Re: [uml-devel] [PATCH] um: ubd: Add REQ_FLUSH suppport

["Richard W.M. Jones" <rjones@redhat.com>]

On Mon, Aug 19, 2013 at 12:13:14PM +0200, Geert Uytterhoeven wrote:
> Hi Richard,
> 
> On Mon, Aug 19, 2013 at 11:18 AM, Richard W.M. Jones <rjones@redhat.com> wrote:
> > On Sun, Aug 18, 2013 at 12:09:34AM +0200, Richard Weinberger wrote:
> >> UML's block device driver does not support write barriers,
> >> to support this this patch adds REQ_FLUSH suppport.
> >> Every time the block layer sends a REQ_FLUSH we fsync() now
> >> our backing file to guarantee data consistency.
> >
> > This fixes the sync problem I saw before.  So:
> 
> What's the impact on your performance figures?

It just moves the sync into the main process, thus making the
"write-no-upload" test time *increase* to what we expected (the same
as KVM).

This doesn't address the main performance issue, which appears to lie
in the serial port emulation.

Rich.

-- 
Richard Jones, Virtualization Group, Red Hat http://people.redhat.com/~rjones
virt-df lists disk usage of guests without needing to install any
software inside the virtual machine.  Supports Linux and Windows.
http://people.redhat.com/~rjones/virt-df/