Clarification regarding xen toolstack for booting a pv guest

Clarification regarding xen toolstack for booting a pv guest

[sainath grandhi]

Hello all,



I was measuring amount of time taken on host by the Xen toolstack
while launching a PV guest.

I notice that there is around 2-3 seconds of time spent on dom0 by
toolstack before guest starts executing. Significant amount of time is
taken in the function xc_dom_boot_mem_init, around 2 seconds for a
guest memory of 2 GB

This code does allocate guest memory and mappings and amount of time
this function takes increases proportionally with increasing requested
guest memory in the guest config file.

Has anyone noticed similar thing? Is ~2 seconds of wall clock time
reasonable for guest memory mapping?

Thanks

Re: Clarification regarding xen toolstack for booting a pv guest

[Wei Liu]

On Mon, Aug 10, 2015 at 05:00:51PM -0700, sainath grandhi wrote:
> Hello all,
> 
> 
> 
> I was measuring amount of time taken on host by the Xen toolstack
> while launching a PV guest.
> 
> I notice that there is around 2-3 seconds of time spent on dom0 by
> toolstack before guest starts executing. Significant amount of time is
> taken in the function xc_dom_boot_mem_init, around 2 seconds for a
> guest memory of 2 GB
> 
> This code does allocate guest memory and mappings and amount of time
> this function takes increases proportionally with increasing requested
> guest memory in the guest config file.
> 
> Has anyone noticed similar thing? Is ~2 seconds of wall clock time
> reasonable for guest memory mapping?

I guess it is because Dom0 has to balloon down to free up memory for
guest.

What is your Xen command line? Have you tried putting
dom0_mem=512M,max:512M there?

Wei.

> 
> Thanks
> 
> _______________________________________________
> Xen-devel mailing list
> Xen-devel@lists.xen.org
> http://lists.xen.org/xen-devel

Re: Clarification regarding xen toolstack for booting a pv guest

[Wei Liu]

On Tue, Aug 11, 2015 at 01:51:10AM +0100, Wei Liu wrote:
> On Mon, Aug 10, 2015 at 05:00:51PM -0700, sainath grandhi wrote:
> > Hello all,
> > 
> > 
> > 
> > I was measuring amount of time taken on host by the Xen toolstack
> > while launching a PV guest.
> > 
> > I notice that there is around 2-3 seconds of time spent on dom0 by
> > toolstack before guest starts executing. Significant amount of time is
> > taken in the function xc_dom_boot_mem_init, around 2 seconds for a
> > guest memory of 2 GB
> > 
> > This code does allocate guest memory and mappings and amount of time
> > this function takes increases proportionally with increasing requested
> > guest memory in the guest config file.
> > 
> > Has anyone noticed similar thing? Is ~2 seconds of wall clock time
> > reasonable for guest memory mapping?
> 
> I guess it is because Dom0 has to balloon down to free up memory for
> guest.
> 
> What is your Xen command line? Have you tried putting
> dom0_mem=512M,max:512M there?
> 

And I forgot to mention there is a patch to make PV guest creation
faster by using superpage and batching.

See 415b58c1 and 826ca36fa3 in xen-unstable tree.

Wei.

> Wei.
> 
> > 
> > Thanks
> > 
> > _______________________________________________
> > Xen-devel mailing list
> > Xen-devel@lists.xen.org
> > http://lists.xen.org/xen-devel