[libvirt] [PATCH resend V10 03/12] Resctrl: Add new xml element to support cache tune

[Daniel P. Berrange]

On Wed, Mar 15, 2017 at 03:11:26PM +0100, Martin Kletzander wrote:
> On Mon, Mar 06, 2017 at 06:06:32PM +0800, Eli Qiao wrote:
> > This patch adds new xml element to support cache tune as:
> > 
> > <cputune>
> >  ...
> >  <cachetune id='1' host_id='0' type='l3' size='2816' unit='KiB'
> 
> Again, this was already discussed, probably, I just can't find the
> source of it.  But host_id actually already selects what cache is
> supposed to be used, so instead of type='l3' we only need scope='both'
> (or data/instruction) there.  Or am I missing something?  What I'm
> concerned about is that the host_id is mostly stable on one host (when
> the previously mentioned problems are fixed), but it will make no sense
> when the VM is migrated to another one.  Unfortunately, the only
> solution I can think of is using multiple keys to precisely describe the
> bank we want (e.g. host's cpu id, cache level and scope), but that seems
> very unclean.

I tend to view use of this cachetune setting as being similar to
using host CPU passthrough - you're intentionally trading off
migratability of your  guest to get a perf boost.

Even without the host_id bit, this is still non-portable, as you
might be requesting separate regions for code + data, but the
target host of migration may only support shared regions.

Regards,
Daniel
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