Messages in this thread | | | From | Dan Williams <> | Date | Thu, 2 Sep 2021 08:54:47 -0700 | Subject | Re: [PATCH v3 1/3] kernel/resource: clean up and optimize iomem_is_exclusive() |
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On Thu, Sep 2, 2021 at 12:52 AM David Hildenbrand <david@redhat.com> wrote: > > On 01.09.21 21:43, Williams, Dan J wrote: > > On Tue, 2021-08-31 at 22:21 +0200, David Hildenbrand wrote: > >> We end up traversing subtrees of ranges we are not interested in; let's > >> optimize this case, skipping such subtrees, cleaning up the function a bit. > >> > >> Signed-off-by: David Hildenbrand <david@redhat.com> > >> --- > >> kernel/resource.c | 25 ++++++++++++++++++++----- > >> 1 file changed, 20 insertions(+), 5 deletions(-) > > > > That diffstat does not come across as "cleanup", and the skip_children > > flag changing values mid-iteration feels tricky. Is there a win here, > > the same number of entries still need to be accessed, right? > > Right, most of the patch changes falls under "optimize". The cleanup is > using for_each_resource() and not using r_next(NULL, p, &l). Sure, I > could have split this up but then I'd just introduce for_each_resource() > to modify it immediately again. > > > Let's take a look at /proc/iomem on my notebook: > > 00000000-00000fff : Reserved > 00001000-00057fff : System RAM > 00058000-00058fff : Reserved > 00059000-0009cfff : System RAM > 0009d000-000fffff : Reserved > 000a0000-000bffff : PCI Bus 0000:00 > 000c0000-000c3fff : PCI Bus 0000:00 > 000c4000-000c7fff : PCI Bus 0000:00 > 000c8000-000cbfff : PCI Bus 0000:00 > 000cc000-000cffff : PCI Bus 0000:00 > 000d0000-000d3fff : PCI Bus 0000:00 > 000d4000-000d7fff : PCI Bus 0000:00 > 000d8000-000dbfff : PCI Bus 0000:00 > 000dc000-000dffff : PCI Bus 0000:00 > 000e0000-000e3fff : PCI Bus 0000:00 > 000e4000-000e7fff : PCI Bus 0000:00 > 000e8000-000ebfff : PCI Bus 0000:00 > 000ec000-000effff : PCI Bus 0000:00 > 000f0000-000fffff : PCI Bus 0000:00 > 000f0000-000fffff : System ROM > 00100000-3fffffff : System RAM > 40000000-403fffff : Reserved > 40000000-403fffff : pnp 00:00 > 40400000-80a79fff : System RAM > ... > > Why should we take a look at any children of "0009d000-000fffff : > Reserved" if we can just skip these 15 items directly because the parent > range is not of interest?
Oh I misread, it never loads the child entries into cache, so it's a true skip and not a continue.
You can add:
Reviewed-by: Dan Williams <dan.j.williams@intel.com>
...I was going to say it should be named for_each_top_resource(), but we can cross that bridge when / if something needs an iterator that includes children.
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