• Chris Wilson's avatar
    drm/i915: Keep contexts pinned until after the next kernel context switch · ce476c80
    Chris Wilson authored
    We need to keep the context image pinned in memory until after the GPU
    has finished writing into it. Since it continues to write as we signal
    the final breadcrumb, we need to keep it pinned until the request after
    it is complete. Currently we know the order in which requests execute on
    each engine, and so to remove that presumption we need to identify a
    request/context-switch we know must occur after our completion. Any
    request queued after the signal must imply a context switch, for
    simplicity we use a fresh request from the kernel context.
    
    The sequence of operations for keeping the context pinned until saved is:
    
     - On context activation, we preallocate a node for each physical engine
       the context may operate on. This is to avoid allocations during
       unpinning, which may be from inside FS_RECLAIM context (aka the
       shrinker)
    
     - On context deactivation on retirement of the last active request (which
       is before we know the context has been saved), we add the
       preallocated node onto a barrier list on each engine
    
     - On engine idling, we emit a switch to kernel context. When this
       switch completes, we know that all previous contexts must have been
       saved, and so on retiring this request we can finally unpin all the
       contexts that were marked as deactivated prior to the switch.
    
    We can enhance this in future by flushing all the idle contexts on a
    regular heartbeat pulse of a switch to kernel context, which will also
    be used to check for hung engines.
    
    v2: intel_context_active_acquire/_release
    Signed-off-by: default avatarChris Wilson <chris@chris-wilson.co.uk>
    Cc: Mika Kuoppala <mika.kuoppala@linux.intel.com>
    Reviewed-by: default avatarMika Kuoppala <mika.kuoppala@linux.intel.com>
    Link: https://patchwork.freedesktop.org/patch/msgid/20190614164606.15633-1-chris@chris-wilson.co.uk
    ce476c80
intel_lrc.c 104 KB