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The raw-posix block driver implements Linux AIO batching so multiple requests can be submitted with a single io_submit(2) system call. Batching is currently only used by virtio-scsi and virtio-blk-data-plane. Enable batching for regular virtio-blk so the number of io_submit(2) system calls is reduced for workloads with queue depth > 1. In 4KB random read performance tests with queue depth 32, the CPU utilization on the host is reduced by 9.4%. The fio job is as follows: [global] bs=4k ioengine=libaio iodepth=32 direct=1 sync=0 time_based=1 runtime=30 clocksource=gettimeofday ramp_time=5 [job1] rw=randread filename=/dev/vdb size=4096M write_bw_log=fio write_iops_log=fio write_lat_log=fio log_avg_msec=1000 This benchmark was run on an raw image on LVM. The disk was an SSD drive and -drive cache=none,aio=native was used. Tested-by: Pradeep Surisetty <psuriset@redhat.com> Signed-off-by: Stefan Hajnoczi <stefanha@redhat.com> Reviewed-by: Fam Zheng <famz@redhat.com>
Read the documentation in qemu-doc.html or on http://wiki.qemu-project.org - QEMU team