Re: [PATCH v3 6/7] drm: Add fdinfo memory stats

[Rob Clark]

On Mon, Apr 17, 2023 at 7:20 AM Tvrtko Ursulin
<tvrtko.ursulin@xxxxxxxxxxxxxxx> wrote:
>
>
> On 17/04/2023 14:42, Rob Clark wrote:
> > On Mon, Apr 17, 2023 at 4:10 AM Tvrtko Ursulin
> > <tvrtko.ursulin@xxxxxxxxxxxxxxx> wrote:
> >>
> >>
> >> On 16/04/2023 08:48, Daniel Vetter wrote:
> >>> On Fri, Apr 14, 2023 at 06:40:27AM -0700, Rob Clark wrote:
> >>>> On Fri, Apr 14, 2023 at 1:57 AM Tvrtko Ursulin
> >>>> <tvrtko.ursulin@xxxxxxxxxxxxxxx> wrote:
> >>>>>
> >>>>>
> >>>>> On 13/04/2023 21:05, Daniel Vetter wrote:
> >>>>>> On Thu, Apr 13, 2023 at 05:40:21PM +0100, Tvrtko Ursulin wrote:
> >>>>>>>
> >>>>>>> On 13/04/2023 14:27, Daniel Vetter wrote:
> >>>>>>>> On Thu, Apr 13, 2023 at 01:58:34PM +0100, Tvrtko Ursulin wrote:
> >>>>>>>>>
> >>>>>>>>> On 12/04/2023 20:18, Daniel Vetter wrote:
> >>>>>>>>>> On Wed, Apr 12, 2023 at 11:42:07AM -0700, Rob Clark wrote:
> >>>>>>>>>>> On Wed, Apr 12, 2023 at 11:17 AM Daniel Vetter <daniel@xxxxxxxx> wrote:
> >>>>>>>>>>>>
> >>>>>>>>>>>> On Wed, Apr 12, 2023 at 10:59:54AM -0700, Rob Clark wrote:
> >>>>>>>>>>>>> On Wed, Apr 12, 2023 at 7:42 AM Tvrtko Ursulin
> >>>>>>>>>>>>> <tvrtko.ursulin@xxxxxxxxxxxxxxx> wrote:
> >>>>>>>>>>>>>>
> >>>>>>>>>>>>>>
> >>>>>>>>>>>>>> On 11/04/2023 23:56, Rob Clark wrote:
> >>>>>>>>>>>>>>> From: Rob Clark <robdclark@xxxxxxxxxxxx>
> >>>>>>>>>>>>>>>
> >>>>>>>>>>>>>>> Add support to dump GEM stats to fdinfo.
> >>>>>>>>>>>>>>>
> >>>>>>>>>>>>>>> v2: Fix typos, change size units to match docs, use div_u64
> >>>>>>>>>>>>>>> v3: Do it in core
> >>>>>>>>>>>>>>>
> >>>>>>>>>>>>>>> Signed-off-by: Rob Clark <robdclark@xxxxxxxxxxxx>
> >>>>>>>>>>>>>>> Reviewed-by: Emil Velikov <emil.l.velikov@xxxxxxxxx>
> >>>>>>>>>>>>>>> ---
> >>>>>>>>>>>>>>>        Documentation/gpu/drm-usage-stats.rst | 21 ++++++++
> >>>>>>>>>>>>>>>        drivers/gpu/drm/drm_file.c            | 76 +++++++++++++++++++++++++++
> >>>>>>>>>>>>>>>        include/drm/drm_file.h                |  1 +
> >>>>>>>>>>>>>>>        include/drm/drm_gem.h                 | 19 +++++++
> >>>>>>>>>>>>>>>        4 files changed, 117 insertions(+)
> >>>>>>>>>>>>>>>
> >>>>>>>>>>>>>>> diff --git a/Documentation/gpu/drm-usage-stats.rst b/Documentation/gpu/drm-usage-stats.rst
> >>>>>>>>>>>>>>> index b46327356e80..b5e7802532ed 100644
> >>>>>>>>>>>>>>> --- a/Documentation/gpu/drm-usage-stats.rst
> >>>>>>>>>>>>>>> +++ b/Documentation/gpu/drm-usage-stats.rst
> >>>>>>>>>>>>>>> @@ -105,6 +105,27 @@ object belong to this client, in the respective memory region.
> >>>>>>>>>>>>>>>        Default unit shall be bytes with optional unit specifiers of 'KiB' or 'MiB'
> >>>>>>>>>>>>>>>        indicating kibi- or mebi-bytes.
> >>>>>>>>>>>>>>>
> >>>>>>>>>>>>>>> +- drm-shared-memory: <uint> [KiB|MiB]
> >>>>>>>>>>>>>>> +
> >>>>>>>>>>>>>>> +The total size of buffers that are shared with another file (ie. have more
> >>>>>>>>>>>>>>> +than a single handle).
> >>>>>>>>>>>>>>> +
> >>>>>>>>>>>>>>> +- drm-private-memory: <uint> [KiB|MiB]
> >>>>>>>>>>>>>>> +
> >>>>>>>>>>>>>>> +The total size of buffers that are not shared with another file.
> >>>>>>>>>>>>>>> +
> >>>>>>>>>>>>>>> +- drm-resident-memory: <uint> [KiB|MiB]
> >>>>>>>>>>>>>>> +
> >>>>>>>>>>>>>>> +The total size of buffers that are resident in system memory.
> >>>>>>>>>>>>>>
> >>>>>>>>>>>>>> I think this naming maybe does not work best with the existing
> >>>>>>>>>>>>>> drm-memory-<region> keys.
> >>>>>>>>>>>>>
> >>>>>>>>>>>>> Actually, it was very deliberate not to conflict with the existing
> >>>>>>>>>>>>> drm-memory-<region> keys ;-)
> >>>>>>>>>>>>>
> >>>>>>>>>>>>> I wouldn't have preferred drm-memory-{active,resident,...} but it
> >>>>>>>>>>>>> could be mis-parsed by existing userspace so my hands were a bit tied.
> >>>>>>>>>>>>>
> >>>>>>>>>>>>>> How about introduce the concept of a memory region from the start and
> >>>>>>>>>>>>>> use naming similar like we do for engines?
> >>>>>>>>>>>>>>
> >>>>>>>>>>>>>> drm-memory-$CATEGORY-$REGION: ...
> >>>>>>>>>>>>>>
> >>>>>>>>>>>>>> Then we document a bunch of categories and their semantics, for instance:
> >>>>>>>>>>>>>>
> >>>>>>>>>>>>>> 'size' - All reachable objects
> >>>>>>>>>>>>>> 'shared' - Subset of 'size' with handle_count > 1
> >>>>>>>>>>>>>> 'resident' - Objects with backing store
> >>>>>>>>>>>>>> 'active' - Objects in use, subset of resident
> >>>>>>>>>>>>>> 'purgeable' - Or inactive? Subset of resident.
> >>>>>>>>>>>>>>
> >>>>>>>>>>>>>> We keep the same semantics as with process memory accounting (if I got
> >>>>>>>>>>>>>> it right) which could be desirable for a simplified mental model.
> >>>>>>>>>>>>>>
> >>>>>>>>>>>>>> (AMD needs to remind me of their 'drm-memory-...' keys semantics. If we
> >>>>>>>>>>>>>> correctly captured this in the first round it should be equivalent to
> >>>>>>>>>>>>>> 'resident' above. In any case we can document no category is equal to
> >>>>>>>>>>>>>> which category, and at most one of the two must be output.)
> >>>>>>>>>>>>>>
> >>>>>>>>>>>>>> Region names we at most partially standardize. Like we could say
> >>>>>>>>>>>>>> 'system' is to be used where backing store is system RAM and others are
> >>>>>>>>>>>>>> driver defined.
> >>>>>>>>>>>>>>
> >>>>>>>>>>>>>> Then discrete GPUs could emit N sets of key-values, one for each memory
> >>>>>>>>>>>>>> region they support.
> >>>>>>>>>>>>>>
> >>>>>>>>>>>>>> I think this all also works for objects which can be migrated between
> >>>>>>>>>>>>>> memory regions. 'Size' accounts them against all regions while for
> >>>>>>>>>>>>>> 'resident' they only appear in the region of their current placement, etc.
> >>>>>>>>>>>>>
> >>>>>>>>>>>>> I'm not too sure how to rectify different memory regions with this,
> >>>>>>>>>>>>> since drm core doesn't really know about the driver's memory regions.
> >>>>>>>>>>>>> Perhaps we can go back to this being a helper and drivers with vram
> >>>>>>>>>>>>> just don't use the helper?  Or??
> >>>>>>>>>>>>
> >>>>>>>>>>>> I think if you flip it around to drm-$CATEGORY-memory{-$REGION}: then it
> >>>>>>>>>>>> all works out reasonably consistently?
> >>>>>>>>>>>
> >>>>>>>>>>> That is basically what we have now.  I could append -system to each to
> >>>>>>>>>>> make things easier to add vram/etc (from a uabi standpoint)..
> >>>>>>>>>>
> >>>>>>>>>> What you have isn't really -system, but everything. So doesn't really make
> >>>>>>>>>> sense to me to mark this -system, it's only really true for integrated (if
> >>>>>>>>>> they don't have stolen or something like that).
> >>>>>>>>>>
> >>>>>>>>>> Also my comment was more in reply to Tvrtko's suggestion.
> >>>>>>>>>
> >>>>>>>>> Right so my proposal was drm-memory-$CATEGORY-$REGION which I think aligns
> >>>>>>>>> with the current drm-memory-$REGION by extending, rather than creating
> >>>>>>>>> confusion with different order of key name components.
> >>>>>>>>
> >>>>>>>> Oh my comment was pretty much just bikeshed, in case someone creates a
> >>>>>>>> $REGION that other drivers use for $CATEGORY. Kinda Rob's parsing point.
> >>>>>>>> So $CATEGORY before the -memory.
> >>>>>>>>
> >>>>>>>> Otoh I don't think that'll happen, so I guess we can go with whatever more
> >>>>>>>> folks like :-) I don't really care much personally.
> >>>>>>>
> >>>>>>> Okay I missed the parsing problem.
> >>>>>>>
> >>>>>>>>> AMD currently has (among others) drm-memory-vram, which we could define in
> >>>>>>>>> the spec maps to category X, if category component is not present.
> >>>>>>>>>
> >>>>>>>>> Some examples:
> >>>>>>>>>
> >>>>>>>>> drm-memory-resident-system:
> >>>>>>>>> drm-memory-size-lmem0:
> >>>>>>>>> drm-memory-active-vram:
> >>>>>>>>>
> >>>>>>>>> Etc.. I think it creates a consistent story.
> >>>>>>>>>
> >>>>>>>>> Other than this, my two I think significant opens which haven't been
> >>>>>>>>> addressed yet are:
> >>>>>>>>>
> >>>>>>>>> 1)
> >>>>>>>>>
> >>>>>>>>> Why do we want totals (not per region) when userspace can trivially
> >>>>>>>>> aggregate if they want. What is the use case?
> >>>>>>>>>
> >>>>>>>>> 2)
> >>>>>>>>>
> >>>>>>>>> Current proposal limits the value to whole objects and fixates that by
> >>>>>>>>> having it in the common code. If/when some driver is able to support sub-BO
> >>>>>>>>> granularity they will need to opt out of the common printer at which point
> >>>>>>>>> it may be less churn to start with a helper rather than mid-layer. Or maybe
> >>>>>>>>> some drivers already support this, I don't know. Given how important VM BIND
> >>>>>>>>> is I wouldn't be surprised.
> >>>>>>>>
> >>>>>>>> I feel like for drivers using ttm we want a ttm helper which takes care of
> >>>>>>>> the region printing in hopefully a standard way. And that could then also
> >>>>>>>> take care of all kinds of of partial binding and funny rules (like maybe
> >>>>>>>> we want a standard vram region that addds up all the lmem regions on
> >>>>>>>> intel, so that all dgpu have a common vram bucket that generic tools
> >>>>>>>> understand?).
> >>>>>>>
> >>>>>>> First part yes, but for the second I would think we want to avoid any
> >>>>>>> aggregation in the kernel which can be done in userspace just as well. Such
> >>>>>>> total vram bucket would be pretty useless on Intel even since userspace
> >>>>>>> needs to be region aware to make use of all resources. It could even be
> >>>>>>> counter productive I think - "why am I getting out of memory when half of my
> >>>>>>> vram is unused!?".
> >>>>>>
> >>>>>> This is not for intel-aware userspace. This is for fairly generic "gputop"
> >>>>>> style userspace, which might simply have no clue or interest in what lmemX
> >>>>>> means, but would understand vram.
> >>>>>>
> >>>>>> Aggregating makes sense.
> >>>>>
> >>>>> Lmem vs vram is now an argument not about aggregation but about
> >>>>> standardizing regions names.
> >>>>>
> >>>>> One detail also is a change in philosophy compared to engine stats where
> >>>>> engine names are not centrally prescribed and it was expected userspace
> >>>>> will have to handle things generically and with some vendor specific
> >>>>> knowledge.
> >>>>>
> >>>>> Like in my gputop patches. It doesn't need to understand what is what,
> >>>>> it just finds what's there and presents it to the user.
> >>>>>
> >>>>> Come some accel driver with local memory it wouldn't be vram any more.
> >>>>> Or even a headless data center GPU. So I really don't think it is good
> >>>>> to hardcode 'vram' in the spec, or midlayer, or helpers.
> >>>>>
> >>>>> And for aggregation.. again, userspace can do it just as well. If we do
> >>>>> it in kernel then immediately we have multiple sets of keys to output
> >>>>> for any driver which wants to show the region view. IMO it is just
> >>>>> pointless work in the kernel and more code in the kernel, when userspace
> >>>>> can do it.
> >>>>>
> >>>>> Proposal A (one a discrete gpu, one category only):
> >>>>>
> >>>>> drm-resident-memory: x KiB
> >>>>> drm-resident-memory-system: x KiB
> >>>>> drm-resident-memory-vram: x KiB
> >>>>>
> >>>>> Two loops in the kernel, more parsing in userspace.
> >>>>
> >>>> why would it be more than one loop, ie.
> >>>>
> >>>>       mem.resident += size;
> >>>>       mem.category[cat].resident += size;
> >>>>
> >>>> At the end of the day, there is limited real-estate to show a million
> >>>> different columns of information.  Even the gputop patches I posted
> >>>> don't show everything of what is currently there.  And nvtop only
> >>>> shows toplevel resident stat.  So I think the "everything" stat is
> >>>> going to be what most tools use.
> >>>
> >>> Yeah with enough finesse the double-loop isn't needed, it's just the
> >>> simplest possible approach.
> >>>
> >>> Also this is fdinfo, I _really_ want perf data showing that it's a
> >>> real-world problem when we conjecture about algorithmic complexity.
> >>> procutils have been algorithmically garbage since decades after all :-)
> >>
> >> Just run it. :)
> >>
> >> Algorithmic complexity is quite obvious and not a conjecture - to find
> >> DRM clients you have to walk _all_ pids and _all_ fds under them. So
> >> amount of work can scale very quickly and even _not_ with the number of
> >> DRM clients.
> >>
> >> It's not too bad on my desktop setup but it is significantly more CPU
> >> intensive than top(1).
> >>
> >> It would be possible to optimise the current code some more by not
> >> parsing full fdinfo (may become more important as number of keys grow),
> >> but that's only relevant when number of drm fds is large. It doesn't
> >> solve the basic pids * open fds search for which we'd need a way to walk
> >> the list of pids with drm fds directly.
> >
> > All of which has (almost[1]) nothing to do with one loop or two
>
> Correct, this was just a side discussion where I understood Daniel is
> asking about the wider performance story. Perhaps I misunderstood.
>
> > (ignoring for a moment that I already pointed out a single loop is all
> > that is needed).  If CPU overhead is a problem, we could perhaps come
> > up some sysfs which has one file per drm_file and side-step crawling
> > of all of the proc * fd.  I'll play around with it some but I'm pretty
> > sure you are trying to optimize the wrong thing.
>
> Yes, that's what I meant too in "a way to walk the list of pids with drm
> fds directly".

Just to follow up, I did a quick hack to loop and print the mem
stats.. 5x loops I couldn't really measure any increase in gputop CPU
utilization.  At 50x loops I could measure a small increase.  Without
additional looping to artificially increase the cost, nothing drm
related shows up in a perf-record of gputop.

What could be an easy optimization, if it can be accessed, is to parse
/sys/kernel/debug/dri/<n>/clients to get the list of pid's of
processes with the drm device open.  This would cut down quite a bit
the # of pid's to examine.

BR,
-R

> Regards,
>
> Tvrtko
>
> >
> > BR,
> > -R
> >
> > [1] generally a single process using drm has multiple fd's pointing at
> > the same drm_file.. which makes the current approach of having to read
> > fdinfo to find the client-id sub-optimal.  But still the total # of
> > proc * fd is much larger