[Intel-gfx] [PATCH] drm: Return current vblank value for drmWaitVBlank queries

[Chris Wilson]

On Thu, Mar 19, 2015 at 03:13:15PM +0000, Chris Wilson wrote:
> Pretty much an igt that compared the speed of just querying the hw
> counter vs querying with a regular vblank interrupt would be ideal for
> measuring the impact here.

ickle at crystalwell:/usr/src/intel-gpu-tools$ sudo ./tests/kms_vblank 
IGT-Version: 1.10-gc15fb9e (x86_64) (Linux: 4.0.0-rc4+ x86_64)
Time to query current counter (idle):		  2.217µs
Subtest query-idle: SUCCESS (1.006s)
Time to query current counter (busy):		  0.244µs
Subtest query-busy: SUCCESS (1.201s

-  28.04%     kms_vblank  [kernel.kallsyms]   [k] gen6_read32                  
   - gen6_read32                                                               
      + 65.27% gm45_get_vblank_counter                                         
      + 17.50% ironlake_disable_display_irq                                    
      + 16.53% ironlake_enable_display_irq                                     
+  21.57%     kms_vblank  [kernel.kallsyms]   [k] hsw_unclaimed_reg_detect.isra
+  10.69%     kms_vblank  [kernel.kallsyms]   [k] _raw_spin_lock_irqsave       
+   9.91%     kms_vblank  [kernel.kallsyms]   [k] __intel_get_crtc_scanline    
+   6.66%     kms_vblank  [kernel.kallsyms]   [k] _raw_spin_unlock_irqrestore 
+   1.34%     kms_vblank  [kernel.kallsyms]   [k] i915_get_crtc_scanoutpos     
+   1.29%     kms_vblank  [kernel.kallsyms]   [k] drm_wait_vblank              
+   1.27%     kms_vblank  [kernel.kallsyms]   [k] hsw_unclaimed_reg_debug.isra.
+   1.17%     kms_vblank  [kernel.kallsyms]   [k] copy_user_enhanced_fast_strin
+   1.12%     kms_vblank  [kernel.kallsyms]   [k] drm_ioctl                    
+   1.05%     kms_vblank  [kernel.kallsyms]   [k] vblank_disable_and_save 

-- 
Chris Wilson, Intel Open Source Technology Centre