Add a documentation about the Bechamel_perf module

lib/perf/bechamel_perf.mli

@@ -0,0 +1,52 @@
+(** This module provides several event counters from the [perf] API provided by
+    Linux (2.6+) - and they are {b not} compatible with other systems. These
+    counters are basically what the [perf] command provides.
+
+    For some events, it is necessary {b to be root}. If you try to use these
+    counters with insufficient privileges, [Bechamel_perf] will report you an
+    permission error.
+
+    If you want to use [Bechamel_perf] as a normal user, you should take a look
+    on {{:https://www.kernel.org/doc/Documentation/sysctl/kernel.txt}the
+    documentation about [perf_paranoid]}.
+*)
+
+open Bechamel
+
+module Extension : sig
+  val cycles : Mperf.t Measure.measure
+  val instructions : Mperf.t Measure.measure
+  val cache_references : Mperf.t Measure.measure
+  val cache_misses : Mperf.t Measure.measure
+  val branch_instructions : Mperf.t Measure.measure
+  val branch_misses : Mperf.t Measure.measure
+  val cpu_clock : Mperf.t Measure.measure
+  val task_clock : Mperf.t Measure.measure
+  val page_faults : Mperf.t Measure.measure
+  val context_switches : Mperf.t Measure.measure
+  val cpu_migrations : Mperf.t Measure.measure
+  val page_faults_min : Mperf.t Measure.measure
+  val page_faults_maj : Mperf.t Measure.measure
+  val alignment_faults : Mperf.t Measure.measure
+  val emulation_faults : Mperf.t Measure.measure
+  val dummy : Mperf.t Measure.measure
+end
+
+module Instance : sig
+  val cycles : Measure.witness
+  val instructions : Measure.witness
+  val cache_references : Measure.witness
+  val cache_misses : Measure.witness
+  val branch_instructions : Measure.witness
+  val branch_misses : Measure.witness
+  val cpu_clock : Measure.witness
+  val task_clock : Measure.witness
+  val page_faults : Measure.witness
+  val context_switches : Measure.witness
+  val cpu_migrations : Measure.witness
+  val page_faults_min : Measure.witness
+  val page_faults_maj : Measure.witness
+  val alignment_faults : Measure.witness
+  val emulation_faults : Measure.witness
+  val dummy : Measure.witness
+end