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-rw-r--r--drivers/gpu/drm/i915/i915_gem.c47
1 files changed, 45 insertions, 2 deletions
diff --git a/drivers/gpu/drm/i915/i915_gem.c b/drivers/gpu/drm/i915/i915_gem.c
index 06631e130efc..8719fa2ae7e7 100644
--- a/drivers/gpu/drm/i915/i915_gem.c
+++ b/drivers/gpu/drm/i915/i915_gem.c
@@ -1146,14 +1146,57 @@ static bool missed_irq(struct drm_i915_private *dev_priv,
return test_bit(ring->id, &dev_priv->gpu_error.missed_irq_rings);
}
+static unsigned long local_clock_us(unsigned *cpu)
+{
+ unsigned long t;
+
+ /* Cheaply and approximately convert from nanoseconds to microseconds.
+ * The result and subsequent calculations are also defined in the same
+ * approximate microseconds units. The principal source of timing
+ * error here is from the simple truncation.
+ *
+ * Note that local_clock() is only defined wrt to the current CPU;
+ * the comparisons are no longer valid if we switch CPUs. Instead of
+ * blocking preemption for the entire busywait, we can detect the CPU
+ * switch and use that as indicator of system load and a reason to
+ * stop busywaiting, see busywait_stop().
+ */
+ *cpu = get_cpu();
+ t = local_clock() >> 10;
+ put_cpu();
+
+ return t;
+}
+
+static bool busywait_stop(unsigned long timeout, unsigned cpu)
+{
+ unsigned this_cpu;
+
+ if (time_after(local_clock_us(&this_cpu), timeout))
+ return true;
+
+ return this_cpu != cpu;
+}
+
static int __i915_spin_request(struct drm_i915_gem_request *req, int state)
{
unsigned long timeout;
+ unsigned cpu;
+
+ /* When waiting for high frequency requests, e.g. during synchronous
+ * rendering split between the CPU and GPU, the finite amount of time
+ * required to set up the irq and wait upon it limits the response
+ * rate. By busywaiting on the request completion for a short while we
+ * can service the high frequency waits as quick as possible. However,
+ * if it is a slow request, we want to sleep as quickly as possible.
+ * The tradeoff between waiting and sleeping is roughly the time it
+ * takes to sleep on a request, on the order of a microsecond.
+ */
if (i915_gem_request_get_ring(req)->irq_refcount)
return -EBUSY;
- timeout = jiffies + 1;
+ timeout = local_clock_us(&cpu) + 5;
while (!need_resched()) {
if (i915_gem_request_completed(req, true))
return 0;
@@ -1161,7 +1204,7 @@ static int __i915_spin_request(struct drm_i915_gem_request *req, int state)
if (signal_pending_state(state, current))
break;
- if (time_after_eq(jiffies, timeout))
+ if (busywait_stop(timeout, cpu))
break;
cpu_relax_lowlatency();