Re: [PATCH] kernel/resource: optimize find_next_iomem_res

[Andy Shevchenko]

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).

P.S> I'm not so sure about this change. It needs a thoroughly testing, esp.
in PCI case. Cc'ing to Ilpo.

-- 
With Best Regards,
Andy Shevchenko