[igt-dev] [PATCH 4/5] tools/i915-perf: Add mmapped OA buffer support to i915-perf-recorder

[Dixit, Ashutosh]

On Tue, 03 Aug 2021 13:07:36 -0700, Umesh Nerlige Ramappa wrote:
>
> Currently report from OA buffer are read from the perf_fd. The kernel
> patches enable mmaping the OA buffer into user space to allow for faster
> report queries across different platforms and engines.
>
> Enable OA buffer to be mmaped by the recorder tool based on command line
> option -M.
>
> Example:
> i915-perf-recorder -m RenderBasic -s 8000 -k "mono" -M
>
> The recorder processes the mmaped OA buffer by periodically reading the
> OA TAIL PTR register from a batch and determining the number of reports
> available. These reports are then logged in the circular-buffer as
> INTEL_PERF_RECORD_TYPE_MULTIPLE_SAMPLE records. In this implementation
> the periodicity of checking the TAIL is the same as writing correlation
> timestamps (1 sec).

I haven't looked at everything so correct me if I am wrong but I have this
other concern about INTEL_PERF_RECORD_TYPE_MULTIPLE_SAMPLE. What is the
reason for introducing this? I would have thought that whether OA data has
been collected using read's or mmap is a property only of the recorder and
should not be exposed to the reader or gpuvis. So in the mmap case the
recorder should basically do what the kernel does but not introduce a new
perf record type. But now we are seeing changes both in the reader and
gpuvis because we have introduced INTEL_PERF_RECORD_TYPE_MULTIPLE_SAMPLE?
Thanks.