[v15,16/19] cxl: Compute the entire CXL path latency and bandwidth data

Commit Message

Dave Jiang Dec. 21, 2023, 10:04 p.m. UTC

CXL Memory Device SW Guide [1] rev1.0 2.11.2 provides instruction on how to
calculate latency and bandwidth for CXL memory device. Calculate minimum
bandwidth and total latency for the path from the CXL device to the root
port. The QTG id is retrieved by providing the performance data as input
and calling the root port callback ->get_qos_class(). The retrieved id is
stored with the cxl_port of the CXL device.

For example for a device that is directly attached to a host bus:
Total Latency = Device Latency (from CDAT) + Dev to Host Bus (HB) Link
		Latency + Generic Port Latency
Min Bandwidth = Min bandwidth for link bandwidth between HB
		and CXL device, device CDAT bandwidth, and Generic Port
		Bandwidth

For a device that has a switch in between host bus and CXL device:
Total Latency = Device (CDAT) Latency + Dev to Switch Link Latency +
		Switch (CDAT) Latency + Switch to HB Link Latency +
		Generic Port Latency
Min Bandwidth = Min bandwidth for link bandwidth between CXL device
		to CXL switch, CXL device CDAT bandwidth, CXL switch CDAT
		bandwidth, CXL switch to HB bandwidth, and Generic Port
		Bandwidth.

[1]: https://cdrdv2-public.intel.com/643805/643805_CXL%20Memory%20Device%20SW%20Guide_Rev1p0.pdf

Reviewed-by: Jonathan Cameron <[e-mail]>
Signed-off-by: Dave Jiang <[e-mail]>
---
 drivers/cxl/core/cdat.c |   59 ++++++++++++++++++++++++++++++++++++++++++++++-
 1 file changed, 58 insertions(+), 1 deletion(-)

Patch

diff --git a/drivers/cxl/core/cdat.c b/drivers/cxl/core/cdat.c
index b3ab47d250e1..43dfef80fb84 100644
--- a/drivers/cxl/core/cdat.c
+++ b/drivers/cxl/core/cdat.c
@@ -12,6 +12,9 @@  struct dsmas_entry {
 	struct range dpa_range;
 	u8 handle;
 	struct access_coordinate coord;
+
+	int entries;
+	int qos_class;
 };
 
 static int cdat_dsmas_handler(union acpi_subtable_headers *header, void *arg,
@@ -154,6 +157,55 @@  static int cxl_cdat_endpoint_process(struct cxl_port *port,
 	return cdat_table_parse_output(rc);
 }
 
+static int cxl_port_perf_data_calculate(struct cxl_port *port,
+					struct xarray *dsmas_xa)
+{
+	struct access_coordinate c;
+	struct cxl_port *root_port;
+	struct cxl_root *cxl_root;
+	struct dsmas_entry *dent;
+	int valid_entries = 0;
+	unsigned long index;
+	int rc;
+
+	rc = cxl_endpoint_get_perf_coordinates(port, &c);
+	if (rc) {
+		dev_dbg(&port->dev, "Failed to retrieve perf coordinates.\n");
+		return rc;
+	}
+
+	root_port = find_cxl_root(port);
+	cxl_root = to_cxl_root(root_port);
+	if (!cxl_root->ops || !cxl_root->ops->qos_class)
+		return -EOPNOTSUPP;
+
+	xa_for_each(dsmas_xa, index, dent) {
+		int qos_class;
+
+		dent->coord.read_latency = dent->coord.read_latency +
+					   c.read_latency;
+		dent->coord.write_latency = dent->coord.write_latency +
+					    c.write_latency;
+		dent->coord.read_bandwidth = min_t(int, c.read_bandwidth,
+						   dent->coord.read_bandwidth);
+		dent->coord.write_bandwidth = min_t(int, c.write_bandwidth,
+						    dent->coord.write_bandwidth);
+
+		dent->entries = 1;
+		rc = cxl_root->ops->qos_class(root_port, &dent->coord, 1, &qos_class);
+		if (rc != 1)
+			continue;
+
+		valid_entries++;
+		dent->qos_class = qos_class;
+	}
+
+	if (!valid_entries)
+		return -ENOENT;
+
+	return 0;
+}
+
 static void discard_dsmas(struct xarray *xa)
 {
 	unsigned long index;
@@ -183,7 +235,12 @@  void cxl_endpoint_parse_cdat(struct cxl_port *port)
 		return;
 	}
 
-	/* Performance data processing */
+	rc = cxl_port_perf_data_calculate(port, dsmas_xa);
+	if (rc) {
+		dev_dbg(&port->dev, "Failed to do perf coord calculations.\n");
+		return;
+	}
+
 }
 EXPORT_SYMBOL_NS_GPL(cxl_endpoint_parse_cdat, CXL);