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Re: [Qemu-block] Change in qemu 2.12 causes qemu-img convert to NBD to w
From: |
Richard W.M. Jones |
Subject: |
Re: [Qemu-block] Change in qemu 2.12 causes qemu-img convert to NBD to write more data |
Date: |
Wed, 7 Nov 2018 15:02:19 +0000 |
User-agent: |
Mutt/1.5.21 (2010-09-15) |
On Wed, Nov 07, 2018 at 04:56:48PM +0200, Nir Soffer wrote:
> Wed, Nov 7, 2018 at 4:36 PM Richard W.M. Jones <address@hidden> wrote:
>
> > Another thing I tried was to change the NBD server (nbdkit) so that it
> > doesn't advertise zero support to the client:
> >
> > $ nbdkit --filter=log --filter=nozero memory size=6G logfile=/tmp/log \
> > --run './qemu-img convert ./fedora-28.img -n $nbd'
> > $ grep '\.\.\.$' /tmp/log | sed 's/.*\([A-Z][a-z]*\).*/\1/' | uniq -c
> > 2154 Write
> >
> > Not surprisingly no zero commands are issued. The size of the write
> > commands is very uneven -- it appears to be send one command per block
> > of zeroes or data.
> >
> > Nir: If we could get information from imageio about whether zeroing is
> > implemented efficiently or not by the backend, we could change
> > virt-v2v / nbdkit to advertise this back to qemu.
> >
>
> There is no way to detect the capability, ioctl(BLKZEROOUT) always
> succeeds, falling back to manual zeroing in the kernel silently
>
> Even if we could, sending zero on the wire from qemu may be even
> slower,
Yes this is a very good point. Sending zeroes would be terrible.
Rich.
--
Richard Jones, Virtualization Group, Red Hat http://people.redhat.com/~rjones
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- [Qemu-block] Change in qemu 2.12 causes qemu-img convert to NBD to write more data, Richard W.M. Jones, 2018/11/07
- Re: [Qemu-block] Change in qemu 2.12 causes qemu-img convert to NBD to write more data, Richard W.M. Jones, 2018/11/07
- Re: [Qemu-block] Change in qemu 2.12 causes qemu-img convert to NBD to write more data, Nir Soffer, 2018/11/07
- Re: [Qemu-block] Change in qemu 2.12 causes qemu-img convert to NBD to write more data,
Richard W.M. Jones <=
- Re: [Qemu-block] Change in qemu 2.12 causes qemu-img convert to NBD to write more data, Kevin Wolf, 2018/11/07
- Re: [Qemu-block] Change in qemu 2.12 causes qemu-img convert to NBD to write more data, Nir Soffer, 2018/11/07
- Re: [Qemu-block] Change in qemu 2.12 causes qemu-img convert to NBD to write more data, Nir Soffer, 2018/11/11
- Re: [Qemu-block] Change in qemu 2.12 causes qemu-img convert to NBD to write more data, Nir Soffer, 2018/11/15
- Re: [Qemu-block] Change in qemu 2.12 causes qemu-img convert to NBD to write more data, Kevin Wolf, 2018/11/16
- Re: [Qemu-block] Change in qemu 2.12 causes qemu-img convert to NBD to write more data, Nir Soffer, 2018/11/17
- Re: [Qemu-block] Change in qemu 2.12 causes qemu-img convert to NBD to write more data, Richard W.M. Jones, 2018/11/17
- Re: [Qemu-block] Change in qemu 2.12 causes qemu-img convert to NBD to write more data, Nir Soffer, 2018/11/18
- Re: [Qemu-block] Change in qemu 2.12 causes qemu-img convert to NBD to write more data, Kevin Wolf, 2018/11/19
Re: [Qemu-block] Change in qemu 2.12 causes qemu-img convert to NBD to write more data, Eric Blake, 2018/11/07