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Re: [PATCH v8 0/6] block: seriously improve savevm/loadvm performance
From: |
Stefan Hajnoczi |
Subject: |
Re: [PATCH v8 0/6] block: seriously improve savevm/loadvm performance |
Date: |
Mon, 14 Sep 2020 14:13:04 +0100 |
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
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