[PATCH v4 13/13] Documentation/x86: Update resctrl_ui.rst for new features

Babu Moger
2022-09-07T18:03:23Z

Update the documentation for the new features:
1. Slow Memory Bandwidth allocation (SMBA).
With this feature, the QOS enforcement policies can be applied
to the external slow memory connected to the host. QOS enforcement
is accomplished by assigning a Class Of Service (COS) to a processor
and specifying allocations or limits for that COS for each resource
to be allocated.

2. Bandwidth Monitoring Event Configuration (BMEC).
The bandwidth monitoring events mbm_total_bytes and mbm_local_bytes
are set to count all the total and local reads/writes respectively.
With the introduction of slow memory, the two counters are not
enough to count all the different types are memory events. With the
feature BMEC, the users have the option to configure mbm_total_bytes
and mbm_local_bytes to count the specific type of events.

Also add configuration instructions with examples.

Signed-off-by: Babu Moger <babu.moger@amd.com>
---
Documentation/x86/resctrl.rst | 148 ++++++++++++++++++++++++++++++++++++++++-
1 file changed, 146 insertions(+), 2 deletions(-)

diff --git a/Documentation/x86/resctrl.rst b/Documentation/x86/resctrl.rst
index 71a531061e4e..56581587c1a3 100644
--- a/Documentation/x86/resctrl.rst
+++ b/Documentation/x86/resctrl.rst
@@ -17,14 +17,16 @@ AMD refers to this feature as AMD Platform Quality of Service(AMD QoS).
This feature is enabled by the CONFIG_X86_CPU_RESCTRL and the x86 /proc/cpuinfo
flag bits:

-============================================= ================================
+=============================================== ================================
RDT (Resource Director Technology) Allocation "rdt_a"
CAT (Cache Allocation Technology) "cat_l3", "cat_l2"
CDP (Code and Data Prioritization) "cdp_l3", "cdp_l2"
CQM (Cache QoS Monitoring) "cqm_llc", "cqm_occup_llc"
MBM (Memory Bandwidth Monitoring) "cqm_mbm_total", "cqm_mbm_local"
MBA (Memory Bandwidth Allocation) "mba"
-============================================= ================================
+SMBA (Slow Memory Bandwidth Allocation) "smba"
+BMEC (Bandwidth Monitoring Event Configuration) "bmec"
+=============================================== ================================

To use the feature mount the file system::

@@ -161,6 +163,23 @@ with the following files:
"mon_features":
Lists the monitoring events if
monitoring is enabled for the resource.
+ Example output:
+
+ # cat /sys/fs/resctrl/info/L3_MON/mon_features
+ llc_occupancy
+ mbm_total_bytes
+ mbm_local_bytes
+
+ If the system supports Bandwidth Monitoring Event
+ Configuration (BMEC), then the bandwidth events will
+ be configurable. Then the output will be.
+
+ # cat /sys/fs/resctrl/info/L3_MON/mon_features
+ llc_occupancy
+ mbm_total_bytes
+ mbm_total_config
+ mbm_local_bytes
+ mbm_local_config

"max_threshold_occupancy":
Read/write file provides the largest value (in
@@ -264,6 +283,32 @@ When monitoring is enabled all MON groups will also contain:
the sum for all tasks in the CTRL_MON group and all tasks in
MON groups. Please see example section for more details on usage.

+"mbm_total_config", "mbm_local_config":
+ This contains the current event configuration for the events
+ mbm_total_bytes and mbm_local_bytes, respectively, when the
+ Bandwidth Monitoring Event Configuration (BMEC) feature is supported.
+ These files are organized by L3 domains under the subdirectories
+ "mon_L3_00" and "mon_L3_01". When BMEC is supported, the events
+ mbm_local_bytes and mbm_total_bytes are configurable.
+
+ Following are the types of events supported:
+
+ ==== ========================================================
+ Bits Description
+ ==== ========================================================
+ 6 Dirty Victims from the QOS domain to all types of memory
+ 5 Reads to slow memory in the non-local NUMA domain
+ 4 Reads to slow memory in the local NUMA domain
+ 3 Non-temporal writes to non-local NUMA domain
+ 2 Non-temporal writes to local NUMA domain
+ 1 Reads to memory in the non-local NUMA domain
+ 0 Reads to memory in the local NUMA domain
+ ==== ========================================================
+
+ By default, the mbm_total_bytes configuration is set to 0x7F to count
+ all the event types and the mbm_local_bytes configuration is set to
+ 0x15 to count all the local memory events.
+
Resource allocation rules
-------------------------

@@ -464,6 +509,19 @@ Memory bandwidth domain is L3 cache.

MB:<cache_id0>=bw_MBps0;<cache_id1>=bw_MBps1;...

+Slow Memory bandwidth Allocation (when supported)
+-------------------------------------------------
+Currently, CXL.memory is the only supported "slow" memory device.
+With the support of SMBA feature the hardware enables bandwidth
+allocation on the slow memory devices. If there are multiple slow
+memory devices in the system, then the throttling logic groups all
+the slow sources together and applies the limit on them as a whole.
+
+Slow Memory b/w domain is L3 cache.
+::
+
+ SMBA:<cache_id0>=bandwidth0;<cache_id1>=bandwidth1;...
+
Reading/writing the schemata file
---------------------------------
Reading the schemata file will show the state of all resources
@@ -479,6 +537,44 @@ which you wish to change. E.g.
L3DATA:0=fffff;1=fffff;2=3c0;3=fffff
L3CODE:0=fffff;1=fffff;2=fffff;3=fffff

+Reading/writing the schemata file (on AMD systems)
+--------------------------------------------------
+Reading the schemata file will show the state of all resources
+on all domains. When writing the memory bandwidth allocation you
+only need to specify those values in an absolute number expressed
+in 1/8 GB/s increments. To allocate bandwidth limit of 2GB, you
+need to specify the value 16 (16 * 1/8 = 2). E.g.
+::
+
+ # cat schemata
+ MB:0=2048;1=2048;2=2048;3=2048
+ L3:0=ffff;1=ffff;2=ffff;3=ffff
+
+ # echo "MB:1=16" > schemata
+ # cat schemata
+ MB:0=2048;1= 16;2=2048;3=2048
+ L3:0=ffff;1=ffff;2=ffff;3=ffff
+
+Reading/writing the schemata file (on AMD systems) with slow memory
+-------------------------------------------------------------------
+Reading the schemata file will show the state of all resources
+on all domains. When writing the memory bandwidth allocation you
+only need to specify those values in an absolute number expressed
+in 1/8 GB/s increments. To allocate bandwidth limit of 8GB, you
+need to specify the value 64 (64 * 1/8 = 8). E.g.
+::
+
+ # cat schemata
+ SMBA:0=2048;1=2048;2=2048;3=2048
+ MB:0=2048;1=2048;2=2048;3=2048
+ L3:0=ffff;1=ffff;2=ffff;3=ffff
+
+ # echo "SMBA:1=64" > schemata
+ # cat schemata
+ SMBA:0=2048;1= 64;2=2048;3=2048
+ MB:0=2048;1=2048;2=2048;3=2048
+ L3:0=ffff;1=ffff;2=ffff;3=ffff
+
Cache Pseudo-Locking
====================
CAT enables a user to specify the amount of cache space that an
@@ -1210,6 +1306,54 @@ View the llc occupancy snapshot::
# cat /sys/fs/resctrl/p1/mon_data/mon_L3_00/llc_occupancy
11234000

+Example 5 (Configure and Monitor specific event types)
+------------------------------------------------------
+
+A single socket system which has real time tasks running on cores 0-4
+and non real time tasks on other CPUs. We want to monitor the memory
+bandwidth allocation for specific events.
+::
+
+ # mount -t resctrl resctrl /sys/fs/resctrl
+ # cd /sys/fs/resctrl
+ # mkdir p1
+
+Move the CPUs 0-4 over to p1::
+
+ # echo 0xf > p1/cpus
+
+View the current mbm_local_bytes::
+
+ # cat /sys/fs/resctrl/p1/mon_data/mon_L3_00/mbm_local_bytes
+ 112501
+
+Change the mbm_local_bytes to count mon-temporal writes to both local
+and non-local NUMA domain. Refer to event supported bitmap under
+mbm_local_config::
+
+ # echo 0xc > /sys/fs/resctrl/p1/mon_data/mon_L3_00/mbm_local_config
+
+View the updated mbm_local_bytes::
+
+ # cat /sys/fs/resctrl/p1/mon_data/mon_L3_00/mbm_local_bytes
+ 12601
+
+Similar experiment on mbm_total_bytes. First view the current mbm_total_bytes::
+
+ # cat /sys/fs/resctrl/p1/mon_data/mon_L3_00/mbm_total_bytes
+ 1532501
+
+Change the mbm_total_bytes to count only reads to slow memory on both local
+and non-local NUMA domain. Refer to event supported bitmap under
+mbm_total_config::
+
+ # echo 0x30 > /sys/fs/resctrl/p1/mon_data/mon_L3_00/mbm_total_config
+
+View the updated mbm_total_bytes::
+
+ # cat /sys/fs/resctrl/p1/mon_data/mon_L3_00/mbm_total_bytes
+ 104562
+
Intel RDT Errata
================