[PATCH v3 0/5] CXL 3.0 Performance Monitoring Unit support

From: Jonathan Cameron
Date: Mon Mar 27 2023 - 13:04:39 EST


v3: Build fixes. Called out in individual patches.

Reported-by: kernel test robot <lkp@xxxxxxxxx>
Link: https://lore.kernel.org/oe-kbuild-all/202303250419.FANh4fIC-lkp@xxxxxxxxx/
Link: https://lore.kernel.org/oe-kbuild-all/202303250523.JdddC4Ld-lkp@xxxxxxxxx/
Link: https://lore.kernel.org/oe-kbuild-all/202303250546.ijiFKIpM-lkp@xxxxxxxxx/
etc

Thanks to all those who have looked at v1, and Kan Liang in particular for
all the feedback on the main driver.

Updated cover letter.

The CXL rev 3.0 specification introduces a CXL Performance Monitoring
Unit definition. CXL components may have any number of these blocks. The
definition is highly flexible, but that does bring complexity in the
driver.

Notes.

1) The QEMU model against which this was developed needs tidying up.
Latest tree at https://gitlab.com/jic23/qemu branch cxl-2023-02-28
It's backed up behind other series that I plan to upstream first.
2) There are quite a lot of corner cases that will need working through
with variants of the model, or I'll have to design a pathological
set of CPMUs to hit all the corner cases in one go. So whilst I believe
the driver should be fine for what it supports we may find issues
as those corners of what is allowed are explored.
3) I'm not sure it makes sense to hang this of the cxl/pci driver but
couldn't really figure out where else in the current structure we could
make it fit cleanly.
4) Driver location. In past perf maintainers have requested perf drivers
for PCI etc be under drivers/perf. That would require moving some
CXL headers to be more generally visible, but is certainly possible
if there is agreement between CXL and perf maintainers on the correct
location.
5) Patch 1 led to a discussion of how to handle the self describing
and extensible nature of the CPMU counters. That is likely to involve
a description in the "caps" sysfs directory and perf tool code that is
aware of the different event combinations that make sense and can
establish which sets are available on a given device.
That is likely to take a while to converge on, so as the driver is useful
in the current state, I'm looking to upstream this first and deal with
the more complex handling later.
6) There is a lot of other functionality that can be added in future
include allowing for simpler hardware implementations that may not
support the minimum level of features currently required by the driver
(freeze, overflow interrupts etc).

CXL rev 3.0 specification available from https://www.computeexpresslink.org

Jonathan Cameron (5):
cxl: Add function to count regblocks of a given type
perf: Allow a PMU to have a parent
cxl/pci: Find and register CXL PMU devices
cxl: CXL Performance Monitoring Unit driver
docs: perf: Minimal introduction the the CXL PMU device and driver

Documentation/admin-guide/perf/cxl.rst | 65 ++
Documentation/admin-guide/perf/index.rst | 1 +
drivers/cxl/Kconfig | 13 +
drivers/cxl/Makefile | 1 +
drivers/cxl/core/Makefile | 1 +
drivers/cxl/core/core.h | 1 +
drivers/cxl/core/cpmu.c | 72 ++
drivers/cxl/core/pci.c | 2 +-
drivers/cxl/core/port.c | 4 +-
drivers/cxl/core/regs.c | 50 +-
drivers/cxl/cpmu.c | 939 +++++++++++++++++++++++
drivers/cxl/cpmu.h | 56 ++
drivers/cxl/cxl.h | 17 +-
drivers/cxl/cxlpci.h | 1 +
drivers/cxl/pci.c | 27 +-
include/linux/perf_event.h | 1 +
kernel/events/core.c | 1 +
17 files changed, 1244 insertions(+), 8 deletions(-)
create mode 100644 Documentation/admin-guide/perf/cxl.rst
create mode 100644 drivers/cxl/core/cpmu.c
create mode 100644 drivers/cxl/cpmu.c
create mode 100644 drivers/cxl/cpmu.h

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