Re: [Qemu-devel] [RFC 1/2] spapr: Reverse order of hotpluggable cpus list

[Igor Mammedov]

On Thu, 21 Jul 2016 23:07:06 +1000
David Gibson <address@hidden> wrote:

> On Wed, Jul 20, 2016 at 09:01:11AM +0200, Peter Krempa wrote:
> > On Wed, Jul 20, 2016 at 11:00:05 +1000, David Gibson wrote:  
> > > On Tue, Jul 19, 2016 at 01:52:40PM +0200, Peter Krempa wrote:  
> > > > On Mon, Jul 18, 2016 at 19:19:19 +1000, David Gibson wrote:  
> > > > > The spapr implementation of query-hotpluggable-cpus builds the list of
> > > > > hotpluggable cores from the end (most removed from the list head)
> > > > > because that's the easiest way with a singly linked list.  Because it
> > > > > also traverses the possible CPU cores starting from low indexes the
> > > > > resulting list has the cpu cores listed in reverse order by core-id.
> > > > > 
> > > > > That's not generally harmful, but it means the output from "info
> > > > > hotpluggable-cpus" is a little harder to read than it could be.
> > > > > 
> > > > > Therefore, traverse the cpus in reverse order so that the final list
> > > > > ends up in increasing-core-id order.  
> > > > 
> > > > To make this interface usable with in-order hotplug the ordering of the
> > > > entries should be codified in the schema documentation. (see my response
> > > > on the cover letter for justification).  
> > > 
> > > I'm not really sure what you mean by this.  
> > 
> > Currently the order of entries in reply of query-hotpluggable-cpus is
> > arbitrary as this patch hints.
> > 
> > If qemu won't support arbitrary order hotplug but libvirt should be able
> > to use the new interface, then the order of replies of
> > query-hotpluggable-cpus need to corelate (in a documented fashion) with
> > the order we need to plug the cpus in. By not documenting any order
> > libvirt can just guess it (by reimplementing the algorithm in qemu).  
> 
> > I've pointed this out in a sub-thread of the cover-letter.  
> 
> Right, that's kind of the point of this patch - it makes the order
> returned by query-hotpluggable-cpus match the required order for "in
> order" hotplug.  That may not be necessary so - it looks like between
> Igor and myself we might have an eleventh hour way of enabling
> any-order hotplug.
> 
> That said, I'm still inclined to push this patch at some point for the
> sake of easier to read debugging output.
it's qmp command output intended for machine parsing, so don't really need it