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