On Fri, Oct 23, 2026 at 03:15:31PM -0500, Bjorn Helgaas wrote: > On Fri, Oct 23, 2026 at 04:00:36PM -0300, Jason Gunthorpe wrote: > > On Fri, Oct 23, 2026 at 01:27:15PM -0500, Bjorn Helgaas wrote: > > > > > > Yes, the ACS combination is selected to avoid ordering issues > > > > > > Does a user have any way to know whether the configuration is safe? > > > > No, unfortunately in PCIe so much is really difficult when it comes to > > deployment :( > > > > > I'm wondering whether users might use "pci=config_acs=" to configure > > > ACS so things appear to work as they prefer but may not provide the > > > ordering guarantees drivers depend on. > > > > I imagine that could happen, but on most practical systems the root > > complex will blow up if you do asymmetric routing so there is an early > > indication. > > > > I know this because I've help debug such configurations at > > customers. Some servers helpfully MCE if you do this. Lovely. > > I'm still confused about this because earlier in this thread, I > thought Leon said you do asymmetric routing: > > Bjorn> And I guess asymmetric fabrics must mean fabrics where > Bjorn> Request Redirect and Completion Redirect are not set the same > Bjorn> way? > > Leon> Yes, in some of our systems, deviceA to deviceB is going > Leon> through different route than deviceB to deviceA.
Yeah, that's what I clarifed, it isn't quite accurate. The asymetric routing is between Strict Order and Relaxed Order TLPs, not request/response. Jason
