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      1 /*	$NetBSD: i915_gem_throttle.c,v 1.2 2021/12/18 23:45:30 riastradh Exp $	*/
      2 
      3 /*
      4  * SPDX-License-Identifier: MIT
      5  *
      6  * Copyright  2014-2016 Intel Corporation
      7  */
      8 
      9 #include <sys/cdefs.h>
     10 __KERNEL_RCSID(0, "$NetBSD: i915_gem_throttle.c,v 1.2 2021/12/18 23:45:30 riastradh Exp $");
     11 
     12 #include <linux/jiffies.h>
     13 
     14 #include <drm/drm_file.h>
     15 
     16 #include "i915_drv.h"
     17 #include "i915_gem_ioctls.h"
     18 #include "i915_gem_object.h"
     19 
     20 /*
     21  * 20ms is a fairly arbitrary limit (greater than the average frame time)
     22  * chosen to prevent the CPU getting more than a frame ahead of the GPU
     23  * (when using lax throttling for the frontbuffer). We also use it to
     24  * offer free GPU waitboosts for severely congested workloads.
     25  */
     26 #define DRM_I915_THROTTLE_JIFFIES msecs_to_jiffies(20)
     27 
     28 /*
     29  * Throttle our rendering by waiting until the ring has completed our requests
     30  * emitted over 20 msec ago.
     31  *
     32  * Note that if we were to use the current jiffies each time around the loop,
     33  * we wouldn't escape the function with any frames outstanding if the time to
     34  * render a frame was over 20ms.
     35  *
     36  * This should get us reasonable parallelism between CPU and GPU but also
     37  * relatively low latency when blocking on a particular request to finish.
     38  */
     39 int
     40 i915_gem_throttle_ioctl(struct drm_device *dev, void *data,
     41 			struct drm_file *file)
     42 {
     43 	struct drm_i915_file_private *file_priv = file->driver_priv;
     44 	unsigned long recent_enough = jiffies - DRM_I915_THROTTLE_JIFFIES;
     45 	struct i915_request *request, *target = NULL;
     46 	long ret;
     47 
     48 	/* ABI: return -EIO if already wedged */
     49 	ret = intel_gt_terminally_wedged(&to_i915(dev)->gt);
     50 	if (ret)
     51 		return ret;
     52 
     53 	spin_lock(&file_priv->mm.lock);
     54 	list_for_each_entry(request, &file_priv->mm.request_list, client_link) {
     55 		if (time_after_eq(request->emitted_jiffies, recent_enough))
     56 			break;
     57 
     58 		if (target && xchg(&target->file_priv, NULL))
     59 			list_del(&target->client_link);
     60 
     61 		target = request;
     62 	}
     63 	if (target)
     64 		i915_request_get(target);
     65 	spin_unlock(&file_priv->mm.lock);
     66 
     67 	if (!target)
     68 		return 0;
     69 
     70 	ret = i915_request_wait(target,
     71 				I915_WAIT_INTERRUPTIBLE,
     72 				MAX_SCHEDULE_TIMEOUT);
     73 	i915_request_put(target);
     74 
     75 	return ret < 0 ? ret : 0;
     76 }
     77