[Qemu-devel] Re: KVM call agenda for Apr 27

[Gleb Natapov <gleb@redhat.com>]

On Tue, Apr 27, 2010 at 08:19:06AM -0500, Anthony Liguori wrote:
> On 04/27/2010 08:05 AM, Gleb Natapov wrote:
> >On Tue, Apr 27, 2010 at 08:00:02AM -0500, Anthony Liguori wrote:
> >>On 04/27/2010 06:11 AM, Gleb Natapov wrote:
> >>>Network cards have low number of rx/tx buffers interrupt. This is also
> >>>heuristic. Do you think driver should poll for this event instead and
> >>>NIC designers just wasted their time designing the feature?
> >>I don't see how the two cases are at all similar.
> >>
> >They are the same. They send notification when resource is low.
> >
> >>More importantly, I don't see what the burden is of polling when
> >>you're talking about a very unusual statistic that has a very
> >>limited use case.
> >>
> >Poll is the wrong answer. Always. The statistic is very common and has
> >wide use case unless you have unlimited storage.
> 
> Every management tool does polling in some form.  They'll poll CPU
> stats, I/O stats, etc.
> 
When there is no other way to get statistic polling is unavoidable, so
management tools do that. But here you propose to force management to do
polling for no good reason.

> The typical use-case for overcommitting storage is using file backed
> images.  Using a dynamically growing LVM volume is almost certainly
> unique to RHEV-M.
> 

What's the difference? If storage is overcommitted management wants to
know ahead of time that it needs to extend storage space. It may do
that by polling storage/qemu or by getting notifications asynchronously.

--
			Gleb.