Hi Suganath, > Theoretically we want to use h/w capability (to translate IEEE to PRP) > for smaller IO size to leverage h/w capability. Nobody says we have to use the capability just because the hardware has it. Unlike some other operating systems, Linux will only submit I/Os to the driver that conform to the reported underlying constraints of the hardware. I fail to understand how letting the HBA firmware translate an SGL to a PRP for a subset of I/Os could do anything but add latency. Plus complexity in the hot path of the driver. > - If the unmap translation in firmware is slow, why don't you translate > WRITE SAME/w UNMAP set to DSM DEALLOCATE without requiring > applications to do encapsulated passthrough? > => As of now, current FW supports UNMAP command but not WRITE_SAME for > NVME drive. We did some experiment to convert UMAP command in driver, > but that is not really giving any performance improvement. It is imperative that the common use case, Linux' discard infrastructure, is working correctly and is as performant as any application-driven passthrough workaround. Unlike SCSI-to-SATA translation you have the benefit of a 1:1 mapping between UNMAP and DEALLOCATE. I'm not even sure why there would be a significant performance penalty in the firmware? > We would like to continue with UNMAP (and all other non-read/write > commands) to be handled in FW. And yet patch 4 circumvents that statement by adding support for encapsulated commands to bypass the FW translation... -- Martin K. Petersen Oracle Linux Engineering
