This series reorganizes the locking in virtio-scsi, introducing separate
scatterlists for each target and "pipelining" the locks so that one
command can be queued while the other is prepared. This improves
performance when there are multiple in-flight operations.
For example, a simple "if=/dev/sda of=/dev/null bs=128M iflag=direct"
(the source being a 10G disk, residing entirely in the host buffer cache)
improve as follows. The additional locking does not cause any penalty
with only one dd process, while 2 simultaneous I/O operations improve
their times by 3%:
number of simultaneous dd
1 2
----------------------------------------
current 5.9958s 10.2640s
patched 5.9531s 9.8663s
Times are best of 10, and taken on a 2-VCPU guest.
drivers/scsi/virtio_scsi.c | 226 ++++++++++++++++++++++++++++---------------
1 file changed, 151 insertions(+), 75 deletions(-)
Paolo Bonzini (4):
virtio-scsi: unlock during kick
virtio-scsi: split locking per vq
virtio-scsi: release sg_lock after add_buf
virtio-scsi: split scatterlist per target
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