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

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Message-ID: <6835fde6-0863-49e8-90e8-be88e86ef346@gmail.com>
Date: Thu, 14 Nov 2024 20:54:20 +0200
From: Sergey Ryazanov <ryazanov.s.a@...il.com>
To: wojackbb@...il.com
Cc: 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, kuba@...nel.org, 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

Hello Jack,

On 14.11.2024 12:20, wojackbb@...il.com wrote:
> From: Jack Wu <wojackbb@...il.com>
> 
> Because optimizing the power consumption of t7XX,
> change auto suspend time to 5000.
> 
> The Tests uses a script to loop through the power_state
> of t7XX.
> (for example: /sys/bus/pci/devices/0000\:72\:00.0/power_state)
> 
> * If Auto suspend is 20 seconds,
>    test script show power_state have 0~5% of the time was in D3 state
>    when host don't have data packet transmission.
> 
> * Changed auto suspend time to 5 seconds,
>    test script show power_state have 50%~80% of the time was in D3 state
>    when host don't have data packet transmission.
> 
> 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?

> Signed-off-by: Jack Wu <wojackbb@...il.com>
> ---
> V2:
>   * supplementary commit information
> ---
> ---
>   drivers/net/wwan/t7xx/t7xx_pci.c | 2 +-
>   1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/drivers/net/wwan/t7xx/t7xx_pci.c b/drivers/net/wwan/t7xx/t7xx_pci.c
> index e556e5bd49ab..dcadd615a025 100644
> --- a/drivers/net/wwan/t7xx/t7xx_pci.c
> +++ b/drivers/net/wwan/t7xx/t7xx_pci.c
> @@ -48,7 +48,7 @@
>   #define T7XX_INIT_TIMEOUT		20
>   #define PM_SLEEP_DIS_TIMEOUT_MS		20
>   #define PM_ACK_TIMEOUT_MS		1500
> -#define PM_AUTOSUSPEND_MS		20000
> +#define PM_AUTOSUSPEND_MS		5000
>   #define PM_RESOURCE_POLL_TIMEOUT_US	10000
>   #define PM_RESOURCE_POLL_STEP_US	100
>