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Subject[PATCH 13/32] Documentation, x86: Documentation for Intel resource allocation user interface
Date
From: Fenghua Yu <fenghua.yu@intel.com>

The documentation describes user interface of how to allocate resource
in Intel RDT.

Please note that the documentation covers generic user interface. Current
patch set code only implemente CAT L3. CAT L2 code will be sent later.

Signed-off-by: Fenghua Yu <fenghua.yu@intel.com>
Reviewed-by: Tony Luck <tony.luck@intel.com>
---
Documentation/x86/intel_rdt_ui.txt | 268 +++++++++++++++++++++++++++++++++++++
1 file changed, 268 insertions(+)
create mode 100644 Documentation/x86/intel_rdt_ui.txt

diff --git a/Documentation/x86/intel_rdt_ui.txt b/Documentation/x86/intel_rdt_ui.txt
new file mode 100644
index 0000000..c52baf5
--- /dev/null
+++ b/Documentation/x86/intel_rdt_ui.txt
@@ -0,0 +1,268 @@
+User Interface for Resource Allocation in Intel Resource Director Technology
+
+Copyright (C) 2016 Intel Corporation
+
+Fenghua Yu <fenghua.yu@intel.com>
+
+We create a new file system rscctrl in /sys/fs as user interface for Cache
+Allocation Technology (CAT) and future resource allocations in Intel
+Resource Director Technology (RDT). User can allocate cache or other
+resources to tasks or cpus through this interface.
+
+CONTENTS
+========
+
+ 1. Terms
+ 2. Mount rscctrl file system
+ 3. Hierarchy in rscctrl
+ 4. Create and remove sub-directory
+ 5. Add/remove a task in a partition
+ 6. Add/remove a CPU in a partition
+ 7. Some usage examples
+
+
+1. Terms
+========
+
+We use the following terms and concepts in this documentation.
+
+RDT: Intel Resoure Director Technology
+
+CAT: Cache Allocation Technology
+
+CDP: Code and Data Prioritization
+
+CBM: Cache Bit Mask
+
+Cache ID: A cache identification. It is unique in one cache index on the
+platform. User can find cache ID in cache sysfs interface:
+/sys/devices/system/cpu/cpu*/cache/index*/id
+
+Share resource domain: A few different resources can share same QoS mask
+MSRs array. For example, one L2 cache can share QoS MSRs with its next level
+L3 cache. A domain number represents the L2 cache, the L3 cache, the L2
+cache's shared cpumask, and the L3 cache's shared cpumask.
+
+2. Mount rscctrl file system
+============================
+
+Like other file systems, the rscctrl file system needs to be mounted before
+it can be used.
+
+mount -t rscctrl rscctrl <-o cdp,verbose> /sys/fs/rscctrl
+
+This command mounts the rscctrl file system under /sys/fs/rscctrl.
+
+Options are optional:
+
+cdp: Enable Code and Data Prioritization (CDP). Without the option, CDP
+is disabled.
+
+verbose: Output more info in the "info" file under info directory and in
+dmesg. This is mainly for debug.
+
+
+3. Hierarchy in rscctrl
+=======================
+
+The initial hierarchy of the rscctrl file system is as follows after mount:
+
+/sys/fs/rscctrl/info/info
+ /<resource0>/<resource0 specific info files>
+ /<resource1>/<resource1 specific info files>
+ ....
+ /tasks
+ /cpus
+ /schemas
+
+There are a few files and sub-directories in the hierarchy.
+
+3.1. info
+---------
+
+The read-only sub-directory "info" in root directory has RDT related
+system info.
+
+The "info" file under the info sub-directory shows general info of the system.
+It shows shared domain and the resources within this domain.
+
+Each resource has its own info sub-directory. User can read the information
+for allocation. For example, l3 directory has max_closid, max_cbm_len,
+domain_to_cache_id.
+
+3.2. tasks
+----------
+
+The file "tasks" has all task ids in the root directory initially. The
+thread ids in the file will be added or removed among sub-directories or
+partitions. A task id only stays in one directory at the same time.
+
+3.3. cpus
+
+The file "cpus" has a cpu mask that specifies the CPUs that are bound to the
+schemas. Any tasks scheduled on the cpus will use the schemas. User can set
+both "cpus" and "tasks" to share the same schema in one directory. But when
+a CPU is bound to a schema, a task running on the CPU uses this schema and
+kernel will ignore scheam set up for the task in "tasks".
+
+Initial value is all zeros which means there is no CPU bound to the schemas
+in the root directory and tasks use the schemas.
+
+3.4. schemas
+------------
+
+The file "schemas" has default allocation masks/values for all resources on
+each socket/cpu. Format of the file "schemas" is in multiple lines and each
+line represents masks or values for one resource.
+
+Format of one resource schema line is as follows:
+
+<resource name>:<resource id0>=<schema>;<resource id1>=<schema>;...
+
+As one example, CAT L3's schema format is:
+
+L3:<cache_id0>=<cbm>;<cache_id1>=<cbm>;...
+
+On a two socket machine, L3's schema line could be:
+
+L3:0=ff;1=c0
+
+which means this line in "schemas" file is for CAT L3, L3 cache id 0's CBM
+is 0xff, and L3 cache id 1's CBM is 0xc0.
+
+If one resource is disabled, its line is not shown in schemas file.
+
+The schema line can be expended for situations. L3 cbms format can be
+expended to CDP enabled L3 cbms format:
+
+L3:<cache_id0>=<d_cbm>,<i_cbm>;<cache_id1>=<d_cbm>,<i_cbm>;...
+
+Initial value is all ones which means all tasks use all resources initially.
+
+4. Create and remove sub-directory
+===================================
+
+User can create a sub-directory under the root directory by "mkdir" command.
+User can remove the sub-directory by "rmdir" command.
+
+Each sub-directory represents a resource allocation policy that user can
+allocate resources for tasks or cpus.
+
+Each directory has three files "tasks", "cpus", and "schemas". The meaning
+of each file is same as the files in the root directory.
+
+When a directory is created, initial contents of the files are:
+
+tasks: Empty. This means no task currently uses this allocation schemas.
+cpus: All zeros. This means no CPU uses this allocation schemas.
+schemas: All ones. This means all resources can be used in this allocation.
+
+5. Add/remove a task in a partition
+===================================
+
+User can add/remove a task by writing its PID in "tasks" in a partition.
+User can read PIDs stored in one "tasks" file.
+
+One task PID only exists in one partition/directory at the same time. If PID
+is written in a new directory, it's removed automatically from its last
+directory.
+
+6. Add/remove a CPU in a partition
+==================================
+
+User can add/remove a CPU by writing its bit in "cpus" in a partition.
+User can read CPUs stored in one "cpus" file.
+
+One CPU only exists in one partition/directory if user wants it to be bound
+to any "schemas". Kernel guarantees uniqueness of the CPU in the whole
+directory to make sure it only uses one schemas. If a CPU is written in one
+new directory, it's automatically removed from its original directory if it
+exists in the original directory.
+
+Or it doesn't exist in the whole directory if user doesn't bind it to any
+"schemas".
+
+7. Some usage examples
+======================
+
+7.1 Example 1 for sharing CLOSID on socket 0 between two partitions
+
+Only L3 cbm is enabled. Assume the machine is 2-socket and dual-core without
+hyperthreading.
+
+#mount -t rscctrl rscctrl /sys/fs/rscctrl
+#cd /sys/fs/rscctrl
+#mkdir p0 p1
+#echo "L3:0=3;1=c" > /sys/fs/rscctrl/p0/schemas
+#echo "L3:0=3;1=3" > /sys/fs/rscctrl/p1/schemas
+
+In partition p0, kernel allocates CLOSID 0 for L3 cbm=0x3 on socket 0 and
+CLOSID 0 for cbm=0xc on socket 1.
+
+In partition p1, kernel allocates CLOSID 0 for L3 cbm=0x3 on socket 0 and
+CLOSID 1 for cbm=0x3 on socket 1.
+
+When p1/schemas is updated for socket 0, kernel searches existing
+IA32_L3_QOS_MASK_n MSR registers and finds that 0x3 is in IA32_L3_QOS_MASK_0
+register already. Therefore CLOSID 0 is shared between partition 0 and
+partition 1 on socket 0.
+
+When p1/schemas is udpated for socket 1, kernel searches existing
+IA32_L3_QOS_MASK_n registers and doesn't find a matching cbm. Therefore
+CLOSID 1 is created and IA32_L3_QOS_MASK_1=0xc.
+
+7.2 Example 2 for allocating L3 cache for real-time apps
+
+Two real time tasks pid=1234 running on processor 0 and pid=5678 running on
+processor 1 on socket 0 on a 2-socket and dual core machine. To avoid noisy
+neighbors, each of the two real-time tasks exclusively occupies one quarter
+of L3 cache on socket 0. Assume L3 cbm max width is 20 bits.
+
+#mount -t rscctrl rscctrl /sys/fs/rscctrl
+#cd /sys/fs/rscctrl
+#mkdir p0 p1
+#taskset 0x1 1234
+#taskset 0x2 5678
+#cd /sys/fs/rscctrl/
+#edit schemas to have following allocation:
+L3:0=3ff;1=fffff
+
+which means that all tasks use whole L3 cache 1 and half of L3 cache 0.
+
+#cd ..
+#mkdir p1 p2
+#cd p1
+#echo 1234 >tasks
+#edit schemas to have following two lines:
+L3:0=f8000;1=fffff
+
+which means task 1234 uses L3 cbm=0xf8000, i.e. one quarter of L3 cache 0
+and whole L3 cache 1.
+
+Since 1234 is tied to processor 0, it actually uses the quarter of L3
+on socket 0 only.
+
+#cd ../p2
+#echo 5678 >tasks
+#edit schemas to have following two lines:
+L3:0=7c00;1=fffff
+
+Which means that task 5678 uses L3 cbm=0x7c00, another quarter of L3 cache 0
+and whole L3 cache 1.
+
+Since 5678 is tied to processor 1, it actually only uses the quarter of L3
+on socket 0.
+
+Internally three CLOSIDs are allocated on L3 cache 0:
+IA32_L3_QOS_MASK_0 = 0x3ff
+IA32_L3_QOS_MASK_1 = 0xf8000
+IA32_L3_QOS_MASK_2 = 0x7c00.
+
+Each CLOSID's reference count=1 on L3 cache 0. There is no shared cbms on
+cache 0.
+
+Only one CLOSID is allocated on L3 cache 1:
+
+IA32_L3_QOS_MASK_0=0xfffff. It's shared by root, p1 and p2.
+
+Therefore CLOSID 0's reference count=3 on L3 cache 1.
--
2.5.0
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