netdev - Re: [PATCH net] r8169: switch off ASPM by default and add sysfs attribute to control ASPM

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Message-ID: <20190409182039.GB256045@google.com>
Date:   Tue, 9 Apr 2019 13:20:39 -0500
From:   Bjorn Helgaas <helgaas@...nel.org>
To:     Heiner Kallweit <hkallweit1@...il.com>
Cc:     Frederick Lawler <fred@...dlawl.com>,
        Florian Fainelli <f.fainelli@...il.com>,
        David Miller <davem@...emloft.net>,
        Realtek linux nic maintainers <nic_swsd@...ltek.com>,
        "netdev@...r.kernel.org" <netdev@...r.kernel.org>,
        "linux-pci@...r.kernel.org" <linux-pci@...r.kernel.org>,
        Rajat Jain <rajatja@...gle.com>
Subject: Re: [PATCH net] r8169: switch off ASPM by default and add sysfs
 attribute to control ASPM

On Tue, Apr 09, 2019 at 07:32:15PM +0200, Heiner Kallweit wrote:
> On 05.04.2019 21:28, Heiner Kallweit wrote:
> > On 05.04.2019 21:10, Bjorn Helgaas wrote:
> >> On Wed, Apr 03, 2019 at 07:45:29PM +0200, Heiner Kallweit wrote:
> >>> On 03.04.2019 15:14, Bjorn Helgaas wrote:
> >>>> On Wed, Apr 03, 2019 at 07:53:40AM +0200, Heiner Kallweit wrote:
> >>>>> On 02.04.2019 23:57, Bjorn Helgaas wrote:
> >>>>>> On Tue, Apr 02, 2019 at 10:41:20PM +0200, Heiner Kallweit wrote:
> >>>>>>> On 02.04.2019 22:16, Florian Fainelli wrote:
> >>>>>>>> On 4/2/19 12:55 PM, Heiner Kallweit wrote:
> >>>>>>>>> There are numerous reports about different problems caused by
> >>>>>>>>> ASPM incompatibilities between certain network chip versions
> >>>>>>>>> and board chipsets. On the other hand on (especially mobile)
> >>>>>>>>> systems where ASPM works properly it can significantly
> >>>>>>>>> contribute to power-saving and increased battery runtime.
> >>>>>>>>> One problem so far to make ASPM configurable was to find an
> >>>>>>>>> acceptable way of configuration (e.g. module parameters are
> >>>>>>>>> discouraged for that purpose).
> >>
> >>>>>>>>> +Certain combinations of network chip versions and board
> >>>>>>>>> +chipsets result in increased packet latency, PCIe errors, or
> >>>>>>>>> +significantly reduced network performance. Therefore ASPM is
> >>>>>>>>> +off by default. On the other hand ASPM can significantly
> >>>>>>>>> +contribute to power-saving and thus increased battery runtime
> >>>>>>>>> +on notebooks.
> >>
> >>>> That said, I think Frederick has already started working on a plan
> >>>> for the PCI core to expose sysfs files to manage ASPM.  This is
> >>>> similar to the link_state files enabled by CONFIG_PCIEASPM_DEBUG,
> >>>> but it will be always enabled and probably structured slightly
> >>>> differently.  The idea is that this would be generic and would not
> >>>> require any driver support.
> >>
> >>> Frederick, is there anything you could share already? Or any timeline?
> >>> Based on Bjorns info what seems to be best to me:
> >>> 1. Disable ASPM for r8169 on stable (back to 4.19).
> >>> 2. Once the generic ASPM sysfs attributes are available, reenable ASPM
> >>>    for r8169 in net-next.
> >>
> >> This is out of my wheelhouse, but even with a generic sysfs knob, it
> >> doesn't sound like a good idea to me to enable ASPM by default for
> >> r8169 if we think it's unreliable on any significant fraction of
> >> machines.
> >>
> > I was a little bit imprecise. With the second statement I wanted to say:
> > Keep ASPM disabled per default, but make it possible that setting the
> > new sysfs attribute enables ASPM. After digging deeper in the ASPM core
> > code it seems however that we don't even have to touch the driver later.
> 
> ASPM has been disabled again for r8169: b75bb8a5b755 ("r8169: disable ASPM
> again"). So, coming back to controlling ASPM via sysfs:
> My first thought would be to extend pci_disable_link_state with support
> for disabling L1.1/L1.2, and then basically expose pci_disable_link_state
> via sysfs (attribute reading being handled with a direct read from
> pcie_link_state->aspm_disable).
> 
> Is this what you were planning or do you have some other approach in mind?

I can't remember the details of what Frederick and I talked about, but
I think that's the general approach.

Bjorn