Re: [PATCH 11/12] drm/i915: Extend GET_APERTURE ioctl to report available map space

[Tvrtko Ursulin <tvrtko.ursulin@linux.intel.com>]

On 21/04/16 15:46, Chris Wilson wrote:
> On Thu, Apr 21, 2016 at 03:04:52PM +0100, Tvrtko Ursulin wrote:
>>
>> Hi,
>>
>> On 20/04/16 12:17, ankitprasad.r.sharma@intel.com wrote:
>>> +	mutex_unlock(&dev->struct_mutex);
>>> +
>>> +	seq_printf(m, "Total size of the GTT: %llu bytes\n",
>>> +		   arg.aper_size);
>>> +	seq_printf(m, "Available space in the GTT: %llu bytes\n",
>>> +		   arg.aper_available_size);
>>> +	seq_printf(m, "Total space in the mappable aperture: %llu bytes\n",
>>> +		   arg.map_total_size);
>>> +	seq_printf(m, "Available space in the mappable aperture: %llu bytes\n",
>>> +		   map_space);
>>> +	seq_printf(m, "Single largest space in the mappable aperture: %llu bytes\n",
>>> +		   map_largest);
>>> +	seq_printf(m, "Available space for fences: %llu bytes\n",
>>> +		   fence_space);
>>> +	seq_printf(m, "Single largest fence available: %llu bytes\n",
>>> +		   fence_largest);
>>> +
>>> +	return 0;
>>> +}
>>> +
>>
>> In general I find this a lot of code for a feature of questionable
>> utility. As such I would prefer someone really stated the need for
>> this and explained how it really is useful - even though whetever
>> number they get from this may be completely irrelevant by the time
>> it is acted upon.
>
> Yes, with the exception of the size of the mappable aperture, this is
> really is debug info. It will get automatically dumped by userspace
> when it sees an ENOSPC, and that may prove enough to solve the riddle of
> why it failed. However, this information is terrible outdated and now
> longer of such relevance.
>
> As for the mappable aperture size, there has been a request many years
> ago! could we provide it without resorting to a privilege operation. I
> guess by know that request has died out - but there is still the issue
> with libpciassess that make it unsuitable for use inside a library where
> one may want to avoid it and use a simple ioctl on the device you
> already have open.
>
> Yes, it is meh.

Aperture size in the ioctl is fine I think, just that detection caveat 
what I asked in the other reply.

Here I wanted to suggest dropping all the non-trivial debugfs stuff and 
just leave the info queried via i915_gem_get_aperture ioctl. So 
effectively dropping the list traversal and vma sorting bits.

Regards,

Tvrtko
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