[PATCH v2 00/24] x86/resctrl: Merge the CDP resources

James Morse
2021-03-12T18:00:02Z

Hi folks,

Thanks to Reinette and Jamie for the comments on v1. Major changes in v2 are
to keep the closid in resctrl_arch_update_domains(), eliminating one patch,
splitting another that was making two sorts of change, and to re-order the
first few patches. See each patches changelog for more.
----

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 what becomes 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.

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 v5.12-rc2, and can be retrieved from:
git://git.kernel.org/pub/scm/linux/kernel/git/morse/linux.git mpam/resctrl_merge_cdp/v2

v1 was posted here:
https://lore.kernel.org/lkml/20201030161120.227225-1-james.morse@arm.com/

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 a separate schema list for resctrl
x86/resctrl: Pass the schema in info dir's private pointer
x86/resctrl: Label the resources with their configuration type
x86/resctrl: Walk the resctrl schema list instead of an arch list
x86/resctrl: Store the effective num_closid in the schema
x86/resctrl: Add resctrl_arch_get_num_closid()
x86/resctrl: Pass the schema to resctrl filesystem functions
x86/resctrl: Swizzle rdt_resource and resctrl_schema in
pseudo_lock_region
x86/resctrl: Move the schemata names into struct resctrl_schema
x86/resctrl: Group staged configuration into a separate struct
x86/resctrl: Allow different CODE/DATA configurations to be staged
x86/resctrl: Rename update_domains() resctrl_arch_update_domains()
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 ctrl_val arrays
x86/resctrl: Remove rdt_cdp_peer_get()
x86/resctrl: Merge the CDP resources

arch/x86/kernel/cpu/resctrl/core.c | 272 +++++--------
arch/x86/kernel/cpu/resctrl/ctrlmondata.c | 164 +++++---
arch/x86/kernel/cpu/resctrl/internal.h | 218 +++--------
arch/x86/kernel/cpu/resctrl/monitor.c | 44 ++-
arch/x86/kernel/cpu/resctrl/pseudo_lock.c | 12 +-
arch/x86/kernel/cpu/resctrl/rdtgroup.c | 447 ++++++++++++----------
include/linux/resctrl.h | 176 +++++++++
7 files changed, 741 insertions(+), 592 deletions(-)

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2.30.0