Re: frequent lockups in 3.18rc4

From: Andy Lutomirski
Date: Fri Nov 21 2014 - 15:17:03 EST

On Fri, Nov 21, 2014 at 12:14 PM, Josh Boyer <jwboyer@xxxxxxxxxxxxxxxxx> wrote:
> On Fri, Nov 21, 2014 at 2:52 PM, Andy Lutomirski <luto@xxxxxxxxxxxxxx> wrote:
>> On Fri, Nov 21, 2014 at 11:46 AM, Linus Torvalds
>> <torvalds@xxxxxxxxxxxxxxxxxxxx> wrote:
>>> On Fri, Nov 21, 2014 at 11:34 AM, Linus Torvalds
>>> <torvalds@xxxxxxxxxxxxxxxxxxxx> wrote:
>>>> So I kind of agree, but it wouldn't be my primary worry. My primary
>>>> worry is actually paravirt doing something insane.
>>> Btw, on that tangent, does anybody actually care about paravirt any more?
>> Amazon, for better or for worse.
>>> I'd love to start moving away from it. It makes a lot of the low-level
>>> code completely impossible to follow due to the random indirection
>>> through "native" vs "paravirt op table". Not just the page table
>>> handling, it's all over.
>>> Anybody who seriously does virtualization uses hw virtualization that
>>> is much better than it used to be. And the non-serious users aren't
>>> that performance-sensitive by definition.
>>> I note that the Fedora kernel config seems to include paravirt by
>>> default, so you get a lot of the crazy overheads..
>> I think that there is a move toward deprecating Xen PV in favor of
>> PVH, but we're not there yet.
> A move where? The Xen stuff in Fedora is ... not paid attention to
> very much. If there's something we should be looking at turning off
> (or on), we're happy to take suggestions.

A move in the Xen project. As I understand it, Xen wants to deprecate
PV in favor of PVH, but PVH is still experimental.

I think that dropping PARAVIRT in Fedora might be a bad idea for
several more releases, since that's likely to break the EC2 images.


> josh

Andy Lutomirski
AMA Capital Management, LLC
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