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

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Message-ID: <e6f8e86d-62ee-4fc8-a92d-3fc6e963433c@gmail.com>
Date: Tue, 5 Nov 2024 22:28:17 +0100
From: Heiner Kallweit <hkallweit1@...il.com>
To: Felix Braun <f.braun@...ix.de>, nic_swsd@...ltek.com
Cc: netdev@...r.kernel.org
Subject: Re: r8169: regression in connection speed with kernels 6.2+
 (interrupt coalescing)

On 05.11.2024 20:57, Felix Braun wrote:
> 
> On 04.11.2024 14:57 +0100 Heiner Kallweit wrote:
>> On 04.11.2024 13:47, Felix Braun wrote:
>>> 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.)
>>>
>>
>> This test case involves several layers. To rule out conflicts on higher
> levels:  
>> Can you test with iperf to another machine in the same local network?
> 
> Measuring the performance with iperf3 I still see a difference in throughput by
> a factor of 3:
> 
> WITH napi_defer_hard_irqs=0
> ===========================
> [  5] local 2001:a61:11c6:9501:982a:b19f:94fc:71d1 port 41716 connected to
> 2001:a61:11c6:9501:97a8:b80a:4317:435e port 5201
> [ ID] Interval           Transfer     Bitrate         Retr  Cwnd
> [  5]   0.00-1.00   sec   112 MBytes   941 Mbits/sec    0    315 KBytes
> [  5]   1.00-2.00   sec   110 MBytes   927 Mbits/sec    0    340 KBytes
> [  5]   2.00-3.00   sec   111 MBytes   930 Mbits/sec    0    372 KBytes
> [  5]   3.00-4.00   sec   111 MBytes   930 Mbits/sec    0    372 KBytes
> [  5]   4.00-5.00   sec   110 MBytes   926 Mbits/sec    0    372 KBytes
> [  5]   5.00-6.00   sec   111 MBytes   929 Mbits/sec    0    372 KBytes
> [  5]   6.00-7.00   sec   110 MBytes   924 Mbits/sec    0    372 KBytes
> [  5]   7.00-8.00   sec   111 MBytes   932 Mbits/sec    0    372 KBytes
> [  5]   8.00-9.00   sec   110 MBytes   924 Mbits/sec    0    372 KBytes
> [  5]   9.00-10.00  sec   111 MBytes   928 Mbits/sec    0    372 KBytes
> - - - - - - - - - - - - - - - - - - - - - - - - -
> [ ID] Interval           Transfer     Bitrate         Retr
> [  5]   0.00-10.00  sec  1.08 GBytes   929 Mbits/sec    0             sender
> [  5]   0.00-10.00  sec  1.08 GBytes   928 Mbits/sec                  receiver
> 
> WITH napi_defer_hard_irqs=1
> ===========================
> Connecting to host leporello, port 5201
> [  5] local 2001:a61:11c6:9501:982a:b19f:94fc:71d1 port 42338 connected to
> 2001:a61:11c6:9501:97a8:b80a:4317:435e port 5201
> [ ID] Interval           Transfer     Bitrate         Retr  Cwnd
> [  5]   0.00-1.00   sec  37.0 MBytes   310 Mbits/sec    0    806 KBytes
> [  5]   1.00-2.00   sec  35.0 MBytes   294 Mbits/sec    0    806 KBytes
> [  5]   2.00-3.00   sec  35.1 MBytes   294 Mbits/sec    0    806 KBytes
> [  5]   3.00-4.00   sec  35.0 MBytes   294 Mbits/sec    0    806 KBytes
> [  5]   4.00-5.00   sec  35.2 MBytes   296 Mbits/sec    0    806 KBytes
> [  5]   5.00-6.00   sec  35.0 MBytes   294 Mbits/sec    0    806 KBytes
> [  5]   6.00-7.00   sec  34.9 MBytes   293 Mbits/sec    0    806 KBytes
> [  5]   7.00-8.00   sec  34.9 MBytes   293 Mbits/sec    0    806 KBytes
> [  5]   8.00-9.00   sec  35.0 MBytes   294 Mbits/sec    0    806 KBytes
> [  5]   9.00-10.00  sec  35.2 MBytes   295 Mbits/sec    0    806 KBytes
> - - - - - - - - - - - - - - - - - - - - - - - - -
> [ ID] Interval           Transfer     Bitrate         Retr
> [  5]   0.00-10.00  sec   352 MBytes   296 Mbits/sec    0             sender
> [  5]   0.00-10.02  sec   349 MBytes   292 Mbits/sec                  receiver
> 
Could you please test also in the other direction (with option -R)?

> 
>> Would be worth a try to see how system behaves with ASPM enabled in the
> kernel.  
>> Even though BIOS denies ASPM access for the kernel:  
>> "can't disable ASPM; OS doesn't have ASPM control"
> 
> I noticed that I disabled ASPM in the BIOS. So far I've not been able to find a
> BIOS setting that makes that warning go away.
> 
> If you think, that the current settings are the best default values for most
> users, I'd defer your better knowledge of the hardware. At least I'm happy
> because I can get my performance back by disabling IRQ coalescing on a vanilla
> kernel.
> 
On a small N100-based system I can't reproduce the issue with the same chip version.
Even 2.5Gbps works with full line speed on this system.
OK, your CPU is even weaker, but this still shouldn't cause such a performance drop.
More the opposite, as software interrupt coalescing reduces the CPU load.
However there's nothing special with your system, according to the dmesg log.

> Regards
> Felix

Heiner