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

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Message-ID: <20190327152021.ybbpn6jcui4xg43j@mcrowe.com>
Date:   Wed, 27 Mar 2019 15:20:21 +0000
From:   Mike Crowe <mac@...owe.com>
To:     netdev@...r.kernel.org,
        Kai-Heng Feng <kai.heng.feng@...onical.com>,
        Heiner Kallweit <hkallweit1@...il.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 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/