all the context from random conversations!
[Suman] Sorry for being late this time Jakub. I will remove this patch from the patch set and will push a new version with the other three patches. I will analyze the issue in more detail and will produce a proper fix.
>
>On Fri, 18 Aug 2023 06:54:52 +0000 Suman Ghosh wrote:
>> >If there is any error in open() this will silently take the interface
>> >down. Can't you force a NAPI poll or some such, if the concern is a
>> >missed IRQ?
>> [Suman] I can check the return type of open() and report in case of
>> error. But even if we force NAPI poll we might not be able to control
>> the watchdog reset. If we have a running traffic and interface is up,
>> when we force NAPI poll, then the new packets will have updated
>> scheduler queue and we will still loose the completion interrupts of
>> the previous packets.
>
>Why does it matter that you lost an interrupt if the poll has happened.
>Can you describe the problem in more detail?
>
>> Do you see any issue if I handle the error situation during open()
>call?
>
>No, for years we have been rejecting code which does this.
>If the machine is under memory pressure allocating all the buffers for
>rings can easily fail and make the machine drop off the network.
>You either have to refuse to change this setting at runtime or implement
>prepare/commit reconfiguration model like other modern drivers, where
>allocations are done before the stop().