[RFC PATCH] cxl/region: Calculate peer distance only for reused targets

[RFC PATCH] cxl/region: Calculate peer distance only for reused targets

[Richard Cheng]

This patch depends on Alison Schofield's v3 "cxl/region: Refactor
cxl_port_setup_targets()" series [1], this is inspired from that serie
as well, since her serie contains no functional change, I pull this one
out as a standalone patch.

cxl_switch_port_setup_targets() calculates peer distance before
searching the existing targets. When the endpoint needs a new target,
the calculated distance is never used.

Move cxl_port_peer_distance() into the matching-target branch,
immediately before check_last_peer(). This avoids unnecessary ancestor
walks and per-port region lookups when adding distinct targets.

[1]:
https://lore.kernel.org/linux-cxl/cover.1791860305.git.alison.schofield@intel.com/
Signed-off-by: Richard Cheng <icheng@nvidia.com>
---
I don't have available HW for multi-way interleaving setup, so I can't
exercise the case optimized here. I would appreciate if someone is
williing to validate the actual benefit of this.

Best regards,
Richard Cheng.
---
 drivers/cxl/core/region.c | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/drivers/cxl/core/region.c b/drivers/cxl/core/region.c
index 50f4830c225d..efd173c57dad 100644
--- a/drivers/cxl/core/region.c
+++ b/drivers/cxl/core/region.c
@@ -1666,10 +1666,10 @@ static int cxl_switch_port_setup_targets(struct cxl_port *port, struct cxl_regio
 
 	cxlsd = to_cxl_switch_decoder(&cxld->dev);
 	if (cxl_rr->nr_targets_set) {
-		int distance = cxl_port_peer_distance(port, cxlr);
-
 		for (int i = 0; i < cxl_rr->nr_targets_set; i++)
 			if (ep->dport == cxlsd->target[i]) {
+				int distance = cxl_port_peer_distance(port, cxlr);
+
 				rc = check_last_peer(cxled, ep, cxl_rr,
 						     distance);
 				if (rc)
-- 
2.43.0