Mention heartbeats

Author: polytypic

lib/picos_mux.multififo/picos_mux_multififo.mli

@@ -3,14 +3,17 @@
 
     This scheduler uses a queue per thread to implement a mostly FIFO scheduler.
     If a thread runs out of fibers to run, it will try to take a fiber from the
-    queues of other threads. Furthermore, threads periodically consider taking
-    fibers from other threads to balance the number of fibers per thread. All of
-    this means that this scheduler should act relatively fairly and work well
-    for concurrent workloads and workloads where fairness matters. This
-    scheduler also gives priority to fibers woken up due to being canceled.
-
-    🐌 Due to mostly FIFO scheduling this scheduler performs poorly on highly
-    parallel workloads.
+    queues of other threads. Threads also periodically consider taking fibers
+    from other threads to balance the number of fibers per thread. If threads
+    cannot find work, they will go to sleep. A separate heartbeat thread is used
+    to wake up threads periodically. All of this means that this scheduler
+    should act relatively fairly and work well for concurrent workloads and
+    workloads where fairness matters and that short bursts of parallelism should
+    not cause slowdowns. This scheduler also gives priority to fibers woken up
+    due to being canceled.
+
+    🐌 Due to mostly FIFO scheduling this scheduler performs poorly on CPU bound
+    fine grained parallel workloads.
 
     ℹ️ See {!Picos_mux_fifo} for a single-threaded variation of this scheduler.