Re: [PATCH] kernel/resource: optimize find_next_iomem_res

Ilpo Järvinen
2024-06-03T07:24:47Z

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On Sun, 2 Jun 2024, Andy Shevchenko wrote:

> On Fri, May 31, 2024 at 02:31:45PM -0700, Chia-I Wu wrote:
> > On Fri, May 31, 2024 at 1:57 AM Andy Shevchenko <
> > andriy.shevchenko@linux.intel.com> wrote:
> > > On Thu, May 30, 2024 at 10:36:57PM -0700, Chia-I Wu wrote:
>
> ...
>
> > > P.S> I'm not so sure about this change. It needs a thoroughly testing, esp.
> > > in PCI case. Cc'ing to Ilpo.
>
> > What's special about PCI?
>
> PCI, due to its nature, may rebuild resources either by shrinking or expanding
> of the entire subtree after the PCI bridge in question. And this may happen at
> run-time due to hotplug support. But I'm not a deep expert in this area, Ilpo
> knows much more than me.

There is code which clearly tries to do expanding resource but that
usually fails to work as intended because of a parent resource whose size
is fixed because it's already assigned.

Some other code might block shrinking too under certain conditions.

This area would need to be reworked in PCI core but it's massive and
scary looking change.

--
i.