Re: [RFC PATCH 5/7] drm/ttm: add range busy check for range manager

[Robert Beckett]

On 16/03/2022 13:43, Christian König wrote:
> Am 16.03.22 um 14:19 schrieb Robert Beckett:
> > On 16/03/2022 09:54, Christian König wrote:
> > > Am 15.03.22 um 19:04 schrieb Robert Beckett:
> > > > RFC: do we want this to become a generic interface in
> > > > ttm_resource_manager_func?
> > > >
> > > > RFC: would we prefer a different interface? e.g.
> > > > for_each_resource_in_range or for_each_bo_in_range
> > >
> > > Well completely NAK to that. Why do you need that?
> > >
> > > The long term goal is to completely remove the range checks from TTM 
> > > instead.
> >
> > ah, I did not know that.
> > I wanted it just to enable parity with a selftest that checks whether 
> > a range is allocated before initializing a given range with test data 
> > behind the allocator's back. It needs to check the range so that it 
> > doesn't destroy in use data.
>
> Mhm, of hand that doesn't sounds like a valid test case. Do you have the 
> code at hand?

https://patchwork.freedesktop.org/patch/478347/?series=101396&rev=1
this is where I replace an existing range check via drm_mm with the 
range check I added in this patch.

> > I suppose we could add another drm_mm range tracker just for testing 
> > and shadow track each allocation in the range, but that seemed like a 
> > lot of extra infrastructure for no general runtime use.
>
> I have no idea what you mean with that.

I meant as a potential solution to tracking allocations without a range 
check, we would need to add something external. e.g. adding a shadow 
drm_mm range tracker, or a bitmask across the range, or stick objects in 
a list etc.

> > would you mind explaining the rationale for removing range checks? It 
> > seems to me like a natural fit for a memory manager
>
> TTM manages buffer objects and resources, not address space. The 
> lpfn/fpfn parameter for the resource allocators are actually used as 
> just two independent parameters and not define any range. We just keep 
> the names for historical reasons.
>
> The only places we still use and compare them as ranges are 
> ttm_resource_compat() and ttm_bo_eviction_valuable() and I already have 
> patches to clean up those and move them into the backend resource handling.

except the ttm_range_manager seems to still use them as a range specifier.

If the general design going forward is to not consider ranges, how would 
you recommend constructing buffers around pre-allocated regions e.g. 
uefi frame buffers who's range is dictated externally?

> Regards,
> Christian.
>
> > > Regards,
> > > Christian.
> > >
> > > > Signed-off-by: Robert Beckett <bob.beckett@xxxxxxxxxxxxx>
> > > > ---
> > > >   drivers/gpu/drm/ttm/ttm_range_manager.c | 21 +++++++++++++++++++++
> > > >   include/drm/ttm/ttm_range_manager.h     |  3 +++
> > > >   2 files changed, 24 insertions(+)
> > > >
> > > > diff --git a/drivers/gpu/drm/ttm/ttm_range_manager.c 
> > > > b/drivers/gpu/drm/ttm/ttm_range_manager.c
> > > > index 8cd4f3fb9f79..5662627bb933 100644
> > > > --- a/drivers/gpu/drm/ttm/ttm_range_manager.c
> > > > +++ b/drivers/gpu/drm/ttm/ttm_range_manager.c
> > > > @@ -206,3 +206,24 @@ int ttm_range_man_fini_nocheck(struct 
> > > > ttm_device *bdev,
> > > >       return 0;
> > > >   }
> > > >   EXPORT_SYMBOL(ttm_range_man_fini_nocheck);
> > > > +
> > > > +/**
> > > > + * ttm_range_man_range_busy - Check whether anything is allocated 
> > > > with a range
> > > > + *
> > > > + * @man: memory manager to check
> > > > + * @fpfn: first page number to check
> > > > + * @lpfn: last page number to check
> > > > + *
> > > > + * Return: true if anything allocated within the range, false 
> > > > otherwise.
> > > > + */
> > > > +bool ttm_range_man_range_busy(struct ttm_resource_manager *man,
> > > > +                  unsigned fpfn, unsigned lpfn)
> > > > +{
> > > > +    struct ttm_range_manager *rman = to_range_manager(man);
> > > > +    struct drm_mm *mm = &rman->mm;
> > > > +
> > > > +    if (__drm_mm_interval_first(mm, PFN_PHYS(fpfn), PFN_PHYS(lpfn + 
> > > > 1) - 1))
> > > > +        return true;
> > > > +    return false;
> > > > +}
> > > > +EXPORT_SYMBOL(ttm_range_man_range_busy);
> > > > diff --git a/include/drm/ttm/ttm_range_manager.h 
> > > > b/include/drm/ttm/ttm_range_manager.h
> > > > index 7963b957e9ef..86794a3f9101 100644
> > > > --- a/include/drm/ttm/ttm_range_manager.h
> > > > +++ b/include/drm/ttm/ttm_range_manager.h
> > > > @@ -53,4 +53,7 @@ static __always_inline int 
> > > > ttm_range_man_fini(struct ttm_device *bdev,
> > > >       BUILD_BUG_ON(__builtin_constant_p(type) && type >= 
> > > > TTM_NUM_MEM_TYPES);
> > > >       return ttm_range_man_fini_nocheck(bdev, type);
> > > >   }
> > > > +
> > > > +bool ttm_range_man_range_busy(struct ttm_resource_manager *man,
> > > > +                  unsigned fpfn, unsigned lpfn);
> > > >   #endif