• Chris Wilson's avatar
    drm/i915: Coordinate i915_active with its own mutex · b1e3177b
    Chris Wilson authored
    Forgo the struct_mutex serialisation for i915_active, and interpose its
    own mutex handling for active/retire.
    
    This is a multi-layered sleight-of-hand. First, we had to ensure that no
    active/retire callbacks accidentally inverted the mutex ordering rules,
    nor assumed that they were themselves serialised by struct_mutex. More
    challenging though, is the rule over updating elements of the active
    rbtree. Instead of the whole i915_active now being serialised by
    struct_mutex, allocations/rotations of the tree are serialised by the
    i915_active.mutex and individual nodes are serialised by the caller
    using the i915_timeline.mutex (we need to use nested spinlocks to
    interact with the dma_fence callback lists).
    
    The pain point here is that instead of a single mutex around execbuf, we
    now have to take a mutex for active tracker (one for each vma, context,
    etc) and a couple of spinlocks for each fence update. The improvement in
    fine grained locking allowing for multiple concurrent clients
    (eventually!) should be worth it in typical loads.
    
    v2: Add some comments that barely elucidate anything :(
    Signed-off-by: default avatarChris Wilson <chris@chris-wilson.co.uk>
    Reviewed-by: default avatarTvrtko Ursulin <tvrtko.ursulin@intel.com>
    Link: https://patchwork.freedesktop.org/patch/msgid/20191004134015.13204-6-chris@chris-wilson.co.uk
    b1e3177b
selftest_context.c 9.89 KB