On Thu, Jul 09, 2020 at 04:26:38PM +0300, Denis V. Lunev wrote:
> This series do standard basic things:
> - it creates intermediate buffer for all writes from QEMU migration code
>   to QCOW2 image,
> - this buffer is sent to disk asynchronously, allowing several writes to
>   run in parallel.
> 
> In general, migration code is fantastically inefficent (by observation),
> buffers are not aligned and sent with arbitrary pieces, a lot of time
> less than 100 bytes at a chunk, which results in read-modify-write
> operations with non-cached operations. It should also be noted that all
> operations are performed into unallocated image blocks, which also suffer
> due to partial writes to such new clusters.
> 
> This patch series is an implementation of idea discussed in the RFC
> posted by Denis Plotnikov
> https://lists.gnu.org/archive/html/qemu-devel/2020-04/msg01925.html
> Results with this series over NVME are better than original code
>                 original     rfc    this
> cached:          1.79s      2.38s   1.27s
> non-cached:      3.29s      1.31s   0.81s

Kevin and Max: Is this going through one of your trees?

Stefan