Hi, Keith

-----Original Message-----
From: Keith Busch [mailto:kbusch@kernel.org]
Sent: Tuesday, October 26, 2021 12:16 PM
To: Li Chen
Cc: Bjorn Helgaas; linux-pci@vger.kernel.org; Lorenzo Pieralisi; Rob Herring;
kw@linux.com; Bjorn Helgaas; linux-kernel@vger.kernel.org; Tom Joseph; Jens
Axboe; Christoph Hellwig; Sagi Grimberg; linux-nvme@lists.infradead.org
Subject: Re: [EXT] Re: nvme may get timeout from dd when using different non-
prefetch mmio outbound/ranges

On Tue, Oct 26, 2021 at 03:40:54AM +0000, Li Chen wrote:

quoted

My nvme is " 05:00.0 Non-Volatile memory controller: Samsung Electronics Co

Ltd NVMe SSD Controller 980". From its datasheet,
https://urldefense.com/v3/__https://s3.ap-northeast-
2.amazonaws.com/global.semi.static/Samsung_NVMe_SSD_980_Data_Sheet_R
ev.1.1.pdf__;!!PeEy7nZLVv0!3MU3LdTWuzON9JMUkq29zwJM4d7g7wKtkiZszTu-
PVepWchI_uLHpQGgdR_LEZM$ , it says nothing about CMB/SQEs, so I'm not sure.
Is there other ways/tools(like nvme-cli) to query?

The driver will export a sysfs property for it if it is supported:

  # cat /sys/class/nvme/nvme0/cmb

If the file doesn't exist, then /dev/nvme0 doesn't have the capability.

# ls /sys/class/nvme/nvme0/
address            model              rescan_controller  subsysnqn
cntlid             numa_node          reset_controller   subsystem
dev                nvme0n1            serial             transport
device             power              sqsize             uevent
firmware_rev       queue_count        state

my nvme doesn't cmb.

quoted

quoted

quoted

I don't know how to interpret "ranges".  Can you supply the dmesg and
"lspci -vvs 0000:05:00.0" output both ways, e.g.,

  pci_bus 0000:00: root bus resource [mem 0x7f800000-0xefffffff window]
  pci_bus 0000:00: root bus resource [mem 0xfd000000-0xfe7fffff window]
  pci 0000:05:00.0: [vvvv:dddd] type 00 class 0x...
  pci 0000:05:00.0: reg 0x10: [mem 0x.....000-0x.....fff ...]

quoted

Question:
1.  Why dd can cause nvme timeout? Is there more debug ways?

That means the nvme controller didn't provide a response to a posted
command within the driver's latency tolerance.

FYI, with the help of pci bridger's vendor, they find something interesting:

"From catc log, I saw some memory read pkts sent from SSD card, but its memory
range is within the memory range of switch down port. So, switch down port will
replay UR pkt. It seems not normal." and "Why SSD card send out some memory
pkts which memory address is within switch down port's memory range. If so,
switch will response UR pkts". I also don't understand how can this happen?

I think we can safely assume you're not attempting peer-to-peer, so that
behavior as described shouldn't be happening. It sounds like the memory
windows may be incorrect. The dmesg may help to show if something appears
wrong.

Dmesg has been pasted in https://marc.info/?l=linux-pci&m=163522281024680&w=3

Yes, peer-to-peer cannot happen, nvme is my only ep:

# lspci -i /usr/share/misc/pci.ids
00:00.0 PCI bridge: Cadence Design Systems, Inc. Device 0100
01:00.0 PCI bridge: Pericom Semiconductor Device c016 (rev 07)
02:02.0 PCI bridge: Pericom Semiconductor Device c016 (rev 06)
02:04.0 PCI bridge: Pericom Semiconductor Device c016 (rev 06)
02:06.0 PCI bridge: Pericom Semiconductor Device c016 (rev 06)
05:00.0 Non-Volatile memory controller: Samsung Electronics Co Ltd NVMe SSD Controller 980

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