Re: [Xen-devel] NUMA TODO-list for xen-devel

[Dan Magenheimer <dan.magenheimer@xxxxxxxxxx>]

> From: Jan Beulich [mailto:JBeulich@xxxxxxxx]
> Subject: RE: [Xen-devel] NUMA TODO-list for xen-devel
> 
> >>> On 04.08.12 at 00:34, Dan Magenheimer <dan.magenheimer@xxxxxxxxxx> wrote:
> >>  From: Jan Beulich [mailto:JBeulich@xxxxxxxx]
> >> The question is whether trading functionality for performance
> >> is an acceptable choice.
> >
> > If there were a lwn.net equivalent for Xen, I'd be pushing to get
> > quoted on the following:
> >
> > "Virtualization: You can have flexibility or you can have performance.
> > Pick one."
> >
> > A couple of years ago when NUMA was first being extensively discussed
> > for Xen, I suggested that this should really be a "top level" flag
> > that a sysadmin should be able to select: Either optimize for
> > performance or optimize for flexibility.  Then Xen and the Xen tools
> > should "do the right thing" depending on the selection.
> >
> > I still think this is a good way to surface the tradeoffs for
> > a very complex problem to the vast majority of users/admins.
> > Clearly they will want "both" but forcing the choice will
> > provoke more thought about their use model, as well as provide
> > important guidance to the underlying implementations.
> 
> I would expect a good part to pick performance, and then
> go whine about something not working in an emergency. On
> xen-devel one could respond with this-is-what-you-get, but
> you can't necessarily do so to paying customers...

Well, you can, but you have to first convince marketing that
virtualization doesn't solve all problems for all users all the
time. :-)

The two options would have to be clearly documented as:

"flexibility-is-my-highest-priority-and-performance-is-second-priority"

and

"performance-is-my-highest-priority-and-flexibility-is-second-priority"

and when a user selects the latter, they should be prompted with

"Are you really sure you want to use virtualization instead of bare metal?"

Sigh. We can only wish.
Dan

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