1// SPDX-License-Identifier: MIT
2/*
3 * Copyright © 2014-2016 Intel Corporation
4 */
5
6#include <linux/jiffies.h>
7
8#include <drm/drm_file.h>
9
10#include "i915_drv.h"
11#include "i915_file_private.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 drm_i915_private *i915 = to_i915(dev);
42 struct i915_gem_context *ctx;
43 unsigned long idx;
44 long ret;
45
46 /* ABI: return -EIO if already wedged */
47 ret = intel_gt_terminally_wedged(gt: to_gt(i915));
48 if (ret)
49 return ret;
50
51 rcu_read_lock();
52 xa_for_each(&file_priv->context_xa, idx, ctx) {
53 struct i915_gem_engines_iter it;
54 struct intel_context *ce;
55
56 if (!kref_get_unless_zero(kref: &ctx->ref))
57 continue;
58 rcu_read_unlock();
59
60 for_each_gem_engine(ce,
61 i915_gem_context_lock_engines(ctx),
62 it) {
63 struct i915_request *rq, *target = NULL;
64
65 if (!ce->timeline)
66 continue;
67
68 mutex_lock(lock: &ce->timeline->mutex);
69 list_for_each_entry_reverse(rq,
70 &ce->timeline->requests,
71 link) {
72 if (i915_request_completed(rq))
73 break;
74
75 if (time_after(rq->emitted_jiffies,
76 recent_enough))
77 continue;
78
79 target = i915_request_get(rq);
80 break;
81 }
82 mutex_unlock(lock: &ce->timeline->mutex);
83 if (!target)
84 continue;
85
86 ret = i915_request_wait(rq: target,
87 I915_WAIT_INTERRUPTIBLE,
88 MAX_SCHEDULE_TIMEOUT);
89 i915_request_put(rq: target);
90 if (ret < 0)
91 break;
92 }
93 i915_gem_context_unlock_engines(ctx);
94 i915_gem_context_put(ctx);
95
96 rcu_read_lock();
97 }
98 rcu_read_unlock();
99
100 return ret < 0 ? ret : 0;
101}
102