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/*
* SPDX-License-Identifier: MIT
*
* Copyright © 2014-2016 Intel Corporation
*/
#include <linux/jiffies.h>
#include <drm/drm_file.h>
#include "i915_drv.h"
#include "i915_gem_ioctls.h"
#include "i915_gem_object.h"
/*
* 20ms is a fairly arbitrary limit (greater than the average frame time)
* chosen to prevent the CPU getting more than a frame ahead of the GPU
* (when using lax throttling for the frontbuffer). We also use it to
* offer free GPU waitboosts for severely congested workloads.
*/
#define DRM_I915_THROTTLE_JIFFIES msecs_to_jiffies(20)
/*
* Throttle our rendering by waiting until the ring has completed our requests
* emitted over 20 msec ago.
*
* Note that if we were to use the current jiffies each time around the loop,
* we wouldn't escape the function with any frames outstanding if the time to
* render a frame was over 20ms.
*
* This should get us reasonable parallelism between CPU and GPU but also
* relatively low latency when blocking on a particular request to finish.
*/
int
i915_gem_throttle_ioctl(struct drm_device *dev, void *data,
struct drm_file *file)
{
struct drm_i915_file_private *file_priv = file->driver_priv;
unsigned long recent_enough = jiffies - DRM_I915_THROTTLE_JIFFIES;
struct i915_request *request, *target = NULL;
long ret;
/* ABI: return -EIO if already wedged */
ret = i915_terminally_wedged(to_i915(dev));
if (ret)
return ret;
spin_lock(&file_priv->mm.lock);
list_for_each_entry(request, &file_priv->mm.request_list, client_link) {
if (time_after_eq(request->emitted_jiffies, recent_enough))
break;
if (target) {
list_del(&target->client_link);
target->file_priv = NULL;
}
target = request;
}
if (target)
i915_request_get(target);
spin_unlock(&file_priv->mm.lock);
if (!target)
return 0;
ret = i915_request_wait(target,
I915_WAIT_INTERRUPTIBLE,
MAX_SCHEDULE_TIMEOUT);
i915_request_put(target);
return ret < 0 ? ret : 0;
}
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