[Libguestfs] [PATCH v2 6/7] v2v: Use unordered writes in qemu-img convert

Without unordered writes, qemu-img read data in parallel, but issue requests in order, keeping only one in-flight request. With unordered writes, qemu keeps up to 8 in-flight requests by default. With this change we see significant improvement in the rhv-upload-plugin. Connection time decreased from 7.08 seconds to 3.77 seconds, 88% faster. Compared with last version using single connection, we are now 42% faster. [connection 1 ops, 3.778596 s] [dispatch 547 ops, 2.977509 s] [write 464 ops, 2.703108 s, 355.62 MiB, 131.56 MiB/s] [zero 81 ops, 0.118312 s, 1.22 GiB, 10.31 GiB/s] [flush 2 ops, 0.000222 s] [connection 1 ops, 3.774985 s] [dispatch 555 ops, 2.976595 s] [write 490 ops, 2.685608 s, 352.19 MiB, 131.14 MiB/s] [zero 63 ops, 0.122802 s, 1.20 GiB, 9.80 GiB/s] [flush 2 ops, 0.000203 s] [connection 1 ops, 3.777071 s] [dispatch 564 ops, 2.930730 s] [write 499 ops, 2.631180 s, 323.38 MiB, 122.90 MiB/s] [zero 63 ops, 0.119163 s, 1.17 GiB, 9.86 GiB/s] [flush 2 ops, 0.000255 s] [connection 1 ops, 3.778360 s] [dispatch 528 ops, 2.979062 s] [write 456 ops, 2.676340 s, 318.00 MiB, 118.82 MiB/s] [zero 70 ops, 0.118221 s, 1.08 GiB, 9.18 GiB/s] [flush 2 ops, 0.000202 s] Signed-off-by: Nir Soffer <nsoffer(a)redhat.com&gt; --- v2v/v2v.ml | 1 + 1 file changed, 1 insertion(+) diff --git a/v2v/v2v.ml b/v2v/v2v.ml index 54f26297..aa9d9713 100644 --- a/v2v/v2v.ml +++ b/v2v/v2v.ml @@ -763,6 +763,7 @@ and copy_targets cmdline targets input output = [ "-n"; "-f"; "qcow2"; "-O"; output#transfer_format t ] @ (if cmdline.compressed then [ "-c" ] else []) @ [ "-S"; "64k" ] @ + [ "-W"; ] @ [ overlay_file; filename ] in let start_time = gettimeofday () in if run_command cmd <> 0 then -- 2.26.2