On Tue, 09 Apr 2019 18:13:04 +0200, Mika Kuoppala
<mika.kuoppala@xxxxxxxxxxxxxxx> wrote:
[snip]
+
+ /*
+ * 2c: Program Coarse Power Gating Policies.
+ *
+ * Bspec's guidance is to use 25us (really 25 * 1280ns) here. What we
+ * use instead is a more conservative estimate for the maximum time
+ * it takes us to service a CS interrupt and submit a new ELSP - that
+ * is the time which the GPU is idle waiting for the CPU to select the
+ * next request to execute. If the idle hysteresis is less than that
+ * interrupt service latency, the hardware will automatically gate
+ * the power well and we will then incur the wake up cost on top of
+ * the service latency. A similar guide from intel_pstate is that we
+ * do not want the enable hysteresis to less than the wakeup latency.
+ *
+ * igt/gem_exec_nop/sequential provides a rough estimate for the
+ * service latency, and puts it around 10us for Broadwell (and other
+ * big core) and around 40us for Broxton (and other low power cores).
+ * [Note that for legacy ringbuffer submission, this is less than 1us!]
+ * However, the wakeup latency on Broxton is closer to 100us. To be
+ * conservative, we have to factor in a context switch on top (due
+ * to ksoftirqd).
+ */
Do we want to copy legacy comments to Gen11 specific function ?
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