Re: [PATCH v8 0/6] block: seriously improve savevm/loadvm performance

["Denis V. Lunev" <den@openvz.org>]

On 7/9/20 4:26 PM, 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
>
> Changes from v7:
> - dropped lock from LoadVMState
> - fixed assert in last patch
> - dropped patch 1 as queued
>
> Changes from v6:
> - blk_load_vmstate kludges added (patchew problem fixed)
>
> Changes from v5:
> - loadvm optimizations added with Vladimir comments included
>
> Changes from v4:
> - added patch 4 with blk_save_vmstate() cleanup
> - added R-By
> - bdrv_flush_vmstate -> bdrv_finalize_vmstate
> - fixed return code of bdrv_co_do_save_vmstate
> - fixed typos in comments (Eric, thanks!)
> - fixed patchew warnings
>
> Changes from v3:
> - rebased to master
> - added patch 3 which removes aio_task_pool_wait_one()
> - added R-By to patch 1
> - patch 4 is rewritten via bdrv_run_co
> - error path in blk_save_vmstate() is rewritten to call bdrv_flush_vmstate
>   unconditionally
> - added some comments
> - fixes initialization in bdrv_co_vmstate_save_task_entry as suggested
>
> Changes from v2:
> - code moved from QCOW2 level to generic block level
> - created bdrv_flush_vmstate helper to fix 022, 029 tests
> - added recursive for bs->file in bdrv_co_flush_vmstate (fix 267)
> - fixed blk_save_vmstate helper
> - fixed coroutine wait as Vladimir suggested with waiting fixes from me
>
> Changes from v1:
> - patchew warning fixed
> - fixed validation that only 1 waiter is allowed in patch 1
>
> Signed-off-by: Denis V. Lunev <den@openvz.org>
> CC: Kevin Wolf <kwolf@redhat.com>
> CC: Max Reitz <mreitz@redhat.com>
> CC: Stefan Hajnoczi <stefanha@redhat.com>
> CC: Fam Zheng <fam@euphon.net>
> CC: Juan Quintela <quintela@redhat.com>
> CC: "Dr. David Alan Gilbert" <dgilbert@redhat.com>
> CC: Vladimir Sementsov-Ogievskiy <vsementsov@virtuozzo.com>
> CC: Denis Plotnikov <dplotnikov@virtuozzo.com>
>
>
ping