RE: [PATCH v3 2/3] cxl/region: Add sysfs attribute for locality attributes of CXL regions

[Dan Williams <dan.j.williams@intel.com>]

Dave Jiang wrote:
> Add read/write latencies and bandwidth sysfs attributes for the enabled CXL
> region. The bandwidth is the aggregated bandwidth of all devices that
> contribute to the CXL region. The latency is the worst latency of the
> device amongst all the devices that contribute to the CXL region.
> 
> Signed-off-by: Dave Jiang <dave.jiang@intel.com>
> ---
> v3:
> - Make attribs not visible if no data (Jonathan)
> - Check against coord.attrib (Jonathan)
> - Fix documentation verbiage (Jonathan)
> ---
>  Documentation/ABI/testing/sysfs-bus-cxl |   60 +++++++++++++++++++++++++++++++
>  drivers/cxl/core/region.c               |   40 +++++++++++++++++++++
>  2 files changed, 100 insertions(+)
> 
> diff --git a/Documentation/ABI/testing/sysfs-bus-cxl b/Documentation/ABI/testing/sysfs-bus-cxl
> index fff2581b8033..86d3dbe12129 100644
> --- a/Documentation/ABI/testing/sysfs-bus-cxl
> +++ b/Documentation/ABI/testing/sysfs-bus-cxl
> @@ -552,3 +552,63 @@ Description:
>  		attribute is only visible for devices supporting the
>  		capability. The retrieved errors are logged as kernel
>  		events when cxl_poison event tracing is enabled.
> +
> +
> +What:		/sys/bus/cxl/devices/regionZ/read_bandwidth
> +Date:		Jan, 2024
> +KernelVersion:	v6.9
> +Contact:	linux-cxl@vger.kernel.org
> +Description:
> +		(RO) The aggregated read bandwidth of the region. The number is
> +		the accumulated read bandwidth of all CXL memory devices that
> +		contributes to the region in MB/s. Should be equivalent to

Perhaps:

s|Should be equivalent|It the identical data that would appear in
/sys/devices/system/node/nodeX/access0/initiators/read_bandwidth if /
when this region is onlined as memory nodeX|.

Note that I did a s/accessY/access0/ since this data is relative to a
single Generic Port. The performance from other intiators that go
through an alternate port is not represented, right?

> +		attributes in
> +		/sys/devices/system/node/nodeX/accessY/initiators/read_bandwidth.
> +		See Documentation/ABI/stable/sysfs-devices-node. The generic
> +		target bandwidth that is part of the whole path calculation is
> +		the best performance latency provided by the HMAT SSLBIS table.

Shouldn't this be s/HMAT SSBLIS/CDAT DSBLIS/ throughout?

...but maybe just delete it because this number is pretty far removed
from the CDAT data. The data has been munged by considering the
intervening topology, and is aggregated across all the endpoints.