[PATCH V6 0/7] x86/intel_rdt: Intel Cache Allocation Technology

[Vikas Shivappa]

This patch adds a cgroup subsystem to support the new Cache Allocation 
Technology (CAT) feature found in future Intel Xeon Intel processors. CAT is 
part of Resource Director Technology(RDT) or
Platform Shared resource control which provides support to control
sharing of platform resources like L3 cache.

Cache Allocation Technology(CAT) 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.
CAT 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 4.1-rc0*.

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.
-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 
package.
- Removed the cache bit mask reference in the intel_rdt structure as
  there was no need for that and we already maintain a separate
  closid<->cbm mapping.
- 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 
  cgroup
- 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 CAT 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
  separate patch.  
- Fixed the code in prep_arch_switch to be specific for x86 and removed
  x86 defines.
- 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 1/7] x86/intel_rdt: Intel Cache Allocation Technology detection
[PATCH 2/7] x86/intel_rdt: Adds support for Class of service
[PATCH 3/7] x86/intel_rdt: Support cache bit mask for Intel CAT
[PATCH 4/7] x86/intel_rdt: Implement scheduling support for Intel RDT
[PATCH 5/7] x86/intel_rdt: Software Cache for IA32_PQR_MSR
[PATCH 6/7] x86/intel_rdt: Intel haswell CAT enumeration
[PATCH 7/7] x86/intel_rdt: Add CAT documentation and usage guide
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