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 <rjo...@redhat.com> > > 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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