[PATCH 0/2] virtio-blk: use blk_io_plug_call() instead of notification BH

[Stefan Hajnoczi]

Replace the seldom-used virtio-blk notification BH mechanism with
blk_io_plug(). This is part of an effort to enable the multi-queue block layer
in virtio-blk. The notification BH was not multi-queue friendly.

The blk_io_plug() mechanism improves fio rw=randread bs=4k iodepth=64 numjobs=8
IOPS by ~9% with a single IOThread and 8 vCPUs (this is not even a multi-queue
block layer configuration) compared to no completion batching. iodepth=1
decreases by ~1% but this could be noise. Benchmark details are available here:
https://gitlab.com/stefanha/virt-playbooks/-/tree/blk_io_plug-irqfd

Stefan Hajnoczi (2):
  virtio: use blk_io_plug_call() in virtio_irqfd_notify()
  virtio-blk: remove batch notification BH

 block/io_uring.c                |  6 +++++
 block/linux-aio.c               |  4 +++
 hw/block/dataplane/virtio-blk.c | 48 +--------------------------------
 hw/virtio/virtio.c              | 10 ++++++-
 4 files changed, 20 insertions(+), 48 deletions(-)

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2.41.0