On Wed, Jan 29, 2025 at 09:23:37AM -0500, Martin K. Petersen wrote: > Doing a verification pass in the write hot path had a substantial > performance impact when I originally did this. Oh yes, it absolutely will. While the CRC implementations got a lot faster in the last years, there's still a cost. It also touches a lot of cache lines. > Even remapping the ref > tag has an impact on cache. That's why DIX1.1 moved ref tag remapping to > the HBA so we could avoid touching the PI buffer altogether in the hot > path. As in supplying an offset for the ref tag somewhere in the HBA specific per-command payload? That's not implemented in Linux as far as I can tell, or did I miss something? > > I.e. if userspace passes incorrect information it can trigger a > > command failure and thus the driver error handler, which is something > > we don't usually allow for "regular" I/O. > > Do you trigger EH in NVMe? For SCSI we just bubble the PI error up > without retrying. We don't have the EH thread from hell, but there is error handling yes.