• Tvrtko Ursulin's avatar
    drm/i915: Emit to ringbuffer directly · 73dec95e
    Tvrtko Ursulin authored
    This removes the usage of intel_ring_emit in favour of
    directly writing to the ring buffer.
    
    intel_ring_emit was preventing the compiler for optimising
    fetch and increment of the current ring buffer pointer and
    therefore generating very verbose code for every write.
    
    It had no useful purpose since all ringbuffer operations
    are started and ended with intel_ring_begin and
    intel_ring_advance respectively, with no bail out in the
    middle possible, so it is fine to increment the tail in
    intel_ring_begin and let the code manage the pointer
    itself.
    
    Useless instruction removal amounts to approximately
    two and half kilobytes of saved text on my build.
    
    Not sure if this has any measurable performance
    implications but executing a ton of useless instructions
    on fast paths cannot be good.
    
    v2:
     * Change return from intel_ring_begin to error pointer by
       popular demand.
     * Move tail increment to intel_ring_advance to enable some
       error checking.
    
    v3:
     * Move tail advance back into intel_ring_begin.
     * Rebase and tidy.
    
    v4:
     * Complete rebase after a few months since v3.
    
    v5:
     * Remove unecessary cast and fix !debug compile. (Chris Wilson)
    
    v6:
     * Make intel_ring_offset take request as well.
     * Fix recording of request postfix plus a sprinkle of asserts.
       (Chris Wilson)
    
    v7:
     * Use intel_ring_offset to get the postfix. (Chris Wilson)
     * Convert GVT code as well.
    
    v8:
     * Rename *out++ to *cs++.
    
    v9:
     * Fix GVT out to cs conversion in GVT.
    
    v10:
     * Rebase for new intel_ring_begin in selftests.
    Signed-off-by: default avatarTvrtko Ursulin <tvrtko.ursulin@intel.com>
    Cc: Chris Wilson <chris@chris-wilson.co.uk>
    Cc: Joonas Lahtinen <joonas.lahtinen@linux.intel.com>
    Cc: Zhi Wang <zhi.a.wang@intel.com>
    Reviewed-by: default avatarChris Wilson <chris@chris-wilson.co.uk>
    Acked-by: default avatarJoonas Lahtinen <joonas.lahtinen@linux.intel.com>
    Link: http://patchwork.freedesktop.org/patch/msgid/20170214113242.29241-1-tvrtko.ursulin@linux.intel.com
    73dec95e
intel_ringbuffer.h 21.6 KB