Re: [RFC] net: stmmac: keep RXC running in LPI mode to avoid systemoverload

[Giuseppe CAVALLARO]

Hello Romain
On 10/13/2013 10:02 PM, Romain Baeriswyl wrote:
> Hello Guiseppe,
>
> Thanks for your answer. Please find below some details and answers.
>
> > > In order to avoid system overload, the clock RXC from the Phy
> > > should not be
> > > stopped when in LPI mode.
> > >
> > > With the RTL8211E PHY which support EEE mode and with Apple Airport
> > > Extreme that
> > > supports it also, the kernel get frozen as soon as some Ethernet
> > > transfers are
> >
> >
> > hmm, I have a board with this transceiver so I could do some tests
> > this could take a while, unfortunately.
> >
> > > on-going. System seems to be overloaded with too many interrupts.
> > > The 'top'
> > > command reports often around ~80% irq.
> >
> > do you mean lpi mac interrupts?
>
> By disabling the LPI mode with ethtool --set-eee eth0 eee off, the
> interrupt overload remains. Both counters irq_rx_path_in_lpi_mode_n and
> irq_rx_path_exit_lpi_mode_n continue to run meaning the PHY continue
> to put the RX path in LPI mode.
>
> Only way I found to get ride of the overload is to keep the RX_CLK running
> in LPI mode. In this configuration, the RX link still continue to go in
> LPI mode and the two above counters continue to run.
>
> > > By letting the RXC clock running even in LPI mode as proposed
> > > below, the issue
> > > seems solved. Is it the right way to proceed?
> >
> > For EEE capability, RX_CLK may be halted for this reason i used it as
> > default in the stmmac and never seen your issue.
> >
> > > What is the power impact to not stop RXC in LPI mode?
> >
> > I can point you to "22.2.2.8a Receive direction LPI transition"
> > in IEEE802-3az... where is it reported that the PHY  halt the RX_CLK
> > in LPI mode.
>
> Actually the PHY "may" stop RX_CLK.

Another option it could be add a new parameter to enable/disable it.
We can decide a parameter for the stmmac or something for ethtool.

> > May I suspect some issues on your HW? or disable it with ethtool
>
> Yes, it could be HW issue. It would be very useful if you could reproduce
> the setup using a SoC with "DesignWare Cores Ethernet MAC" core,
> the RTL8211E PHY and an Apple Airport Extreme. The issue could well be between
> the controller and the PHY.
>
> Which Ethernet switch or router did you use to test the EEE mode?

when I tested EEE I connected with P2P two STi boards.
You can test it too.

> I may try these equipments as well.

peppe

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