On 16/12/2015 17:55, Alex Pyrgiotis wrote: > Hi all, > > This patch is an attempt to boost the performance of "scsi-generic" and > "scsi-block" device types, by removing an extra data copy and reducing > their memory footprint. More specifically, the problem lies in the > functions in the `scsi-generic_req_ops` struct of scsi-generic.c. These > functions rely on an intermediate buffer to do the SG_IO ioctl request, > without checking if the SCSI controller has provided a scatter-gather > list with the request. > > In a nutshell, our proposal is to map the provided scatter-gather list > (if any) to the address space of the QEMU process and use the resulting > iovec as the buffer for the ioctl request. You'll find that the logic is > quite similar to the one used in scsi-disk.c.
Which commands have large payloads and are on the data path, for scsi-block? Or is the use case just scsi-generic (e.g. tape devices?)? (Just trying to understand before I dive into the patches). Paolo
