Re: [PATCH 1/3] PCI/ASPM: Use the path max in L1 ASPM latency check

Bjorn Helgaas
2020-12-15T00:40:56Z

On Mon, Dec 14, 2020 at 11:56:31PM +0100, Ian Kumlien wrote:
> On Mon, Dec 14, 2020 at 8:19 PM Bjorn Helgaas <helgaas@kernel.org> wrote:

> > If you're interested, you could probably unload the Realtek drivers,
> > remove the devices, and set the PCI_EXP_LNKCTL_LD (Link Disable) bit
> > in 02:04.0, e.g.,
> >
> > # RT=/sys/devices/pci0000:00/0000:00:01.2/0000:01:00.0/0000:02:04.0
> > # echo 1 > $RT/0000:04:00.0/remove
> > # echo 1 > $RT/0000:04:00.1/remove
> > # echo 1 > $RT/0000:04:00.2/remove
> > # echo 1 > $RT/0000:04:00.4/remove
> > # echo 1 > $RT/0000:04:00.7/remove
> > # setpci -s02:04.0 CAP_EXP+0x10.w=0x0010
> >
> > That should take 04:00.x out of the picture.
>
> Didn't actually change the behaviour, I'm suspecting an errata for AMD pcie...
>
> So did this, with unpatched kernel:
> [ ID] Interval Transfer Bitrate Retr Cwnd
> [ 5] 0.00-1.00 sec 4.56 MBytes 38.2 Mbits/sec 0 67.9 KBytes
> [ 5] 1.00-2.00 sec 4.47 MBytes 37.5 Mbits/sec 0 96.2 KBytes
> [ 5] 2.00-3.00 sec 4.85 MBytes 40.7 Mbits/sec 0 50.9 KBytes
> [ 5] 3.00-4.00 sec 4.23 MBytes 35.4 Mbits/sec 0 70.7 KBytes
> [ 5] 4.00-5.00 sec 4.23 MBytes 35.4 Mbits/sec 0 48.1 KBytes
> [ 5] 5.00-6.00 sec 4.23 MBytes 35.4 Mbits/sec 0 45.2 KBytes
> [ 5] 6.00-7.00 sec 4.23 MBytes 35.4 Mbits/sec 0 36.8 KBytes
> [ 5] 7.00-8.00 sec 3.98 MBytes 33.4 Mbits/sec 0 36.8 KBytes
> [ 5] 8.00-9.00 sec 4.23 MBytes 35.4 Mbits/sec 0 36.8 KBytes
> [ 5] 9.00-10.00 sec 4.23 MBytes 35.4 Mbits/sec 0 48.1 KBytes
> - - - - - - - - - - - - - - - - - - - - - - - - -
> [ ID] Interval Transfer Bitrate Retr
> [ 5] 0.00-10.00 sec 43.2 MBytes 36.2 Mbits/sec 0 sender
> [ 5] 0.00-10.00 sec 42.7 MBytes 35.8 Mbits/sec receiver
>
> and:
> echo 0 > /sys/devices/pci0000:00/0000:00:01.2/0000:01:00.0/link/l1_aspm

BTW, thanks a lot for testing out the "l1_aspm" sysfs file. I'm very
pleased that it seems to be working as intended.

> and:
> [ ID] Interval Transfer Bitrate Retr Cwnd
> [ 5] 0.00-1.00 sec 113 MBytes 951 Mbits/sec 153 772 KBytes
> [ 5] 1.00-2.00 sec 109 MBytes 912 Mbits/sec 276 550 KBytes
> [ 5] 2.00-3.00 sec 111 MBytes 933 Mbits/sec 123 625 KBytes
> [ 5] 3.00-4.00 sec 111 MBytes 933 Mbits/sec 31 687 KBytes
> [ 5] 4.00-5.00 sec 110 MBytes 923 Mbits/sec 0 679 KBytes
> [ 5] 5.00-6.00 sec 110 MBytes 923 Mbits/sec 136 577 KBytes
> [ 5] 6.00-7.00 sec 110 MBytes 923 Mbits/sec 214 645 KBytes
> [ 5] 7.00-8.00 sec 110 MBytes 923 Mbits/sec 32 628 KBytes
> [ 5] 8.00-9.00 sec 110 MBytes 923 Mbits/sec 81 537 KBytes
> [ 5] 9.00-10.00 sec 110 MBytes 923 Mbits/sec 10 577 KBytes
> - - - - - - - - - - - - - - - - - - - - - - - - -
> [ ID] Interval Transfer Bitrate Retr
> [ 5] 0.00-10.00 sec 1.08 GBytes 927 Mbits/sec 1056 sender
> [ 5] 0.00-10.00 sec 1.07 GBytes 923 Mbits/sec receiver
>
> But this only confirms that the fix i experience is a side effect.
>
> The original code is still wrong :)

What exactly is this machine? Brand, model, config? Maybe you could
add this and a dmesg log to the buzilla? It seems like other people
should be seeing the same problem, so I'm hoping to grub around on the
web to see if there are similar reports involving these devices.

https://bugzilla.kernel.org/show_bug.cgi?id=209725

Here's one that is superficially similar:
https://linux-hardware.org/index.php?probe=e5f24075e5&log=lspci_all
in that it has a RP -- switch -- I211 path. Interestingly, the switch
here advertises <64us L1 exit latency instead of the <32us latency
your switch advertises. Of course, I can't tell if it's exactly the
same switch.

Bjorn