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SubjectRe: [PATCH 13/32] Documentation, x86: Documentation for Intel resource allocation user interface
On Tue, Jul 12, 2016 at 06:02:46PM -0700, Fenghua Yu wrote:
> 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".
schema
> +
> +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

This interface addresses the previously listed needs for
multiple VMs with realtime tasks sharing L3 cache.

Thanks.

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