[PATCH 00/24] x86/resctrl: Merge the CDP resources

* [PATCH 00/24] x86/resctrl: Merge the CDP resources
@ 2020-10-30 16:10 James Morse
  2020-10-30 16:10 ` [PATCH 01/24] x86/resctrl: Split struct rdt_resource James Morse
                   ` (25 more replies)
  0 siblings, 26 replies; 52+ messages in thread
From: James Morse @ 2020-10-30 16:10 UTC (permalink / raw)
  To: x86, linux-kernel
  Cc: Fenghua Yu, Reinette Chatre, Thomas Gleixner, Ingo Molnar,
	Borislav Petkov, shameerali.kolothum.thodi, Jamie Iles,
	D Scott Phillips OS, James Morse

Hi folks,

This series re-folds the resctrl code so the CDP resources (L3CODE et al)
behaviour is all contained in the filesystem parts, with a minimum amount
of arch specific code.

Arm have some CPU support for dividing caches into portions, and
applying bandwidth limits at various points in the SoC. The collective term
for these features is MPAM: Memory Partitioning and Monitoring.

MPAM is similar enough to Intel RDT, that it should use the defacto linux
interface: resctrl. This filesystem currently lives under arch/x86, and is
tightly coupled to the architecture.
Ultimately, my plan is to split the existing resctrl code up to have an
arch<->fs abstraction, then move all the bits out to fs/resctrl. From there
MPAM can be wired up.

x86 might have two resources with cache controls, (L2 and L3) but has
extra copies for CDP: L{2,3}{CODE,DATA}, which are marked as enabled
if CDP is enabled for the corresponding cache.

MPAM has an equivalent feature to CDP, but its a property of the CPU,
not the cache. Resctrl needs to have x86's odd/even behaviour, as that
its the ABI, but this isn't how the MPAM hardware works. It is entirely
possible that an in-kernel user of MPAM would not be using CDP, whereas
resctrl is.
Pretending L3CODE and L3DATA are entirely separate resources is a neat
trick, but doing this is specific to x86.
Doing this leaves the arch code in control of various parts of the
filesystem ABI: the resources names, and the way the schemata are parsed.
Allowing this stuff to vary between architectures is bad for user space.

This series collapses the CODE/DATA resources, moving all the user-visible
resctrl ABI into the filesystem code. CDP becomes the type of configuration
being applied to a cache. This is done by adding a struct resctrl_schema to
the parts of resctrl that will move to fs. This holds the arch-code resource
that is in use for this schema, along with other properties like the name,
and whether the configuration being applied is CODE/DATA/BOTH.

This lets us fold the extra resources out of the arch code so that they
don't need to be duplicated if the equivalent feature to CDP is missing, or
implemented in a different way.

The first two patches split the resource and domain structs to have an
arch specific 'hw' portion, and the rest that is visible to resctrl.
Future series massage the resctrl code so there are no accesses to 'hw'
structures in the parts of resctrl that will move to fs, providing helpers
where necessary.

Since anyone last looked at this, the CDP property has been made per-resource
instead of global. MPAM will need to make this global in the arch code, as
CODE/DATA closid are based on how the CPU tags traffic, not how the cache
interprets it. resctrl sets CDP enabled on a resource, but reads it back on
each one.
The attempt to keep closids as-used-by-resctrl and closids as-written-to-hw
appart has been dropped.
There are two copies of num_closid. The version private to the arch code is
the value discovered from hardware. resctrl has its own version, which it
may write to, which is exposed to user-space. This lets resctrl do its
odd/even thing, even if thats not how the hardware works.

This series adds temporary scaffolding, which it removes a few patches
later. This is to allow things like the ctrlval arrays and resources to be
merged separately, which should make is easier to bisect. These things
are marked temporary, and should all be gone by the end of the series.

This series is a little rough around the monitors, would a fake
struct resctrl_schema for the monitors simplify things, or be a source
of bugs?

This series is based on v5.10-rc1, and can be retrieved from:
git://git.kernel.org/pub/scm/linux/kernel/git/morse/linux.git mpam/resctrl_merge_cdp/v1

Parts were previously posted as an RFC here:
https://lore.kernel.org/lkml/20200214182947.39194-1-james.morse@arm.com/

Thanks,

James Morse (24):
  x86/resctrl: Split struct rdt_resource
  x86/resctrl: Split struct rdt_domain
  x86/resctrl: Add resctrl_arch_get_num_closid()
  x86/resctrl: Add a separate schema list for resctrl
  x86/resctrl: Pass the schema in resdir's private pointer
  x86/resctrl: Store the effective num_closid in the schema
  x86/resctrl: Label the resources with their configuration type
  x86/resctrl: Walk the resctrl schema list instead of an arch list
  x86/resctrl: Change rdt_resource to resctrl_schema in
    pseudo_lock_region
  x86/resctrl: Move the schema names into struct resctrl_schema
  x86/resctrl: Group staged configuration into a separate struct
  x86/resctrl: Add closid to the staged config
  x86/resctrl: Allow different CODE/DATA configurations to be staged
  x86/resctrl: Make update_domains() learn the affected closids
  x86/resctrl: Add a helper to read a closid's configuration
  x86/resctrl: Add a helper to read/set the CDP configuration
  x86/resctrl: Use cdp_enabled in rdt_domain_reconfigure_cdp()
  x86/resctrl: Pass configuration type to resctrl_arch_get_config()
  x86/resctrl: Make ctrlval arrays the same size
  x86/resctrl: Apply offset correction when config is staged
  x86/resctrl: Calculate the index from the configuration type
  x86/resctrl: Merge the ctrlval arrays
  x86/resctrl: Remove rdt_cdp_peer_get()
  x86/resctrl: Merge the CDP resources

 arch/x86/kernel/cpu/resctrl/core.c        | 290 ++++++--------
 arch/x86/kernel/cpu/resctrl/ctrlmondata.c | 174 ++++++---
 arch/x86/kernel/cpu/resctrl/internal.h    | 215 +++-------
 arch/x86/kernel/cpu/resctrl/monitor.c     |  44 ++-
 arch/x86/kernel/cpu/resctrl/pseudo_lock.c |  12 +-
 arch/x86/kernel/cpu/resctrl/rdtgroup.c    | 454 ++++++++++++----------
 include/linux/resctrl.h                   | 189 +++++++++
 7 files changed, 775 insertions(+), 603 deletions(-)

-- 
2.28.0

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