Re: [Xen-devel] [PATCH] xen: Implement domain runstates

[Bruce Edge <bruce.edge@xxxxxxxxx>]

On Tue, Nov 23, 2010 at 7:48 AM, George Dunlap <George.Dunlap@xxxxxxxxxxxxx> wrote:

On 23/11/10 15:00, Keir Fraser wrote:

Well, actually what we care about is #users-who-care. Plumbing into xentop
to satisfy an acceptance criteria is probably misguided. Reducing
patch-queue length just to make a patch-queue short is also probably
misguided.

I wouldn't offer to put it in xentop just because I wanted to get the patch out of the patchqueue.  I think it's a useful feature, that many people would use if they knew about it.  If I didn't think it was useful, by far the simplest way to get it out of the patchqueue would be to simply remove the functionality from the next release of XenServer.

I think the "wait for people to ask for it" won't work very well for this particular feature, because it's not the kind of thing I think most people would think to ask for.  A bit like tmem -- I think it's a solution to a problem that people have that's very non-obvious, and must therefore be suggested to people rather than waiting for them to ask for it.  I could write a blog post about it or otherwise try to promote the idea, but how many people are going to download a patch in order to try it out?

Irrespective of the nature of the suggested functionality, I do agree that xen users will be more likely to try something if it's part of the default build, especially if the benefit is not immediately obvious. With all the complexity associated with any virtualization project, I think that many integrators don't have the time to experiment with every possible option included in the "off the shelf" Xen, not to mention those that require explicit patching and manual inclusion.
That said I would try this as a "VCPU allocation suitability" metric for any xen system. The ability to see this data 'at a glance' would be beneficial to admins and system architects.
A lot of data is available if you know how to get it. That is very different from presenting that data in an easily digestible format requiring no work to use.

-Bruce

 

(I'm aware the difference is that tmem's effectiveness can be measured with benchmarks while this feature cannot; I'm just saying that in both cases, you'd be waiting for a long time for people to demand it.)

xenalyze will calculate and report domain runstate numbers based on vcpu runstate_change records, and I've found it useful to get a rough idea what's going on when I get traces in from the field.

Of course there's no rush, but it's likely to be forgotten about for another two years. :-)  (It's already been in the XS patchqueue since September 2008.)

 -George

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