[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index]
Re: [PATCH v3 0/8] blockdev: avoid acquiring AioContext lock twice at do
From: |
Kevin Wolf |
Subject: |
Re: [PATCH v3 0/8] blockdev: avoid acquiring AioContext lock twice at do_drive_backup and do_blockdev_backup |
Date: |
Tue, 19 Nov 2019 12:18:40 +0100 |
User-agent: |
Mutt/1.12.1 (2019-06-15) |
Am 19.11.2019 um 11:54 hat Sergio Lopez geschrieben:
>
> Max Reitz <address@hidden> writes:
>
> > On 13.11.19 14:24, Sergio Lopez wrote:
> >>
> >> Sergio Lopez <address@hidden> writes:
> >>
> >>> address@hidden writes:
> >>>
> >>>> Patchew URL: https://patchew.org/QEMU/address@hidden/
> >>>>
> >>>>
> >>>>
> >>>> Hi,
> >>>>
> >>>> This series failed the docker-quick@centos7 build test. Please find the
> >>>> testing commands and
> >>>> their output below. If you have Docker installed, you can probably
> >>>> reproduce it
> >>>> locally.
> >>>>
> >>>> === TEST SCRIPT BEGIN ===
> >>>> #!/bin/bash
> >>>> make docker-image-centos7 V=1 NETWORK=1
> >>>> time make docker-test-quick@centos7 SHOW_ENV=1 J=14 NETWORK=1
> >>>> === TEST SCRIPT END ===
> >>>>
> >>>> TEST iotest-qcow2: 268
> >>>> Failures: 141
> >>>
> >>> Hm... 141 didn't fail in my test machine. I'm going to have a look.
> >>
> >> So here's the output:
> >>
> >> --- /root/qemu/tests/qemu-iotests/141.out 2019-11-12 04:43:27.651557587
> >> -0500
> >> +++ /root/qemu/build/tests/qemu-iotests/141.out.bad 2019-11-13
> >> 08:12:06.575967337 -0500
> >> @@ -10,6 +10,8 @@
> >> Formatting 'TEST_DIR/o.IMGFMT', fmt=IMGFMT size=1048576
> >> backing_file=TEST_DIR/t.IMGFMT backing_fmt=IMGFMT
> >> {"timestamp": {"seconds": TIMESTAMP, "microseconds": TIMESTAMP},
> >> "event": "JOB_STATUS_CHANGE", "data": {"status": "created", "id": "job0"}}
> >> {"timestamp": {"seconds": TIMESTAMP, "microseconds": TIMESTAMP},
> >> "event": "JOB_STATUS_CHANGE", "data": {"status": "running", "id": "job0"}}
> >> +{"timestamp": {"seconds": TIMESTAMP, "microseconds": TIMESTAMP},
> >> "event": "JOB_STATUS_CHANGE", "data": {"status": "paused", "id": "job0"}}
> >> +{"timestamp": {"seconds": TIMESTAMP, "microseconds": TIMESTAMP},
> >> "event": "JOB_STATUS_CHANGE", "data": {"status": "running", "id": "job0"}}
> >> {"error": {"class": "GenericError", "desc": "Node 'drv0' is busy: node is
> >> used as backing hd of 'NODE_NAME'"}}
> >> {"return": {}}
> >> {"timestamp": {"seconds": TIMESTAMP, "microseconds": TIMESTAMP},
> >> "event": "JOB_STATUS_CHANGE", "data": {"status": "aborting", "id": "job0"}}
> >>
> >> Those extra lines, the "paused" and "running", are a result of the job
> >> being done in a transaction, within a drained section.
> >>
> >> We can update 141.out, but now I'm wondering, was it safe creating the
> >> job at do_drive_backup() outside of a drained section, as
> >> qmp_drive_backup was doing?
> >
> > I think it is. Someone needs to drain the source node before attaching
> > the job filter (which intercepts writes), and bdrv_backup_top_append()
> > does precisely this.
> >
> > If the source node is in an I/O thread, you could argue that the drain
> > starts later than when the user has invoked the backup command, and so
> > some writes might slip through. That’s correct. But at the same time,
> > it’s impossible to drain it the instant the command is received. So
> > some writes might always slip through (and the drain will not stop them
> > either, it will just let them happen).
> >
> > Therefore, I think it’s fine the way it is.
> >
> >> Do you think there may be any potential drawbacks as a result of always
> >> doing it now inside a drained section?
> >
> > Well, one drawback is clearly visible. The job goes to paused for no
> > reason.
>
> This is something that already happens when requesting the drive-backup
> through a transaction:
>
> {"execute":"transaction","arguments":{"actions":[{"type":"drive-backup","data":{"device":"drv0","target":"o.qcow2","sync":"full","format":"qcow2"}}]}}
>
> I don't think it makes sense to have two different behaviors for the
> same action. So we either accept the additional pause+resume iteration
> for qmp_drive_backup, or we remove the drained section from the
> transaction based one.
>
> What do you think?
Draining all involved nodes is necessary for transactions, because you
want a consistent backup across all involved disks. That is, you want it
to be a snapshot at the same point in time for all of them - no requests
may happen between starting backup on the first and the second disk.
For a single device operation, this requirement doesn't exist, because
there is nothing else that must happen at the same point in time.
Kevin
signature.asc
Description: PGP signature
- [PATCH v3 8/8] blockdev: honor bdrv_try_set_aio_context() context requirements, (continued)
- [PATCH v3 8/8] blockdev: honor bdrv_try_set_aio_context() context requirements, Sergio Lopez, 2019/11/12
- [PATCH v3 6/8] blockdev: place blockdev_backup_prepare with the other related transaction helpers, Sergio Lopez, 2019/11/12
- [PATCH v3 3/8] blockdev: place drive_backup_prepare with the other related transaction functions, Sergio Lopez, 2019/11/12
- [PATCH v3 7/8] blockdev: change qmp_blockdev_backup to make use of transactions, Sergio Lopez, 2019/11/12
- [PATCH v3 5/8] blockdev: merge blockdev_backup_prepare with do_blockdev_backup, Sergio Lopez, 2019/11/12
- Re: [PATCH v3 0/8] blockdev: avoid acquiring AioContext lock twice at do_drive_backup and do_blockdev_backup, no-reply, 2019/11/12
- Re: [PATCH v3 0/8] blockdev: avoid acquiring AioContext lock twice at do_drive_backup and do_blockdev_backup, Sergio Lopez, 2019/11/13
- Re: [PATCH v3 0/8] blockdev: avoid acquiring AioContext lock twice at do_drive_backup and do_blockdev_backup, Sergio Lopez, 2019/11/13
- Re: [PATCH v3 0/8] blockdev: avoid acquiring AioContext lock twice at do_drive_backup and do_blockdev_backup, Max Reitz, 2019/11/19
- Re: [PATCH v3 0/8] blockdev: avoid acquiring AioContext lock twice at do_drive_backup and do_blockdev_backup, Sergio Lopez, 2019/11/19
- Re: [PATCH v3 0/8] blockdev: avoid acquiring AioContext lock twice at do_drive_backup and do_blockdev_backup,
Kevin Wolf <=
- Re: [PATCH v3 0/8] blockdev: avoid acquiring AioContext lock twice at do_drive_backup and do_blockdev_backup, Sergio Lopez, 2019/11/19
- Re: [PATCH v3 0/8] blockdev: avoid acquiring AioContext lock twice at do_drive_backup and do_blockdev_backup, Kevin Wolf, 2019/11/19
- Re: [PATCH v3 0/8] blockdev: avoid acquiring AioContext lock twice at do_drive_backup and do_blockdev_backup, Sergio Lopez, 2019/11/19