[v12,8/8] x86/resctrl: Update documentation with Sub-NUMA cluster changes

Message ID 20231130003418.89964-9-tony.luck@intel.com
State New
Headers
Series Add support for Sub-NUMA cluster (SNC) systems |

Commit Message

Luck, Tony Nov. 30, 2023, 12:34 a.m. UTC
  With Sub-NUMA Cluster mode enabled the scope of monitoring resources is
per-NODE instead of per-L3 cache. Suffixes of directories with "L3" in
their name refer to Sub-NUMA nodes instead of L3 cache ids.

Users should be aware that SNC mode also affects the amount of L3 cache
available for allocation within each SNC node.

Signed-off-by: Tony Luck <tony.luck@intel.com>
Reviewed-by: Peter Newman <peternewman@google.com>
Reviewed-by: Reinette Chatre <reinette.chatre@intel.com>
Reviewed-by: Shaopeng Tan <tan.shaopeng@jp.fujitsu.com>
Tested-by: Shaopeng Tan <tan.shaopeng@jp.fujitsu.com>
---
 Documentation/arch/x86/resctrl.rst | 25 +++++++++++++++++++++----
 1 file changed, 21 insertions(+), 4 deletions(-)
  

Comments

Moger, Babu Dec. 4, 2023, 4:55 p.m. UTC | #1
On 11/29/23 18:34, Tony Luck wrote:
> With Sub-NUMA Cluster mode enabled the scope of monitoring resources is
> per-NODE instead of per-L3 cache. Suffixes of directories with "L3" in
> their name refer to Sub-NUMA nodes instead of L3 cache ids.
> 
> Users should be aware that SNC mode also affects the amount of L3 cache
> available for allocation within each SNC node.
> 
> Signed-off-by: Tony Luck <tony.luck@intel.com>
> Reviewed-by: Peter Newman <peternewman@google.com>
> Reviewed-by: Reinette Chatre <reinette.chatre@intel.com>
> Reviewed-by: Shaopeng Tan <tan.shaopeng@jp.fujitsu.com>
> Tested-by: Shaopeng Tan <tan.shaopeng@jp.fujitsu.com>
> ---
>  Documentation/arch/x86/resctrl.rst | 25 +++++++++++++++++++++----
>  1 file changed, 21 insertions(+), 4 deletions(-)
> 
> diff --git a/Documentation/arch/x86/resctrl.rst b/Documentation/arch/x86/resctrl.rst
> index a6279df64a9d..49ff789db1d8 100644
> --- a/Documentation/arch/x86/resctrl.rst
> +++ b/Documentation/arch/x86/resctrl.rst
> @@ -366,10 +366,10 @@ When control is enabled all CTRL_MON groups will also contain:
>  When monitoring is enabled all MON groups will also contain:
>  
>  "mon_data":
> -	This contains a set of files organized by L3 domain and by
> -	RDT event. E.g. on a system with two L3 domains there will
> -	be subdirectories "mon_L3_00" and "mon_L3_01".	Each of these
> -	directories have one file per event (e.g. "llc_occupancy",
> +	This contains a set of files organized by L3 domain or by NUMA
> +	node (depending on whether Sub-NUMA Cluster (SNC) mode is disabled
> +	or enabled respectively) and by RDT event.  Each of these
> +	directories has one file per event (e.g. "llc_occupancy",
>  	"mbm_total_bytes", and "mbm_local_bytes"). In a MON group these
>  	files provide a read out of the current value of the event for
>  	all tasks in the group. In CTRL_MON groups these files provide
> @@ -478,6 +478,23 @@ if non-contiguous 1s value is supported. On a system with a 20-bit mask
>  each bit represents 5% of the capacity of the cache. You could partition
>  the cache into four equal parts with masks: 0x1f, 0x3e0, 0x7c00, 0xf8000.
>  
> +Notes on Sub-NUMA Cluster mode
> +==============================
> +When SNC mode is enabled Linux may load balance tasks between Sub-NUMA

enabled, Linux

Thanks
Babu

> +nodes much more readily than between regular NUMA nodes since the CPUs
> +on Sub-NUMA nodes share the same L3 cache and the system may report
> +the NUMA distance between Sub-NUMA nodes with a lower value than used
> +for regular NUMA nodes.  Users who do not bind tasks to the CPUs of a
> +specific Sub-NUMA node must read the "llc_occupancy", "mbm_total_bytes",
> +and "mbm_local_bytes" for all Sub-NUMA nodes where the tasks may execute
> +to get the full view of traffic for which the tasks were the source.
> +
> +The cache allocation feature still provides the same number of
> +bits in a mask to control allocation into the L3 cache, but each
> +of those ways has its capacity reduced because the cache is divided
> +between the SNC nodes. The values reported in the resctrl
> +"size" files are adjusted accordingly.
> +
>  Memory bandwidth Allocation and monitoring
>  ==========================================
>
  
Luck, Tony Dec. 4, 2023, 5:51 p.m. UTC | #2
>> +Notes on Sub-NUMA Cluster mode
>> +==============================
>> +When SNC mode is enabled Linux may load balance tasks between Sub-NUMA
>
> enabled, Linux

Babu,

Thanks. I've added that "," ready for next version.

-Tony
  

Patch

diff --git a/Documentation/arch/x86/resctrl.rst b/Documentation/arch/x86/resctrl.rst
index a6279df64a9d..49ff789db1d8 100644
--- a/Documentation/arch/x86/resctrl.rst
+++ b/Documentation/arch/x86/resctrl.rst
@@ -366,10 +366,10 @@  When control is enabled all CTRL_MON groups will also contain:
 When monitoring is enabled all MON groups will also contain:
 
 "mon_data":
-	This contains a set of files organized by L3 domain and by
-	RDT event. E.g. on a system with two L3 domains there will
-	be subdirectories "mon_L3_00" and "mon_L3_01".	Each of these
-	directories have one file per event (e.g. "llc_occupancy",
+	This contains a set of files organized by L3 domain or by NUMA
+	node (depending on whether Sub-NUMA Cluster (SNC) mode is disabled
+	or enabled respectively) and by RDT event.  Each of these
+	directories has one file per event (e.g. "llc_occupancy",
 	"mbm_total_bytes", and "mbm_local_bytes"). In a MON group these
 	files provide a read out of the current value of the event for
 	all tasks in the group. In CTRL_MON groups these files provide
@@ -478,6 +478,23 @@  if non-contiguous 1s value is supported. On a system with a 20-bit mask
 each bit represents 5% of the capacity of the cache. You could partition
 the cache into four equal parts with masks: 0x1f, 0x3e0, 0x7c00, 0xf8000.
 
+Notes on Sub-NUMA Cluster mode
+==============================
+When SNC mode is enabled Linux may load balance tasks between Sub-NUMA
+nodes much more readily than between regular NUMA nodes since the CPUs
+on Sub-NUMA nodes share the same L3 cache and the system may report
+the NUMA distance between Sub-NUMA nodes with a lower value than used
+for regular NUMA nodes.  Users who do not bind tasks to the CPUs of a
+specific Sub-NUMA node must read the "llc_occupancy", "mbm_total_bytes",
+and "mbm_local_bytes" for all Sub-NUMA nodes where the tasks may execute
+to get the full view of traffic for which the tasks were the source.
+
+The cache allocation feature still provides the same number of
+bits in a mask to control allocation into the L3 cache, but each
+of those ways has its capacity reduced because the cache is divided
+between the SNC nodes. The values reported in the resctrl
+"size" files are adjusted accordingly.
+
 Memory bandwidth Allocation and monitoring
 ==========================================