On Fri, May 31, 2024 at 1:57 AM Andy Shevchenko <andriy.shevchenko@xxxxxxxxxxxxxxx> wrote:
On Thu, May 30, 2024 at 10:36:57PM -0700, Chia-I Wu wrote:
> We can skip children resources when the parent resource does not cover
> the range.
>
> This should help vmf_insert_* users on x86, such as several DRM drivers.
> On my AMD Ryzen 5 7520C, when streaming data from cpu memory into amdgpu
> bo, the throughput goes from 5.1GB/s to 6.6GB/s. perf report says
>
> 34.69%--__do_fault
> 34.60%--amdgpu_gem_fault
> 34.00%--ttm_bo_vm_fault_reserved
> 32.95%--vmf_insert_pfn_prot
> 25.89%--track_pfn_insert
> 24.35%--lookup_memtype
> 21.77%--pat_pagerange_is_ram
> 20.80%--walk_system_ram_range
> 17.42%--find_next_iomem_res
>
> before this change, and
>
> 26.67%--__do_fault
> 26.57%--amdgpu_gem_fault
> 25.83%--ttm_bo_vm_fault_reserved
> 24.40%--vmf_insert_pfn_prot
> 14.30%--track_pfn_insert
> 12.20%--lookup_memtype
> 9.34%--pat_pagerange_is_ram
> 8.22%--walk_system_ram_range
> 5.09%--find_next_iomem_res
>
> after.
Is there any documentation that explicitly says that the children resources
must not overlap parent's one? Do we have some test cases? (Either way they
needs to be added / expanded).
I think it's the opposite. The assumption here is that a child is always a subset of its parent. Thus, if the range to be checked is not covered by a parent, we can skip the children.
That's guaranteed by __request_resource. I am less sure about __insert_resource but it appears to be the case too. FWIW, resource_is_exclusive has the same assumption already.
It looks like I need to do some refactoring to add tests.
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?
--
With Best Regards,
Andy Shevchenko
