linux-kernel - Re: [RFC] net: stmmac: keep RXC running in LPI mode to avoid system overload

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Message-ID: <525EF70C.9090708@st.com>
Date:	Wed, 16 Oct 2013 22:29:00 +0200
From:	Giuseppe CAVALLARO <peppe.cavallaro@...com>
To:	Romain Baeriswyl <Romain.Baeriswyl@...lis.com>
Cc:	"David S. Miller" <davem@...emloft.net>, <netdev@...r.kernel.org>,
	<linux-kernel@...r.kernel.org>,
	Christian Ruppert <chrisr@...lis.com>
Subject: Re: [RFC] net: stmmac: keep RXC running in LPI mode to avoid system
 overload

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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