[Bug 107403] Quadratic behavior due to leaking fence contexts in reservation objects

[bugzilla-daemon@freedesktop.org]

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https://bugs.freedesktop.org/show_bug.cgi?id=107403

            Bug ID: 107403
           Summary: Quadratic behavior due to leaking fence contexts in
                    reservation objects
           Product: DRI
           Version: XOrg git
          Hardware: Other
                OS: All
            Status: NEW
          Severity: normal
          Priority: medium
         Component: DRM/AMDgpu
          Assignee: dri-devel@lists.freedesktop.org
          Reporter: bas@basnieuwenhuizen.nl

As part of the Vulkan CTS, radv creates about 30k AMDGPU contexts (about 1-20
live at the same time though).

Each of those creates a bunch of fence contexts, one for each ring, to use for
fences created from submitted jobs.

However, as part of running jobs, fences with those contexts get attached to
the
vm->root.base.bo->tbo.resv of the corresponding vm. Which means that at some
point we have tens of thousands of fences attached to it as they never get
removed. They only ever get deduplicated with a later fence from the same fence
context, so fences from destroyed contexts never get removed.

Then in amdgpu_gem_va_ioctl -> amdgpu_vm_clear_freed ->
amdgpu_vm_bo_update_mapping we do an amdgpu_sync_resv, which tries to add that
to an amdgpu_sync object. Which only has a 16-entry hashtable, so adding the
fences to the hashtable results in quadratic behavior.

Combine this with doing sparse buffer tests at the end, which do lots of VA
operations this results in tests taking 20+ minuts.

So I could reduce the number of amdgpu contexts a bit in radv, but the bigger
issue in my opnion is that we are pretty much leaking and never reclaiming the
fences.

Any idea how to best remove some signalled fences?

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