netdev - Re: r8169: regression in connection speed with kernels 6.2+ (interrupt coalescing)

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Message-ID: <a5bb19c7a363bef7e3a5f4abd69adb0c9fc666b5.camel@falix.de>
Date: Mon, 04 Nov 2024 13:47:56 +0100
From: Felix Braun <f.braun@...ix.de>
To: Heiner Kallweit <hkallweit1@...il.com>, nic_swsd@...ltek.com
Cc: netdev@...r.kernel.org
Subject: Re: r8169: regression in connection speed with kernels 6.2+
 (interrupt coalescing)

On 03.11.2024 23:21 +0100 Heiner Kallweit wrote:  
> Thanks for the report. 6.2 has been out for quite some time, and this is  
> the first such report. So I don't think there's a general problem.

I switched from 6.1 (stable) to 6.6 (stable) only recently and then I didn't notice the speed degradation for quite some time.

> Can you please provide a full dmesg log and elaborate on the type of traffic  
> and how you measure the speed? BTW: With 100MB/s you refer to 100MBit/s?

Nono, I mean 100MBytes/s ;-) My testcase is transferring a large file over SMB and looking at the transfer speed as reported by KDE. (I'm attaching a full dmsg of a boot of a 6.11.6 kernel with only irq_coalescing commented out otherwise as released.)

> Also interesting would be whether there are any errors or missed packets  
> in the ethtool -S <if> output.

No errors or misses in either patched or unpatched kernel.

> Instead of commenting out this line you can also adjust the values from userspace:  
> /sys/class/net/<if>/gro_flush_timeout  
> /sys/class/net/<if>/napi_defer_hard_irqs  
> Does increasing the gro_flush_timeout value change something for you?

That's cool. I've reverted to unchanged 6.11.6 and if I set napi_defer_hard_irqs to 0 I'm back to 100 MBytes/s. Playing with gro_flush_timeout while napi_defer_hard_irqs is set to 1 does not seem to have any effect on the trasfer speed. Default value is 20000. I have tried some values between 1000 and 200000.

> Somewhat strange is that lspci shows ASPM as disabled in LnkCtl, but  
> L1 sub-states are enabled in L1SubCtl1. Do you have any downstream kernel code  
> changes or any specific ASPM settings?

No. Other than patching the default value for interrupt coalescing, I'm running a vanilla kernel. Maybe it is because I didn't enable ASPM in the kernel configuration?

Thanks for taking this up.

Regards  
Felix

View attachment "dmsg.txt" of type "text/plain" (56167 bytes)