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

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

On 8/20/20 10:42 AM, Denis V. Lunev wrote:
> 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
ping V2