linux-kernel - Re: [RFC] [PATCH net-next v4] [PATCH 2/2] r8169: Implement dynamic ASPM mechanism

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Date:   Mon, 6 Sep 2021 17:34:40 +0200
From:   Heiner Kallweit <hkallweit1@...il.com>
To:     Kai-Heng Feng <kai.heng.feng@...onical.com>
Cc:     nic_swsd <nic_swsd@...ltek.com>,
        Bjorn Helgaas <bhelgaas@...gle.com>,
        David Miller <davem@...emloft.net>,
        Jakub Kicinski <kuba@...nel.org>,
        Anthony Wong <anthony.wong@...onical.com>,
        Linux Netdev List <netdev@...r.kernel.org>,
        Linux PCI <linux-pci@...r.kernel.org>,
        LKML <linux-kernel@...r.kernel.org>,
        Bjorn Helgaas <helgaas@...nel.org>
Subject: Re: [RFC] [PATCH net-next v4] [PATCH 2/2] r8169: Implement dynamic
 ASPM mechanism

On 06.09.2021 17:10, Kai-Heng Feng wrote:
> On Sat, Sep 4, 2021 at 4:00 AM Heiner Kallweit <hkallweit1@...il.com> wrote:
>>
>> On 03.09.2021 17:56, Kai-Heng Feng wrote:
>>> On Tue, Aug 31, 2021 at 2:09 AM Bjorn Helgaas <helgaas@...nel.org> wrote:
>>>>
>>>> On Sat, Aug 28, 2021 at 01:14:52AM +0800, Kai-Heng Feng wrote:
>>>>> r8169 NICs on some platforms have abysmal speed when ASPM is enabled.
>>>>> Same issue can be observed with older vendor drivers.
>>>>>
>>>>> The issue is however solved by the latest vendor driver. There's a new
>>>>> mechanism, which disables r8169's internal ASPM when the NIC traffic has
>>>>> more than 10 packets, and vice versa. The possible reason for this is
>>>>> likely because the buffer on the chip is too small for its ASPM exit
>>>>> latency.
>>>>
>>>> This sounds like good speculation, but of course, it would be better
>>>> to have the supporting data.
>>>>
>>>> You say above that this problem affects r8169 on "some platforms."  I
>>>> infer that ASPM works fine on other platforms.  It would be extremely
>>>> interesting to have some data on both classes, e.g., "lspci -vv"
>>>> output for the entire system.
>>>
>>> lspci data collected from working and non-working system can be found here:
>>> https://bugzilla.kernel.org/show_bug.cgi?id=214307
>>>
>>>>
>>>> If r8169 ASPM works well on some systems, we *should* be able to make
>>>> it work well on *all* systems, because the device can't tell what
>>>> system it's in.  All the device can see are the latencies for entry
>>>> and exit for link states.
>>>
>>> That's definitely better if we can make r8169 ASPM work for all platforms.
>>>
>>>>
>>>> IIUC this patch makes the driver wake up every 1000ms.  If the NIC has
>>>> sent or received more than 10 packets in the last 1000ms, it disables
>>>> ASPM; otherwise it enables ASPM.
>>>
>>> Yes, that's correct.
>>>
>>>>
>>>> I asked these same questions earlier, but nothing changed, so I won't
>>>> raise them again if you don't think they're pertinent.  Some patch
>>>> splitting comments below.
>>>
>>> Sorry about that. The lspci data is attached.
>>>
>>
>> Thanks for the additional details. I see that both systems have the L1
>> sub-states active. Do you also face the issue if L1 is enabled but
>> L1.2 and L1.2 are not? Setting the ASPM policy from powersupersave
>> to powersave should be sufficient to disable them.
>> I have a test system Asus PRIME H310I-PLUS, BIOS 2603 10/21/2019 with
>> the same RTL8168h chip version. With L1 active and sub-states inactive
>> everything is fine. With the sub-states activated I get few missed RX
>> errors when running iperf3.
> 
> Once L1.1 and L1.2 are disabled the TX speed can reach 710Mbps and RX
> can reach 941 Mbps. So yes it seems to be the same issue.

I reach 940-950Mbps in both directions, but this seems to be unrelated
to what we discuss here.

> With dynamic ASPM, TX can reach 750 Mbps while ASPM L1.1 and L1.2 are enabled.
> 
>> One difference between your good and bad logs is the following.
>> (My test system shows the same LTR value like your bad system.)
>>
>> Bad:
>>         Capabilities: [170 v1] Latency Tolerance Reporting
>>                 Max snoop latency: 3145728ns
>>                 Max no snoop latency: 3145728ns
>>
>> Good:
>>         Capabilities: [170 v1] Latency Tolerance Reporting
>>                 Max snoop latency: 1048576ns
>>                 Max no snoop latency: 1048576ns
>>
>> I have to admit that I'm not familiar with LTR and don't know whether
>> this difference could contribute to the differing behavior.
> 
> I am also unsure what role LTR plays here, so I tried to change the
> LTR value to 1048576ns and yield the same result, the TX and RX remain
> very slow.
> 
> Kai-Heng
>