[RFC PATCH v2 17/17] WIP: drm/tegra: Implement new UAPI

[Dmitry Osipenko]

09.09.2020 11:19, Mikko Perttunen пишет:
...
>>> +    if (!job_data->used_mappings)
>>> +        return -ENOMEM;
>>> +
>>> +    for (i = 0; i < args->num_bufs; i++) {
>>> +        copy_err = copy_from_user(&buf, user_bufs_ptr+i, sizeof(buf));
>>
>> Whole array always should be copied at once. Please keep in mind that
>> each copy_from_user() has a cpu-time cost, there should maximum up to 2
>> copyings per job.
>>
> 
> OK. BTW, do you have some reference/numbers for this or is it based on
> grate-driver experience?

I had numbers about 2 years ago while was profiling job submission
latency using host1x-tests and for a simple jobs there was a visible
difference caused by each copy_from_user(), kmalloc() and having
firewall functions uninlined.

Of course it wasn't critical, but it's also not difficult to optimize
such things.