• Chris Wilson's avatar
    drm/i915: Invert the GEM wakeref hierarchy · 79ffac85
    Chris Wilson authored
    In the current scheme, on submitting a request we take a single global
    GEM wakeref, which trickles down to wake up all GT power domains. This
    is undesirable as we would like to be able to localise our power
    management to the available power domains and to remove the global GEM
    operations from the heart of the driver. (The intent there is to push
    global GEM decisions to the boundary as used by the GEM user interface.)
    
    Now during request construction, each request is responsible via its
    logical context to acquire a wakeref on each power domain it intends to
    utilize. Currently, each request takes a wakeref on the engine(s) and
    the engines themselves take a chipset wakeref. This gives us a
    transition on each engine which we can extend if we want to insert more
    powermangement control (such as soft rc6). The global GEM operations
    that currently require a struct_mutex are reduced to listening to pm
    events from the chipset GT wakeref. As we reduce the struct_mutex
    requirement, these listeners should evaporate.
    
    Perhaps the biggest immediate change is that this removes the
    struct_mutex requirement around GT power management, allowing us greater
    flexibility in request construction. Another important knock-on effect,
    is that by tracking engine usage, we can insert a switch back to the
    kernel context on that engine immediately, avoiding any extra delay or
    inserting global synchronisation barriers. This makes tracking when an
    engine and its associated contexts are idle much easier -- important for
    when we forgo our assumed execution ordering and need idle barriers to
    unpin used contexts. In the process, it means we remove a large chunk of
    code whose only purpose was to switch back to the kernel context.
    Signed-off-by: default avatarChris Wilson <chris@chris-wilson.co.uk>
    Cc: Tvrtko Ursulin <tvrtko.ursulin@intel.com>
    Cc: Imre Deak <imre.deak@intel.com>
    Reviewed-by: default avatarTvrtko Ursulin <tvrtko.ursulin@intel.com>
    Link: https://patchwork.freedesktop.org/patch/msgid/20190424200717.1686-5-chris@chris-wilson.co.uk
    79ffac85
intel_ringbuffer.c 59.7 KB