[Qemu-devel] [PATCH 0/9] Add full scatter-gather support for SCSI generic devices

[Alex Pyrgiotis]

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.

Cheers,
Alex

Alex Pyrgiotis (9):
  dma-helpers: Expose the sg mapping logic
  dma-helpers: Add support for ioctl operations
  dma-helpers: Do not truncate small qiovs
  scsi-generic: Add common functions
  scsi-generic: Separate `sg_io_hdr' initializations
  scsi-generic: Make request execution buf-specific
  scsi-generic: Make data-copying logic clearer
  scsi-generic: Factor out response interception
  scsi-generic: Allow full scatter-gather support

 dma-helpers.c          | 184 ++++++++++++++++++---
 hw/scsi/scsi-generic.c | 422 +++++++++++++++++++++++++++++++++++++------------
 include/sysemu/dma.h   |   8 +
 trace-events           |   4 +-
 4 files changed, 488 insertions(+), 130 deletions(-)

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2.6.2