[PATCH v7 12/12] Documentation/x86: Update resctrl.rst for new features

Babu Moger
2022-10-17T22:29:14Z

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 of 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 | 139 ++++++++++++++++++++++++++++++++++++++++-
1 file changed, 137 insertions(+), 2 deletions(-)

diff --git a/Documentation/x86/resctrl.rst b/Documentation/x86/resctrl.rst
index 71a531061e4e..d0b4e1a2cb8d 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 +163,79 @@ with the following files:
"mon_features":
Lists the monitoring events if
monitoring is enabled for the resource.
+ Example::
+
+ # 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. 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
+
+"mbm_total_config", "mbm_local_config":
+ These files contain 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.
+ The event configuration settings are domain specific and will affect
+ all the CPUs in the domain.
+
+ 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.
+
+ Examples:
+
+ * To view the current configuration::
+ ::
+
+ # cat /sys/fs/resctrl/info/L3_MON/mbm_total_config
+ 0=0x7f;1=0x7f;2=0x7f;3=0x7f
+
+ # cat /sys/fs/resctrl/info/L3_MON/mbm_local_config
+ 0=0x15;1=0x15;3=0x15;4=0x15
+
+ * To change the mbm_total_bytes to count only reads on domain 0,
+ the bits 0, 1, 4 and 5 needs to be set, which is 110011b in binary
+ (in hexadecimal 0x33):
+ ::
+
+ # echo "0=0x33" > /sys/fs/resctrl/info/L3_MON/mbm_total_config
+
+ # cat /sys/fs/resctrl/info/L3_MON/mbm_total_config
+ 0=0x33;1=0x7f;2=0x7f;3=0x7f
+
+ * To change the mbm_local_bytes to count all the slow memory reads
+ on domain 1, the bits 4 and 5 needs to be set, which is 110000b
+ in binary (in hexadecimal 0x30):
+ ::
+
+ # echo "1=0x30" > /sys/fs/resctrl/info/L3_MON/mbm_local_config
+
+ # cat /sys/fs/resctrl/info/L3_MON/mbm_local_config
+ 0=0x15;1=0x30;3=0x15;4=0x15

"max_threshold_occupancy":
Read/write file provides the largest value (in
@@ -464,6 +539,26 @@ Memory bandwidth domain is L3 cache.

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

+Slow Memory bandwidth Allocation (SMBA)
+---------------------------------------
+AMD hardwares support Slow Memory bandwidth Allocation (SMBA) feature.
+Currently, CXL.memory is the only supported "slow" memory device.
+With the support of SMBA, the hardware enables bandwidth allocation
+on the slow memory devices. If there are multiple such devices in the
+system, the throttling logic groups all the slow sources together
+and applies the limit on them as a whole.
+
+The presence of SMBA (with CXL.memory) is independent of slow memory
+devices presence. If there is no such devices on the system, then
+setting the configuring SMBA will have no impact on the performance
+of the system.
+
+The bandwidth domain for slow memory is L3 cache. Its schemata file
+is formatted as:
+::
+
+ 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 +574,46 @@ 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 current bandwidth limit on all
+domains. The allocated resources are in multiples of one eighth GB/s.
+When writing to the file, you need to specify what cache id you wish to
+configure the bandwidth limit.
+
+For example, to allocate 2GB/s limit on the first cache id:
+
+::
+
+ # 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 SMBA feature
+--------------------------------------------------------------------
+Reading and writing the schemata file is the same as without SMBA in
+above section.
+
+For example, to allocate 8GB/s limit on the first cache id:
+
+::
+
+ # 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