[lkml]   [2009]   [Nov]   [10]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
Messages in this thread
SubjectRe: virtio: Add memory statistics reporting to the balloon driver
Rusty Russell wrote:
> On Wed, 11 Nov 2009 08:22:42 am Anthony Liguori wrote:
>> Rusty Russell wrote:
>>> On Tue, 10 Nov 2009 03:02:06 am Adam Litke wrote:
>>>> A simpler approach is to collect memory statistics in the virtio
>>>> balloon driver and communicate them to the host via the device config space.
>>> There are two issues I see with this. First, there's an atomicity problem
>>> since you can't tell when the stats are consistent. Second, polling is
>>> ugly.
>>> A stats vq might solve this more cleanly?
>> This turns out to not work so nicely. You really need bidirectional
>> communication. You need to request that stats be collected and then you
>> need to tell the hypervisor about the stats that were collected. You
>> don't need any real correlation between requests and stat reports either.
> You register an outbuf at initialization time. The host hands it back when
> it wants you to refill it with stats.

That's strangely backwards. Guest send a stat buffer that's filled out,
host acks it when it wants another. That doesn't seem bizarre to you?

>> This really models how target/actual work and I think it suggests that
>> we want to reuse that mechanism for the stats too.
> Sure, I want to. You want to. It's simple.
> But the universe is remarkably indifferent to what we want. Is it actually
> sufficient or are we going to regret our laziness?

It's not laziness, it's consistency. How is actual different than free
memory or any other stat?

> Cheers,
> Rusty.


Anthony Liguori

 \ /
  Last update: 2009-11-11 01:11    [W:0.244 / U:4.292 seconds]
©2003-2018 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site