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| author | Joonas Lahtinen <joonas.lahtinen@linux.intel.com> | 2019-08-30 13:50:53 +0300 |
|---|---|---|
| committer | Joonas Lahtinen <joonas.lahtinen@linux.intel.com> | 2020-05-14 20:24:54 +0300 |
| commit | ca69a3c68e2150ffb73ff1ff7d2b5390d76b3eb9 (patch) | |
| tree | 0fc2a902104931c89c118ab0be3ee2e9d19e412e /Documentation/gpu | |
| parent | 802a5820fc0c0f12b40280db3dbaaf8359b07243 (diff) | |
| download | linux-ca69a3c68e2150ffb73ff1ff7d2b5390d76b3eb9.tar.xz | |
drm/i915: Document locking guidelines
To ensure cross-driver locking compatibility, document the expected
guidelines for implementing the GEM locking in i915. Note that this
is a description of how things should end up after being reworked,
and does not reflect the current state of things.
v2: Use rst note:: tag (Rodrigo)
Signed-off-by: Joonas Lahtinen <joonas.lahtinen@linux.intel.com>
Signed-off-by: Daniel Vetter <daniel.vetter@intel.com>
Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
Cc: Dave Airlie <airlied@redhat.com>
Cc: Matthew Auld <matthew.auld@intel.com>
Cc: Abdiel Janulgue <abdiel.janulgue@linux.intel.com>
Cc: CQ Tang <cq.tang@intel.com>
Reviewed-by: Rodrigo Vivi <rodrigo.vivi@intel.com>
Acked-by: Dave Airlie <airlied@redhat.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20190830105053.17491-1-joonas.lahtinen@linux.intel.com
Diffstat (limited to 'Documentation/gpu')
| -rw-r--r-- | Documentation/gpu/i915.rst | 46 |
1 files changed, 46 insertions, 0 deletions
diff --git a/Documentation/gpu/i915.rst b/Documentation/gpu/i915.rst index 429b08aac797..33cc6ddf8f64 100644 --- a/Documentation/gpu/i915.rst +++ b/Documentation/gpu/i915.rst @@ -329,6 +329,52 @@ for execution also include a list of all locations within buffers that refer to GPU-addresses so that the kernel can edit the buffer correctly. This process is dubbed relocation. +Locking Guidelines +------------------ + +.. note:: + This is a description of how the locking should be after + refactoring is done. Does not necessarily reflect what the locking + looks like while WIP. + +#. All locking rules and interface contracts with cross-driver interfaces + (dma-buf, dma_fence) need to be followed. + +#. No struct_mutex anywhere in the code + +#. dma_resv will be the outermost lock (when needed) and ww_acquire_ctx + is to be hoisted at highest level and passed down within i915_gem_ctx + in the call chain + +#. While holding lru/memory manager (buddy, drm_mm, whatever) locks + system memory allocations are not allowed + + * Enforce this by priming lockdep (with fs_reclaim). If we + allocate memory while holding these looks we get a rehash + of the shrinker vs. struct_mutex saga, and that would be + real bad. + +#. Do not nest different lru/memory manager locks within each other. + Take them in turn to update memory allocations, relying on the object’s + dma_resv ww_mutex to serialize against other operations. + +#. The suggestion for lru/memory managers locks is that they are small + enough to be spinlocks. + +#. All features need to come with exhaustive kernel selftests and/or + IGT tests when appropriate + +#. All LMEM uAPI paths need to be fully restartable (_interruptible() + for all locks/waits/sleeps) + + * Error handling validation through signal injection. + Still the best strategy we have for validating GEM uAPI + corner cases. + Must be excessively used in the IGT, and we need to check + that we really have full path coverage of all error cases. + + * -EDEADLK handling with ww_mutex + GEM BO Management Implementation Details ---------------------------------------- |