Re: [PATCH v4 4/9] cxl/region: Calculate peer distance only for reused targets

[Alison Schofield <alison.schofield@intel.com>]

On Mon, Oct 19, 2026 at 03:31:29PM +0800, Richard Cheng wrote:
> On Sat, Oct 17, 2026 at 12:19:49PM +0800, Alison Schofield wrote:
> > From: Richard Cheng <icheng@nvidia.com>
> > 
> > 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.

With cxl_test, the x8 region in cxl-region-sysfs.sh reduces calls to
cxl_port_peer_distance() from 10 to 4, and the x2 auto region from 2
to 1. A misordered-endpoint test confirms that peer validation still
rejects mismatched peers.


> > 
> > Signed-off-by: Richard Cheng <icheng@nvidia.com>
> > Tested-by: Alison Schofield <alison.schofield@intel.com>
> > Signed-off-by: Alison Schofield <alison.schofield@intel.com>
> 
> Hi Alison,
> 
> Really appreciate for the testing and if we can, can we add the testing result
> in the commit message demonstrate benefit it can bring us ?

Added the above for v5, taken from:
https://lore.kernel.org/linux-cxl/atLBlibv3kbT7xv5@aschofie-mobl2.lan/) 

Let me know if you want something else.

-- Alison

> 
> 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 4ab5a1d025a9..8bfebe3e1025 100644
> > --- a/drivers/cxl/core/region.c
> > +++ b/drivers/cxl/core/region.c
> > @@ -1485,10 +1485,10 @@ static int cxl_switch_port_setup_targets(struct cxl_switch_decoder *cxlsd,
> >  	}
> >  
> >  	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)
> > -- 
> > 2.37.3
> >