From: Dan Williams <email@example.com>
To: Jonathan Cameron <Jonathan.Cameron@huawei.com>
Cc: firstname.lastname@example.org, Linux PCI <email@example.com>,
Ben Widawsky <firstname.lastname@example.org>,
Bjorn Helgaas <email@example.com>,
Chris Browy <firstname.lastname@example.org>,
Linux ACPI <email@example.com>,
"Schofield, Alison" <firstname.lastname@example.org>,
Vishal L Verma <email@example.com>,
"Weiny, Ira" <firstname.lastname@example.org>,
Lorenzo Pieralisi <email@example.com>,
Linuxarm <firstname.lastname@example.org>, Fangjian <email@example.com>
Subject: Re: [RFC PATCH 2/2] cxl/mem: Add CDAT table reading from DOE
Date: Mon, 15 Mar 2021 15:00:08 -0700 [thread overview]
Message-ID: <CAPcyv4jq-KovQcEqesA=kCdzdDNtQ9y8g2aBCSXqQv7cvmABtg@mail.gmail.com> (raw)
On Wed, Mar 10, 2021 at 10:15 AM Jonathan Cameron
> On Thu, 11 Mar 2021 02:03:06 +0800
> Jonathan Cameron <Jonathan.Cameron@huawei.com> wrote:
> > This patch simply provides some debug print outs of the entries
> > at probe time + a sysfs binary attribute to allow dumping of the
> > whole table.
> > Binary dumping is modelled on /sys/firmware/ACPI/tables/
> > The ability to dump this table will be very useful for emulation of
> > real devices once they become available as QEMU CXL type 3 device
> > emulation will be able to load this file in.
> > Open questions:
> > * No support here for table updates. Worth including these from the
> > start, or leave that complexity for later?
> > * Worth logging the reported info for debug, or is the binary attribute
> > sufficient? Larger open question of whether to expose this info to
> > userspace or not left for another day!
> > * Where to put the CDAT file? Is it worth a subdirectory?
> > * What is maximum size of the SSLBIS entry - I haven't quite managed
> > to figure that out and this is the record with largest size.
> > We could support dynamic allocation of the record size, but it
> > would add complexity that seems unnecessary.
> > It would not be compliant with the specification for a type 3 memory
> > device to report this record anyway so I'm not that worried about this
> > for now. It will become relevant once we have support for reading
> > CDAT from CXL switches.
> > * cdat.h is formatted in a similar style to pci_regs.h on basis that
> > it may well be helpful to share this header with userspace tools.
> > * Move the generic parts of this out to driver/cxl/cdat.c or leave that
> > until we have other CXL drivers wishing to use this?
> Naturally I remembered another open question within 10 seconds of sending :(
> * Do we want to add any sort of header to the RAW dump of CDAT to aid
> tooling? Whilst it looks a little like an ACPI table it doesn't have
> a signature.
> My gut feeling is no, because the CDAT specification doesn't define one but
> I can see that it might be very convenient to have something that identified
> the data once it was put in a file.
I'm not yet convinced raw dumping is worth it for the same reason that
command payload logging was eliminated from the v5.12-rc1 submission.
There's not much userspace can do with the information besides debug
the kernel behavior. If the kernel assigns a numa node to target a
given CXL memory range with NUMA apis then HMEM_REPORTING should
enumerate the properties. In other words, don't expand the userspace
ABI problem, funnel users to the canonical source for such data.
next prev parent reply other threads:[~2021-03-15 22:01 UTC|newest]
Thread overview: 23+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-03-10 18:03 [RFC PATCH 0/2] PCI Data Object Exchange support + CXL CDAT Jonathan Cameron
2021-03-10 18:03 ` [RFC PATCH 1/2] PCI/doe: Initial support PCI Data Object Exchange Jonathan Cameron
2021-03-15 19:45 ` Dan Williams
2021-03-16 16:29 ` Jonathan Cameron
2021-03-16 16:57 ` Jonathan Cameron
2021-03-16 18:14 ` Dan Williams
2021-03-16 23:26 ` Chris Browy
2021-03-18 1:30 ` Dan Williams
2021-03-18 14:25 ` Jonathan Cameron
2021-06-17 17:12 ` Jonathan Cameron
2021-06-17 19:48 ` Chris Browy
2021-03-23 18:22 ` Jonathan Cameron
2021-03-23 18:57 ` Dan Williams
2021-03-10 18:03 ` [RFC PATCH 2/2] cxl/mem: Add CDAT table reading from DOE Jonathan Cameron
2021-03-10 18:14 ` Jonathan Cameron
2021-03-10 22:59 ` Chris Browy
2021-03-15 22:00 ` Dan Williams [this message]
2021-03-16 10:36 ` Jonathan Cameron
2021-03-17 1:42 ` Dan Williams
2021-03-17 1:55 ` Dan Williams
[not found] <CAAJ9+9fq1=EcOaSoo3oD_5QjYNAv6PPDjKS+gC9o7XDp2p1XpQ@mail.gmail.com>
2022-01-12 22:16 ` Zayd Qumsieh
2022-01-13 9:25 ` Jonathan Cameron
2022-01-15 0:15 ` Zayd Qumsieh
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