[Qemu-devel] [PATCH V2 0/4] *virtio-blk: add multiread support

[Peter Lieven <pl@kamp.de>]

this series adds the long missing multiread support to virtio-blk.

some remarks:
 - i introduced rd_merged and wr_merged block accounting stats to
   blockstats as a generic interface which can be set from any
   driver that will introduce multirequest merging in the future.
 - the knob to disable request merging is not yet there. I would
   add it to the device properties also as a generic interface
   to have the same switch for any driver that might introduce
   request merging in the future. As there has been no knob in
   the past I would post this as a seperate series as it needs
   some mangling in parameter parsing which might lead to further
   discussions.
 - the old multiwrite interface is still there and might be removed.

v1->v2:
 - add overflow checking for nb_sectors [Kevin]
 - do not change the name of the macro of max mergable requests. [Fam]

RFC v2->v1:
 - added Erics grammar corrections to Patch 4
 - Patch 4
  - reworked the IF tree to a SWITCH statement to make it easier
    to understand in virtio_blk_handle_request
  - stop merging if requests switch from read to write or vice
    versa. e..g, otherwise we could introduce big delays as a small
    read request could be followed by a lot of write requests
    and the read requests sits there until the queue is empty.

RFC v1->RFC v2:
 - completed Patch 1 by the example in qmp-commands.hx [Eric]
 - used bool for merge in Patch 4 [Max]
 - fixed a few typos in the commit msg of Patch 4 [Max]
 - do not start merging and directly pass req[0]->qiov in case of num_reqs == 1
 - avoid allocating memory for the multireq [Kevin]
 - do not import block_int.h and add appropiate iface to block-backend [Kevin]
 - removed debug output and added trace event for multireq [Kevin]
 - fixed alloc hint for the merge qiov [Kevin]
 - currently did not split virtio_submit_multireq into rw code since
   the redundant code would now be much bigger part than in the original patch.
 - added a merge_qiov to VirtioBlockRequest. Abusing the qiov was not possible
   because it is initialized externally with guest memory [Kevin]
 - added a pointer to VirtioBlockRequest to create a linked list
   of VirtioBlockBlockRequests. This list is used to complete all
   requests belonging to a multireq [Kevin]

Peter Lieven (4):
  block: add accounting for merged requests
  hw/virtio-blk: add a constant for max number of merged requests
  block-backend: expose bs->bl.max_transfer_length
  virtio-blk: introduce multiread

 block.c                         |    2 +
 block/accounting.c              |    7 ++
 block/block-backend.c           |    5 +
 block/qapi.c                    |    2 +
 hmp.c                           |    6 +-
 hw/block/dataplane/virtio-blk.c |    6 +-
 hw/block/virtio-blk.c           |  242 ++++++++++++++++++++++++---------------
 include/block/accounting.h      |    3 +
 include/hw/virtio/virtio-blk.h  |   20 +++-
 include/sysemu/block-backend.h  |    1 +
 qapi/block-core.json            |    9 +-
 qmp-commands.hx                 |   22 +++-
 trace-events                    |    1 +
 13 files changed, 216 insertions(+), 110 deletions(-)

-- 
1.7.9.5