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By recording the location of every request in the ringbuffer, we know that in order to retire the request the GPU must have finished reading it and so the GPU head is now beyond the tail of the request. We can therefore provide a conservative estimate of where the GPU is reading from in order to avoid having to read back the ring buffer registers when polling for space upon starting a new write into the ringbuffer. A secondary effect is that this allows us to convert intel_ring_buffer_wait() to use i915_wait_request() and so consolidate upon the single function to handle the complicated task of waiting upon the GPU. A necessary precaution is that we need to make that wait uninterruptible to match the existing conditions as all the callers of intel_ring_begin() have not been audited to handle ERESTARTSYS correctly. By using a conservative estimate for the head, and always processing all outstanding requests first, we prevent a race condition between using the estimate and direct reads of I915_RING_HEAD which could result in the value of the head going backwards, and the tail overflowing once again. We are also careful to mark any request that we skip over in order to free space in ring as consumed which provides a self-consistency check. Given sufficient abuse, such as a set of unthrottled GPU bound cairo-traces, avoiding the use of I915_RING_HEAD gives a 10-20% boost on Sandy Bridge (i5-2520m): firefox-paintball 18927ms -> 15646ms: 1.21x speedup firefox-fishtank 12563ms -> 11278ms: 1.11x speedup which is a mild consolation for the performance those traces achieved from exploiting the buggy autoreported head. v2: Add a few more comments and make request->tail a conservative estimate as suggested by Daniel Vetter. Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk> [danvet: resolve conflicts with retirement defering and the lack of the autoreport head removal (that will go in through -fixes).] Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch> |
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| .. | ||
| dvo_ch7xxx.c | ||
| dvo_ch7017.c | ||
| dvo_ivch.c | ||
| dvo_sil164.c | ||
| dvo_tfp410.c | ||
| dvo.h | ||
| i915_debugfs.c | ||
| i915_dma.c | ||
| i915_drv.c | ||
| i915_drv.h | ||
| i915_gem_debug.c | ||
| i915_gem_evict.c | ||
| i915_gem_execbuffer.c | ||
| i915_gem_gtt.c | ||
| i915_gem_tiling.c | ||
| i915_gem.c | ||
| i915_ioc32.c | ||
| i915_irq.c | ||
| i915_reg.h | ||
| i915_suspend.c | ||
| i915_trace_points.c | ||
| i915_trace.h | ||
| intel_acpi.c | ||
| intel_bios.c | ||
| intel_bios.h | ||
| intel_crt.c | ||
| intel_display.c | ||
| intel_dp.c | ||
| intel_drv.h | ||
| intel_dvo.c | ||
| intel_fb.c | ||
| intel_hdmi.c | ||
| intel_i2c.c | ||
| intel_lvds.c | ||
| intel_modes.c | ||
| intel_opregion.c | ||
| intel_overlay.c | ||
| intel_panel.c | ||
| intel_ringbuffer.c | ||
| intel_ringbuffer.h | ||
| intel_sdvo_regs.h | ||
| intel_sdvo.c | ||
| intel_sprite.c | ||
| intel_tv.c | ||
| Makefile | ||