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

Ian Kumlien
2020-12-15T13:10:41Z

On Tue, Dec 15, 2020 at 1:40 AM Bjorn Helgaas <helgaas@kernel.org> wrote:
>
> 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.

It was nice to find it for easy disabling :)

> > 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.

ASUS Pro WS X570-ACE with AMD Ryzen 9 3900X

> 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.

Same chipset it seems

I'm running bios version:
Version: 2206
Release Date: 08/13/2020

ANd latest is:
Version 3003
2020/12/07

Will test upgrading that as well, but it could be that they report the
incorrect latency of the switch - I don't know how many things AGESA
changes but... It's been updated twice since my upgrade.

> Bjorn