RE: [EXT] Re: nvme may get timeout from dd when using different non-prefetch mmio outbound/ranges

[Li Chen]

Hi, Keith

> -----Original Message-----
> From: Keith Busch [mailto:kbusch@xxxxxxxxxx]
> Sent: Tuesday, October 26, 2021 12:16 PM
> To: Li Chen
> Cc: Bjorn Helgaas; linux-pci@xxxxxxxxxxxxxxx; Lorenzo Pieralisi; Rob Herring;
> kw@xxxxxxxxx; Bjorn Helgaas; linux-kernel@xxxxxxxxxxxxxxx; Tom Joseph; Jens
> Axboe; Christoph Hellwig; Sagi Grimberg; linux-nvme@xxxxxxxxxxxxxxxxxxx
> 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:
> > 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.


> > > > 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 ...]
> > > >
> > > > > 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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