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

Rob Clark
2023-04-14T13:40:53Z

On Fri, Apr 14, 2023 at 1:57 AM Tvrtko Ursulin
<tvrtko.ursulin@linux.intel.com> 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@ffwll.ch> 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@linux.intel.com> wrote:
> >>>>>>>>>
> >>>>>>>>>
> >>>>>>>>> On 11/04/2023 23:56, Rob Clark wrote:
> >>>>>>>>>> From: Rob Clark <robdclark@chromium.org>
> >>>>>>>>>>
> >>>>>>>>>> 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@chromium.org>
> >>>>>>>>>> Reviewed-by: Emil Velikov <emil.l.velikov@gmail.com>
> >>>>>>>>>> ---
> >>>>>>>>>> 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.

BR,
-R

> Proposal B:
>
> drm-resident-memory-system: x KiB
> drm-resident-memory-vram: x KiB
>
> Can be one loop, one helper, less text for userspace to parse and it can
> still trivially show the total if so desired.
>
> For instance a helper (or two) with a common struct containing region
> names and totals, where a callback into the driver tallies under each
> region, as the drm helper is walking objects.
>
> >>> It does mean we walk the bo list twice, but *shrug*. People have been
> >>> complaining about procutils for decades, they're still horrible, I think
> >>> walking bo lists twice internally in the ttm case is going to be ok. If
> >>> not, it's internals, we can change them again.
> >>>
> >>> Also I'd lean a lot more towards making ttm a helper and not putting that
> >>> into core, exactly because it's pretty clear we'll need more flexibility
> >>> when it comes to accurate stats for multi-region drivers.
> >>
> >> Exactly.
> >>
> >>> But for a first "how much gpu space does this app use" across everything I
> >>> think this is a good enough starting point.
> >>
> >> Okay so we agree this would be better as a helper and not in the core.
> >
> > Nope, if you mean with this = Rob's patch. I was talking about a
> > hypothetical region-aware extension for ttm-using drivers.
> >
> >> On the point are keys/semantics good enough as a starting point I am still
> >> not convinced kernel should aggregate and that instead we should start from
> >> day one by appending -system (or something) to Rob's proposed keys.
> >
> > It should imo. Inflicting driver knowledge on generic userspace makes not
> > much sense, we should start with the more generally useful stuff imo.
> > That's why there's the drm fdinfo spec and all that so it's not a
> > free-for-all.
> >
> > Also Rob's stuff is _not_ system. Check on a i915 dgpu if you want :-)
>
> I am well aware it adds up everything, that is beside the point.
>
> Drm-usage-stats.rst text needs to be more precise across all keys at least:
>
> +- drm-resident-memory: <uint> [KiB|MiB]
> +
> +The total size of buffers that are resident in system memory.
>
> But as said, I don't see the point in providing aggregated values.
>
> Regards,
>
> Tvrtko