netdev - Re: [PATCH net] r8169: disable default rx interrupt coalescing on RTL8168

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Message-ID: <dedcb597-2e78-26c1-028e-fbf02bb3c0c4@gmail.com>
Date:   Sat, 30 Mar 2019 19:41:34 +0100
From:   Heiner Kallweit <hkallweit1@...il.com>
To:     David Miller <davem@...emloft.net>
Cc:     nic_swsd@...ltek.com, netdev@...r.kernel.org, mac@...owe.com
Subject: Re: [PATCH net] r8169: disable default rx interrupt coalescing on
 RTL8168

On 30.03.2019 19:06, David Miller wrote:
> From: Heiner Kallweit <hkallweit1@...il.com>
> Date: Sat, 30 Mar 2019 17:13:24 +0100
> 
>> It was reported that re-introducing ASPM, in combination with RX
>> interrupt coalescing, results in significantly increased packet
>> latency, see [0]. Disabling ASPM or RX interrupt coalescing fixes
>> the issue. Therefore change the driver's default to disable RX
>> interrupt coalescing. Users still have the option to enable RX
>> coalescing via ethtool.
>>
>> [0] https://bugs.debian.org/cgi-bin/bugreport.cgi?bug=925496
>>
>> Fixes: a99790bf5c7f ("r8169: Reinstate ASPM Support")
>> Reported-by: Mike Crowe <mac@...owe.com>
>> Signed-off-by: Heiner Kallweit <hkallweit1@...il.com>
> 
> Applied and queued up for -stable.
> 
> Frankly, I think we were better off with ASPM disabled.  But I know
> a lot of people find that unacceptable.
> 
Yes, I can hear the notebook owners scream already, and complain about
reduced battery runtime. It would help to have an opt-in option for
ASPM. But a module parameter for it is discouraged, and I see no other
acceptable way to control ASPM on the chip side. I could misuse some
ethtool callback or add a new tunable. But controlling a PCI feature
through ethtool doesn't sound too nice. Maybe I could add a sysfs
attribute.

> This chip has some many quirks/warts when ASPM is enabled, look how
> long it took us to A) get ASPM enabled reasonably and B) discover
> this bug.
>