[Intel-gfx] [PATCH 4/4] drm/i915/perf: Map OA buffer to user space for gen12 performance query

[Umesh Nerlige Ramappa]

On Fri, Jul 24, 2020 at 08:46:16PM +0100, Chris Wilson wrote:
>Quoting Umesh Nerlige Ramappa (2020-07-24 20:35:11)
>> I agree, but strangely, with mmap sequence below, I don't see
>> i915_perf_release() called at all.  So destroy() is not called.
>>
>> perf_fd = i915_perf_open_ioctl()
>> mmap(..., perf_fd...)
>> close(perf_fd)
>> delay for a few seconds.
>>
>> If I call munmap() after the close(), I see i915_perf_release() ->
>> destroy() -> unmap_mapping_range()
>
>Hmm, vma->vm_file is pointing to the perf-fd. Ah, that's a big
>difference to what I'm used to. So all the references are handled for
>you by the correct vma->vm_file, and you don't need the
>vm_open/vm_close, the kref or the closed. Sorry.

no worries at all. This is all new for me, so I appreciate all your 
prompt guidance that helped me look into this implementation in detail.

Thanks,
Umesh

>-Chris