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@xxxxxxxx>
Sent: Wednesday, May 19, 2021 11:23 AM
To: Tvrtko Ursulin <tvrtko.ursulin@xxxxxxxxxxxxxxx>
Cc: Daniel Stone <daniel@xxxxxxxxxxxxx>; jhubbard@xxxxxxxxxx <jhubbard@xxxxxxxxxx>; nouveau@xxxxxxxxxxxxxxxxxxxxx <nouveau@xxxxxxxxxxxxxxxxxxxxx>; Intel Graphics Development <Intel-gfx@xxxxxxxxxxxxxxxxxxxxx>; Maling list - DRI developers <dri-devel@xxxxxxxxxxxxxxxxxxxxx>; Simon Ser <contact@xxxxxxxxxxx>; Koenig, Christian <Christian.Koenig@xxxxxxx>; aritger@xxxxxxxxxx <aritger@xxxxxxxxxx>; Nieto, David M <David.Nieto@xxxxxxx>
Subject: Re: [Intel-gfx] [PATCH 0/7] Per client engine busyness
On Wed, May 19, 2021 at 6:16 PM Tvrtko Ursulin
<tvrtko.ursulin@xxxxxxxxxxxxxxx> 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@xxxxxxxxxxxxxxx> 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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