Re: Slow down with: 'Make "info qom-tree" show children sorted'

[David Gibson]

On Thu, 16 Jul 2020 07:37:17 +0200
Markus Armbruster <armbru@redhat.com> wrote:

> David Gibson <dgibson@redhat.com> writes:
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> > ... as you say, 256 shouldn't really be a problem.  I was concerned
> > about LMB DRCs rather than PCI DRCs.  To have that show up, you might
> > need to create a machine with a large difference between initial memory
> > and maxmem - I think you'll get a DRC object for every 256MiB in there,
> > which can easily get into the thousands for large (potential) memory
> > VMs.  
> 
> Okay, I can reproduce: with -m 256,128G, /machine has 549 children, of
> which 511 are spapr-drc-lmb.

Ok.

> > I don't know what the config was that showed up this problem in the
> > first place, and whether that could be the case there.  
> 
> Thomas reported device-introspect-test -m slow has become much slower
> for ppc64.  Bisection traced it to my commit e8c9e65816 "qom: Make "info
> qom-tree" show children sorted".  Uses default memory size, no
> spapr-drc-lmb as far as I remember.

Ok, I think that nixes my theory.

> >> >                 Though avoiding a n^2 behaviour here is probably a good
> >> > idea anyway.    
> >> 
> >> Agreed.  
> 
> Patch posted:
> 
>     Subject: [PATCH for-5.1 5/5] qom: Make info qom-tree sort children more 
> efficiently
>     Message-Id: <20200714160202.3121879-6-armbru@redhat.com>
> 


-- 
David Gibson <dgibson@redhat.com>
Principal Software Engineer, Virtualization, Red Hat

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