Hi all! Here is a filter, which does preallocation on write.
In Virtuozzo we have to deal with some custom distributed storage solution, where allocation is relatively expensive operation. We have to workaround it in Qemu, so here is a new filter. Performance results with the following test are very significant: IMG=/megassd/z; FILE_OPTS=file.filename=$IMG; COUNT=15000; CHUNK=64K; \ CLUSTER=1M; rm -f $IMG; \ ./qemu-img create -f qcow2 -o cluster_size=$CLUSTER $IMG 1G; \ ./qemu-img bench -c $COUNT -d 1 -s $CHUNK -w -t none --image-opts driver=qcow2,$FILE_OPTS; - qemu-img bench reports ~44.3s, and if I switch FILE_OPTS to be FILE_OPTS=file.driver=preallocate,file.file.filename=$IMG qemu-img bench reports ~4.3s, 90% benefit! (/megassd is a mount point of distributed storage) Unfortunately, I don't know another real-world case where preallocation would so helpful. If someone have running ceph instance and can check it I'd be very grateful. Still, I hope, it may be useful at least for some testing purposes. And, small example I have: small writes with small sectors on usual ext4 over ssd gives the following for me: IMG=/ssd/z; FILE_OPTS=file.filename=$IMG; COUNT=15000; CHUNK=512; \ CLUSTER=512; rm -f $IMG; \ ./qemu-img create -f qcow2 -o cluster_size=$CLUSTER $IMG 1G; \ ./qemu-img bench -c $COUNT -d 1 -s $CHUNK -w -t none --image-opts driver=qcow2,$FILE_OPTS; ~17.1s and, if I switch FILE_OPTS to use new filter, the result is ~14.9s, i.e ~13% better. ===== The series also introduces bdrv-lock-region interface, which may be reused to implement copy-on-read operation directly inside copy-on-read filter, instead of handling the special flag in generic code. Vladimir Sementsov-Ogievskiy (5): block/io: introduce bdrv_try_mark_request_serialising block/io: introduce bdrv_co_range_try_lock block: introduce preallocate filter iotests: QemuIoInteractive: use qemu_io_args_no_fmt iotests: add 298 to test new preallocate filter driver qapi/block-core.json | 3 +- include/block/block.h | 9 ++ include/block/block_int.h | 16 +++ include/qemu/typedefs.h | 1 + block/io.c | 142 ++++++++++++++++--- block/preallocate.c | 255 ++++++++++++++++++++++++++++++++++ block/Makefile.objs | 1 + tests/qemu-iotests/298 | 45 ++++++ tests/qemu-iotests/298.out | 5 + tests/qemu-iotests/group | 1 + tests/qemu-iotests/iotests.py | 2 +- 11 files changed, 455 insertions(+), 25 deletions(-) create mode 100644 block/preallocate.c create mode 100644 tests/qemu-iotests/298 create mode 100644 tests/qemu-iotests/298.out -- 2.18.0