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_file_private.h"
 13#include "i915_gem_context.h"
 14#include "i915_gem_ioctls.h"
 15#include "i915_gem_object.h"
 16
 17/*
 18 * 20ms is a fairly arbitrary limit (greater than the average frame time)
 19 * chosen to prevent the CPU getting more than a frame ahead of the GPU
 20 * (when using lax throttling for the frontbuffer). We also use it to
 21 * offer free GPU waitboosts for severely congested workloads.
 22 */
 23#define DRM_I915_THROTTLE_JIFFIES msecs_to_jiffies(20)
 24
 25/*
 26 * Throttle our rendering by waiting until the ring has completed our requests
 27 * emitted over 20 msec ago.
 28 *
 29 * Note that if we were to use the current jiffies each time around the loop,
 30 * we wouldn't escape the function with any frames outstanding if the time to
 31 * render a frame was over 20ms.
 32 *
 33 * This should get us reasonable parallelism between CPU and GPU but also
 34 * relatively low latency when blocking on a particular request to finish.
 35 */
 36int
 37i915_gem_throttle_ioctl(struct drm_device *dev, void *data,
 38			struct drm_file *file)
 39{
 40	const unsigned long recent_enough = jiffies - DRM_I915_THROTTLE_JIFFIES;
 41	struct drm_i915_file_private *file_priv = file->driver_priv;
 42	struct drm_i915_private *i915 = to_i915(dev);
 43	struct i915_gem_context *ctx;
 44	unsigned long idx;
 45	long ret;
 46
 47	/* ABI: return -EIO if already wedged */
 48	ret = intel_gt_terminally_wedged(to_gt(i915));
 49	if (ret)
 50		return ret;
 51
 52	rcu_read_lock();
 53	xa_for_each(&file_priv->context_xa, idx, ctx) {
 54		struct i915_gem_engines_iter it;
 55		struct intel_context *ce;
 56
 57		if (!kref_get_unless_zero(&ctx->ref))
 58			continue;
 59		rcu_read_unlock();
 60
 61		for_each_gem_engine(ce,
 62				    i915_gem_context_lock_engines(ctx),
 63				    it) {
 64			struct i915_request *rq, *target = NULL;
 65
 66			if (!ce->timeline)
 67				continue;
 68
 69			mutex_lock(&ce->timeline->mutex);
 70			list_for_each_entry_reverse(rq,
 71						    &ce->timeline->requests,
 72						    link) {
 73				if (i915_request_completed(rq))
 74					break;
 75
 76				if (time_after(rq->emitted_jiffies,
 77					       recent_enough))
 78					continue;
 79
 80				target = i915_request_get(rq);
 81				break;
 82			}
 83			mutex_unlock(&ce->timeline->mutex);
 84			if (!target)
 85				continue;
 86
 87			ret = i915_request_wait(target,
 88						I915_WAIT_INTERRUPTIBLE,
 89						MAX_SCHEDULE_TIMEOUT);
 90			i915_request_put(target);
 91			if (ret < 0)
 92				break;
 93		}
 94		i915_gem_context_unlock_engines(ctx);
 95		i915_gem_context_put(ctx);
 96
 97		rcu_read_lock();
 98	}
 99	rcu_read_unlock();
100
101	return ret < 0 ? ret : 0;
102}