[PATCH V10 00/10] New cpumask API and Intel Cache Allocation support
From: Vikas Shivappa
Date: Tue Jun 23 2015 - 18:59:30 EST
This patch has some preparatory patches which add a new API
cpumask_any_online_but and change hot cpu handling code in existing
cache monitoring and RAPL kernel code. This improves hot cpu
notification handling by not looping through all online cpus which could
be expensive in large systems.
Cache allocation patches(dependent on prep patches) adds a cgroup
subsystem to support the new Cache Allocation feature found in future
Intel Xeon Intel processors. Cache Allocation is a sub-feature with in
Resource Director Technology(RDT) feature. RDT which provides support to
control sharing of platform resources like L3 cache.
Cache Allocation Technology provides a way for the Software (OS/VMM) to
restrict cache allocation to a defined 'subset' of cache which may be
overlapping with other 'subsets'. This feature is used when allocating
a line in cache ie when pulling new data into the cache. The
programming of the h/w is done via programming MSRs. The patch series
support to perform L3 cache allocation.
In todays new processors the number of cores is continuously increasing
which in turn increase the number of threads or workloads that can
simultaneously be run. When multi-threaded applications run
concurrently, they compete for shared resources including L3 cache. At
times, this L3 cache resource contention may result in inefficient space
utilization. For example a higher priority thread may end up with lesser
L3 cache resource or a cache sensitive app may not get optimal cache
occupancy thereby degrading the performance. Cache Allocation kernel
patch helps provides a framework for sharing L3 cache so that users can
allocate the resource according to set requirements.
More information about the feature can be found in the Intel SDM, Volume
3 section 17.15. SDM does not yet use the 'RDT' term yet and it is
planned to be changed at a later time.
*All the patches will apply on tip/perf/core*.
Changes in V10:
- changed the hot cpu notification we handle in cqm and cache allocation
to cpu_online and cpu_dead and removed others as the
cpu_*_prepare also had corresponding cancel notification
which we did not handle.
- changed the file in rdt cgroup to l3_cache_mask to represent that its
for l3 cache.
Changes as per Thomas and PeterZ feedback:
- fixed the cpumask declarations in cpumask.h and rdt,cmt and rapl to
have static so that they burden stack space when large.
- fixed incorrect usage of mutex during cpu_starting notifications as
interrupts are disabled and nothing else can be scheduled, handling
cpu_online instead of cpu_starting.
- changed name from hsw_probetest to cache_alloc_hsw_probe.
- changed x86_rdt_max_closid to x86_cache_max_closid and
x86_rdt_max_cbm_len to x86_cache_max_cbm_len as they are only related
to cache allocation and not to all rdt.
Changes in V9:
Changes made as per Thomas feedback:
- added a comment where we call schedule in code only when RDT is
- Reordered the local declarations to follow convention in
Changes in V8: Thanks to feedback from Thomas and following changes are
made based on his feedback:
Generic changes/Preparatory patches:
-added a new cpumask_any_online_but which returns the next
core sibling that is online.
-Made changes in Intel Cache monitoring and Intel RAPL(Running average
power limit) code to use the new function above to find the next cpu
that can be a designated reader for the package. Also changed the way
the package masks are computed which can be simplified using
Cache allocation specific changes:
-Moved the documentation to the begining of the patch series.
-Added more documentation for the rdt cgroup files in the documentation.
-Changed the dmesg output when cache alloc is enabled to be more helpful
and updated few other comments to be better readable.
-removed __ prefix to functions like clos_get which were not following
-added code to take action on a WARN_ON in clos_put. Made a few other
changes to reduce code text.
-updated better readable/Kernel doc format comments for the
call to rdt_css_alloc, datastructures .
-changed the names of functions to only have intel_ prefix for external
-replaced (void *)&closid with (void *)closid when calling
-fixed the reference release of closid during cache bitmask write.
-changed the code to not ignore a cache mask which has bits set outside
of the max bits allowed. It returns an error instead.
-replaced bitmap_set(&max_mask, 0, max_cbm_len) with max_mask =
(1ULL << max_cbm) - 1.
- update the rdt_cpu_mask which has one cpu for each package, using
topology_core_cpumask instead of looping through existing rdt_cpu_mask.
Realized topology_core_cpumask name is misleading and it actually
returns the cores in a cpu package!
-arranged the code better to have the code relating to similar task
-Improved searching for the next online cpu sibling and maintaining the
rdt_cpu_mask which has one cpu per package.
-removed the unnecessary wrapper rdt_enabled.
-removed unnecessary spin lock and rculock in the scheduling code.
-merged all scheduling code into one patch not seperating the RDT common
software cache code.
Changes in V7: Based on feedback from PeterZ and Matt and following
- changed lot of naming to reflect the data structures which are common
to RDT and specific to Cache allocation.
- removed all usage of 'cat'. replace with more friendly cache
- fixed lot of convention issues (whitespace, return paradigm etc)
- changed the scheduling hook for RDT to not use a inline.
- removed adding new scheduling hook and just reused the existing one
similar to perf hook.
Changes in V6:
- rebased to 4.1-rc1 which has the CMT(cache monitoring) support included.
- (Thanks to Marcelo's feedback).Fixed support for hot cpu handling for
IA32_L3_QOS MSRs. Although during deep C states the MSR need not be restored
this is needed when physically a new package is added.
-some other coding convention changes including renaming to cache_mask using a
refcnt to track the number of cgroups using a closid in clos_cbm map.
-1b cbm support for non-hsw SKUs. HSW is an exception which needs the cache
bit masks to be at least 2 bits.
Changes in v5:
- Added support to propagate the cache bit mask update for each
- Removed the cache bit mask reference in the intel_rdt structure as
there was no need for that and we already maintain a separate
- Made a few coding convention changes which include adding the
assertion while freeing the CLOSID.
Changes in V4:
- Integrated with the latest V5 CMT patches.
- Changed naming of cgroup to rdt(resource director technology) from
cat(cache allocation technology). This was done as the RDT is the
umbrella term for platform shared resources allocation. Hence in
future it would be easier to add resource allocation to the same
- Naming changes also applied to a lot of other data structures/APIs.
- Added documentation on cgroup usage for cache allocation to address
a lot of questions from various academic and industry regarding
cache allocation usage.
Changes in V3:
- Implements a common software cache for IA32_PQR_MSR
- Implements support for hsw Cache Allocation enumeration. This does not use the brand
strings like earlier version but does a probe test. The probe test is done only
on hsw family of processors
- Made a few coding convention, name changes
- Check for lock being held when ClosID manipulation happens
Changes in V2:
- Removed HSW specific enumeration changes. Plan to include it later as a
- Fixed the code in prep_arch_switch to be specific for x86 and removed
- Fixed cbm_write to not write all 1s when a cgroup is freed.
- Fixed one possible memory leak in init.
- Changed some of manual bitmap
manipulation to use the predefined bitmap APIs to make code more readable
- Changed name in sources from cqe to cat
- Global cat enable flag changed to static_key and disabled cgroup early_init
[PATCH 01/10] cpumask: Introduce cpumask_any_online_but
[PATCH 02/10] x86/intel_cqm: Modify hot cpu notification handling
[PATCH 03/10] x86/intel_rapl: Modify hot cpu notification handling
[PATCH 04/10] x86/intel_rdt: Cache Allocation documentation and
[PATCH 05/10] x86/intel_rdt: Add support for Cache Allocation
[PATCH 06/10] x86/intel_rdt: Add new cgroup and Class of service
[PATCH 07/10] x86/intel_rdt: Add support for cache bit mask
[PATCH 08/10] x86/intel_rdt: Implement scheduling support for Intel
[PATCH 09/10] x86/intel_rdt: Hot cpu support for Cache Allocation
[PATCH 10/10] x86/intel_rdt: Intel haswell Cache Allocation
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