netdev - Re: [net-next,v2] [PATCH net-next v2] net: wwan: t7xx: Change PM_AUTOSUSPEND

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Message-ID: <7e5e2bda-e80d-46ec-816a-613c5808222e@gmail.com>
Date: Tue, 19 Nov 2024 03:01:47 +0200
From: Sergey Ryazanov <ryazanov.s.a@...il.com>
To: Jakub Kicinski <kuba@...nel.org>
Cc: wojackbb@...il.com, netdev@...r.kernel.org,
 chandrashekar.devegowda@...el.com, chiranjeevi.rapolu@...ux.intel.com,
 haijun.liu@...iatek.com, m.chetan.kumar@...ux.intel.com,
 ricardo.martinez@...ux.intel.com, loic.poulain@...aro.org,
 johannes@...solutions.net, davem@...emloft.net, edumazet@...gle.com,
 pabeni@...hat.com, linux-arm-kernel@...ts.infradead.org,
 angelogioacchino.delregno@...labora.com, linux-mediatek@...ts.infradead.org,
 matthias.bgg@...il.com
Subject: Re: [net-next,v2] [PATCH net-next v2] net: wwan: t7xx: Change
 PM_AUTOSUSPEND_MS to 5000

On 16.11.2024 01:21, Jakub Kicinski wrote:
> On Thu, 14 Nov 2024 20:54:20 +0200 Sergey Ryazanov wrote:
>>> We tested Fibocom FM350 and our products using the t7xx and they all
>>> benefited from this.
>>
>> Possible negative outcomes for data transmission still need
>> clarification. Let me repeat it here.
>>
>> On 06.11.2024 13:10, 吳逼逼 wrote:
>>> Receiving or sending data will cause PCIE to change D3 Cold to D0 state.
>>
>> Am I understand it correctly that receiving IP packets on downlink will
>> cause PCIe link re-activation?
>>
>>
>> I am concerned about a TCP connection that can be idle for a long period
>> of time. For example, an established SSH connection can stay idle for
>> minutes. If I connected to a server and execute something like this:
>>
>> user@...t$ sleep 20 && echo "Done"
>>
>> Will I eventually see the "Done" message or will the autosuspended modem
>> effectively block any incoming traffic? And how long does it take for
>> the modem to wake up and deliver a downlink packet to the host? Have you
>> measured StDev change?
> 
> He's decreasing the sleep timer from 20 to 5 sec, both of which
> are very high for networking, anyway. You appear to be questioning
> autosuspend itself but it seems to have been added 2 years ago already.
> 
> What am I missing?

Some possible funny side-effect of sleeping with this chipset. Like 
loosing network connection and dropping TCP sessions. I hope that 20 
seconds was putted on purpose.

Suddenly, I don't have this modem at hand and want to be sure that we 
are not going to receive a stream of bug reports.

--
Sergey