drm/i915/slpc: Optmize waitboost for SLPC

Waitboost (when SLPC is enabled) results in a H2G message. This can result
in thousands of messages during a stress test and fill up an already full
CTB. There is no need to request for boost if min softlimit is equal or
greater than it.

v2: Add the tracing back, and check requested freq
in the worker thread (Tvrtko)
v3: Check requested freq in dec_waiters as well
v4: Only check min_softlimit against boost_freq. Limit this
optimization for server parts for now.
v5: min_softlimit can be greater than boost (Ashutosh)
Reviewed-by: Ashutosh Dixit <ashutosh.dixit@intel.com>
Signed-off-by: Vinay Belgaumkar <vinay.belgaumkar@intel.com>
Signed-off-by: John Harrison <John.C.Harrison@Intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20221024171108.14373-1-vinay.belgaumkar@intel.com

drivers/gpu/drm/i915/gt/intel_rps.c

@@ -1014,9 +1014,15 @@ void intel_rps_boost(struct i915_request *rq)
 		if (rps_uses_slpc(rps)) {
 			slpc = rps_to_slpc(rps);
 
+			if (slpc->min_freq_softlimit >= slpc->boost_freq)
+				return;
+
 			/* Return if old value is non zero */
-			if (!atomic_fetch_inc(&slpc->num_waiters))
+			if (!atomic_fetch_inc(&slpc->num_waiters)) {
+				GT_TRACE(rps_to_gt(rps), "boost fence:%llx:%llx\n",
+					 rq->fence.context, rq->fence.seqno);
 				schedule_work(&slpc->boost_work);
+			}
 
 			return;
 		}