Hi Tony,
How does user know Sub-NUMA Cluster mode is being enabled on the system?
Do you have any information in /sys/fs/resctrl/info?
Below documentation does not have any info about it.
Would it be better to add that in "info" directory?
Thanks
Babu
On 8/29/23 18:44, 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 <[email protected]>
> ---
> Documentation/arch/x86/resctrl.rst | 25 ++++++++++++++++++++++---
> 1 file changed, 22 insertions(+), 3 deletions(-)
>
> diff --git a/Documentation/arch/x86/resctrl.rst b/Documentation/arch/x86/resctrl.rst
> index cb05d90111b4..407764f43f25 100644
> --- a/Documentation/arch/x86/resctrl.rst
> +++ b/Documentation/arch/x86/resctrl.rst
> @@ -345,9 +345,15 @@ 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
> + 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. E.g. on a system with
> + SNC mode disabled with two L3 domains there will be subdirectories
> + "mon_L3_00" and "mon_L3_01". The numerical suffix refers to the
> + L3 cache id. With SNC enabled the directory names are the same,
> + but the numerical suffix refers to the node id.
> + Mappings from node ids to CPUs are available in the
> + /sys/devices/system/node/node*/cpulist files. Each of these
> directories have 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
> @@ -452,6 +458,19 @@ and 0xA are not. 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 the "llc_occupancy", "mbm_total_bytes", and
> +"mbm_local_bytes" will only give accurate results for well behaved NUMA
> +applications. I.e. those that perform the majority of memory accesses
> +to memory on the local NUMA node to the CPU where the task is executing.
> +
> +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
> ==========================================
>
--
Thanks
Babu Moger
> How does user know Sub-NUMA Cluster mode is being enabled on the system?
>
> Do you have any information in /sys/fs/resctrl/info?
>
> Below documentation does not have any info about it.
> Would it be better to add that in "info" directory?
Babu,
My original patch series added an "snc_ways" file to the info/ directory
to make this visible. But I was talked out of it because of a lack of clear
user mode use case that needs it.
https://lore.kernel.org/all/[email protected]/
Users can figure out whether SNC is enabled by looking at topology
files for nodes and L3 caches in /sys. The open question is whether
we should provide a simple short cut to that information, or make them
walk two miles uphill in the snow to figure it out.
-Tony
On 9/26/23 14:11, Luck, Tony wrote:
>> How does user know Sub-NUMA Cluster mode is being enabled on the system?
>>
>> Do you have any information in /sys/fs/resctrl/info?
>>
>> Below documentation does not have any info about it.
>> Would it be better to add that in "info" directory?
>
>
> Babu,
>
> My original patch series added an "snc_ways" file to the info/ directory
> to make this visible. But I was talked out of it because of a lack of clear
> user mode use case that needs it.
ok. Lets go with it.
Thanks
Babu Moger