netdev - Re: "r8169: Reinstate ASPM Support" causes increased packet latency on Asus H87M-E motherboard

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Message-ID: <83e1f49a-ff41-7f3b-b758-244ce95499c6@gmail.com>
Date:   Wed, 27 Mar 2019 19:46:45 +0100
From:   Heiner Kallweit <hkallweit1@...il.com>
To:     Mike Crowe <mac@...owe.com>, netdev@...r.kernel.org,
        Kai-Heng Feng <kai.heng.feng@...onical.com>,
        David Chang <dchang@...e.com>
Cc:     Chunhao Lin <hau@...ltek.com>
Subject: Re: "r8169: Reinstate ASPM Support" causes increased packet latency
 on Asus H87M-E motherboard

On 27.03.2019 16:20, Mike Crowe wrote:
> On Wednesday 27 March 2019 at 15:05:46 +0000, Mike Crowe wrote:
>> After upgrading the kernel to v4.19 we started seeing increased packet
>> latency on two machines with ASUS H87M-E motherboards with on-board Realtek
>> Gigabit Ethernet. This didn't happen with v4.18. (More details, including
>> kernel log and lspci output at
>> https://bugs.debian.org/cgi-bin/bugreport.cgi?bug=925496 )
>>
>> Bisecting revealed that commit
>>
>>  a99790bf5c7f3d68d8b01e015d3212a98ee7bd57  r8169: Reinstate ASPM Support
>>
>> provoked this change in behaviour.
>>
>> If I patch v4.9.31's drivers/net/ethernet/realtek/r8169.c
>> rtl_hw_aspm_clkreq_enable function to never enable the clocks (which,
>> AFAICT, is equivalent to reverting the aforementioned commit) then packet
>> latency is normal.
>>
>> The increased packet latency can also be resolved by:
>>
>> 1. Running 'ethtool -C eth0 rx-usecs 0 rx-frames 1'
>>
>> 2. Disabling "EPU Power Saving Mode" in the BIOS (on the Ai Tweaker page.)
>>    This option is enabled when the "ASUS Optimal" setting is selected on
>>    the BIOS front page.
>>
>> but neither of these solutions are ideal because they require the user to
>> realise that there's a problem and discover these solutions.
>>
>> Is there a way to fix the code to work correctly with this motherboard even
>> with "EPU Power Saving Mode" enabled?
> 
> Unfortunately, my searching prior to sending that email did not reveal that
> this problem has been reported before[1]. Apologies for the noise.
> 
> Mike.
> 
> [1] https://lore.kernel.org/netdev/CAMLO_R7Q6QCr7KX5goOvJ_BzDLU_tnw3UkMKzwDmL4C2BHubVA@mail.gmail.com/
> 
Thanks for the report. Actually the ASPM-related issue seems to occur in
different flavors, but it affects only a certain number of network chip /
board combinations (even though it's not known which combinations).
And it's not clear who's to blame, board/BIOS or network chip. Most likely
both. Unfortunately disabling ASPM would result in notebook users
complaining, because ASPM provides a significant power saving.

But interesting is that the mentioned coalesce setting fixes the issue for
you. I'll check with other affected users whether it's the same for them.

Heiner