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       1                 :            : /*
       2                 :            :  * SPDX-License-Identifier: MIT
       3                 :            :  *
       4                 :            :  * Copyright © 2014-2016 Intel Corporation
       5                 :            :  */
       6                 :            : 
       7                 :            : #include <linux/jiffies.h>
       8                 :            : 
       9                 :            : #include <drm/drm_file.h>
      10                 :            : 
      11                 :            : #include "i915_drv.h"
      12                 :            : #include "i915_gem_ioctls.h"
      13                 :            : #include "i915_gem_object.h"
      14                 :            : 
      15                 :            : /*
      16                 :            :  * 20ms is a fairly arbitrary limit (greater than the average frame time)
      17                 :            :  * chosen to prevent the CPU getting more than a frame ahead of the GPU
      18                 :            :  * (when using lax throttling for the frontbuffer). We also use it to
      19                 :            :  * offer free GPU waitboosts for severely congested workloads.
      20                 :            :  */
      21                 :            : #define DRM_I915_THROTTLE_JIFFIES msecs_to_jiffies(20)
      22                 :            : 
      23                 :            : /*
      24                 :            :  * Throttle our rendering by waiting until the ring has completed our requests
      25                 :            :  * emitted over 20 msec ago.
      26                 :            :  *
      27                 :            :  * Note that if we were to use the current jiffies each time around the loop,
      28                 :            :  * we wouldn't escape the function with any frames outstanding if the time to
      29                 :            :  * render a frame was over 20ms.
      30                 :            :  *
      31                 :            :  * This should get us reasonable parallelism between CPU and GPU but also
      32                 :            :  * relatively low latency when blocking on a particular request to finish.
      33                 :            :  */
      34                 :            : int
      35                 :          0 : i915_gem_throttle_ioctl(struct drm_device *dev, void *data,
      36                 :            :                         struct drm_file *file)
      37                 :            : {
      38                 :          0 :         struct drm_i915_file_private *file_priv = file->driver_priv;
      39                 :          0 :         unsigned long recent_enough = jiffies - DRM_I915_THROTTLE_JIFFIES;
      40                 :          0 :         struct i915_request *request, *target = NULL;
      41                 :          0 :         long ret;
      42                 :            : 
      43                 :            :         /* ABI: return -EIO if already wedged */
      44                 :          0 :         ret = intel_gt_terminally_wedged(&to_i915(dev)->gt);
      45         [ #  # ]:          0 :         if (ret)
      46                 :            :                 return ret;
      47                 :            : 
      48                 :          0 :         spin_lock(&file_priv->mm.lock);
      49         [ #  # ]:          0 :         list_for_each_entry(request, &file_priv->mm.request_list, client_link) {
      50         [ #  # ]:          0 :                 if (time_after_eq(request->emitted_jiffies, recent_enough))
      51                 :            :                         break;
      52                 :            : 
      53   [ #  #  #  # ]:          0 :                 if (target && xchg(&target->file_priv, NULL))
      54                 :          0 :                         list_del(&target->client_link);
      55                 :            : 
      56                 :          0 :                 target = request;
      57                 :            :         }
      58         [ #  # ]:          0 :         if (target)
      59         [ #  # ]:          0 :                 i915_request_get(target);
      60                 :          0 :         spin_unlock(&file_priv->mm.lock);
      61                 :            : 
      62         [ #  # ]:          0 :         if (!target)
      63                 :            :                 return 0;
      64                 :            : 
      65                 :          0 :         ret = i915_request_wait(target,
      66                 :            :                                 I915_WAIT_INTERRUPTIBLE,
      67                 :            :                                 MAX_SCHEDULE_TIMEOUT);
      68                 :          0 :         i915_request_put(target);
      69                 :            : 
      70                 :          0 :         return ret < 0 ? ret : 0;
      71                 :            : }