Re: [Intel-gfx] [PATCH 0/7] Per client engine busyness

["Christian König" <christian.koenig@amd.com>]

Am 20.05.21 um 16:11 schrieb Daniel Vetter:
> On Wed, May 19, 2021 at 11:17:24PM +0000, Nieto, David M wrote:
>> [AMD Official Use Only]
>>
>> Parsing over 550 processes for fdinfo is taking between 40-100ms single
>> threaded in a 2GHz skylake IBRS within a VM using simple string
>> comparisons and DIRent parsing. And that is pretty much the worst case
>> scenario with some more optimized implementations.
> I think this is plenty ok, and if it's not you could probably make this
> massively faster with io_uring for all the fs operations and whack a
> parser-generator on top for real parsing speed.

Well if it becomes a problem fixing the debugfs "clients" file and 
making it sysfs shouldn't be much of a problem later on.

Christian.

>
> So imo we shouldn't worry about algorithmic inefficiency of the fdinfo
> approach at all, and focuse more on trying to reasonably (but not too
> much, this is still drm render stuff after all) standardize how it works
> and how we'll extend it all. I think there's tons of good suggestions in
> this thread on this topic already.
>
> /me out
> -Daniel
>
>> David
>> ________________________________
>> From: Daniel Vetter <daniel@ffwll.ch>
>> Sent: Wednesday, May 19, 2021 11:23 AM
>> To: Tvrtko Ursulin <tvrtko.ursulin@linux.intel.com>
>> Cc: Daniel Stone <daniel@fooishbar.org>; jhubbard@nvidia.com <jhubbard@nvidia.com>; nouveau@lists.freedesktop.org <nouveau@lists.freedesktop.org>; Intel Graphics Development <Intel-gfx@lists.freedesktop.org>; Maling list - DRI developers <dri-devel@lists.freedesktop.org>; Simon Ser <contact@emersion.fr>; Koenig, Christian <Christian.Koenig@amd.com>; aritger@nvidia.com <aritger@nvidia.com>; Nieto, David M <David.Nieto@amd.com>
>> Subject: Re: [Intel-gfx] [PATCH 0/7] Per client engine busyness
>>
>> On Wed, May 19, 2021 at 6:16 PM Tvrtko Ursulin
>> <tvrtko.ursulin@linux.intel.com> wrote:
>>>
>>> On 18/05/2021 10:40, Tvrtko Ursulin wrote:
>>>> On 18/05/2021 10:16, Daniel Stone wrote:
>>>>> Hi,
>>>>>
>>>>> On Tue, 18 May 2021 at 10:09, Tvrtko Ursulin
>>>>> <tvrtko.ursulin@linux.intel.com> wrote:
>>>>>> I was just wondering if stat(2) and a chrdev major check would be a
>>>>>> solid criteria to more efficiently (compared to parsing the text
>>>>>> content) detect drm files while walking procfs.
>>>>> Maybe I'm missing something, but is the per-PID walk actually a
>>>>> measurable performance issue rather than just a bit unpleasant?
>>>> Per pid and per each open fd.
>>>>
>>>> As said in the other thread what bothers me a bit in this scheme is that
>>>> the cost of obtaining GPU usage scales based on non-GPU criteria.
>>>>
>>>> For use case of a top-like tool which shows all processes this is a
>>>> smaller additional cost, but then for a gpu-top like tool it is somewhat
>>>> higher.
>>> To further expand, not only cost would scale per pid multiplies per open
>>> fd, but to detect which of the fds are DRM I see these three options:
>>>
>>> 1) Open and parse fdinfo.
>>> 2) Name based matching ie /dev/dri/.. something.
>>> 3) Stat the symlink target and check for DRM major.
>> stat with symlink following should be plenty fast.
>>
>>> All sound quite sub-optimal to me.
>>>
>>> Name based matching is probably the least evil on system resource usage
>>> (Keeping the dentry cache too hot? Too many syscalls?), even though
>>> fundamentally I don't it is the right approach.
>>>
>>> What happens with dup(2) is another question.
>> We need benchmark numbers showing that on anything remotely realistic
>> it's an actual problem. Until we've demonstrated it's a real problem
>> we don't need to solve it.
>>
>> E.g. top with any sorting enabled also parses way more than it
>> displays on every update. It seems to be doing Just Fine (tm).
>>
>>> Does anyone have any feedback on the /proc/<pid>/gpu idea at all?
>> When we know we have a problem to solve we can take a look at solutions.
>> -Daniel
>> --
>> Daniel Vetter
>> Software Engineer, Intel Corporation
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