drivers/gpu/drm/i915/gem/i915_gem_throttle.c

   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 i915_gem_throttle_ioctl(struct drm_device *dev, void *data,
  36                         struct drm_file *file)
  37 {
  38         struct drm_i915_file_private *file_priv = file->driver_priv;
  39         unsigned long recent_enough = jiffies - DRM_I915_THROTTLE_JIFFIES;
  40         struct i915_request *request, *target = NULL;
  41         long ret;
  42
  43         /* ABI: return -EIO if already wedged */
  44         ret = intel_gt_terminally_wedged(&to_i915(dev)->gt);
  45         if (ret)
  46                 return ret;
  47
  48         spin_lock(&file_priv->mm.lock);
  49         list_for_each_entry(request, &file_priv->mm.request_list, client_link) {
  50                 if (time_after_eq(request->emitted_jiffies, recent_enough))
  51                         break;
  52
  53                 if (target && xchg(&target->file_priv, NULL))
  54                         list_del(&target->client_link);
  55
  56                 target = request;
  57         }
  58         if (target)
  59                 i915_request_get(target);
  60         spin_unlock(&file_priv->mm.lock);
  61
  62         if (!target)
  63                 return 0;
  64
  65         ret = i915_request_wait(target,
  66                                 I915_WAIT_INTERRUPTIBLE,
  67                                 MAX_SCHEDULE_TIMEOUT);
  68         i915_request_put(target);
  69
  70         return ret < 0 ? ret : 0;
  71 }