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Re: [Qemu-devel] Effect of qemu-img convert -m and -W options
From: |
Stefan Hajnoczi |
Subject: |
Re: [Qemu-devel] Effect of qemu-img convert -m and -W options |
Date: |
Mon, 20 Nov 2017 15:57:51 +0000 |
User-agent: |
Mutt/1.9.1 (2017-09-22) |
On Thu, Nov 16, 2017 at 06:00:54PM +0000, Richard W.M. Jones wrote:
> On Thu, Nov 16, 2017 at 05:30:48PM +0000, Stefan Hajnoczi wrote:
> > On Thu, Nov 16, 2017 at 3:10 PM, Richard W.M. Jones <address@hidden> wrote:
> > > Both local filesystems, but on different SATA devices.
> >
> > Okay. I'm curious what the strace -f output looks like (only the
> > preadv(2)/pwritev(2) syscalls are interesting at the moment).
>
> Here's the full strace from one run:
>
> http://oirase.annexia.org/tmp/strace.xz
>
> The command is (with the output.qcow2 file created in a previous run):
>
> $ strace -o /tmp/strace -f -s 1024 qemu-img convert -f raw fedora-27.img -O
> qcow2 /var/tmp/output.qcow2 -m 8 -W -n
>
> The version of qemu is: qemu-2.10.0-7.fc28.x86_64
Requests are being handled in parallel and the exact order is random due
to I/O completion times and thread scheduling.
I didn't see an obvious pattern to optimize but only spent a little time
studying the strace.
Stefan
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