PEP 418: another benchmark on FreeBSD

Add also more info on FreeBSD timecounters

pep-0418.txt

@@ -333,6 +333,33 @@ Each function was called 10,000,000 times and CLOCK_MONOTONIC was used to get
 the time before and after. The benchmark was run 5 times to keep the minimum
 time.
 
+FreeBSD 8.0 in kvm with hardware virtualization:
+
+========================  ======  =========  =======  =======
+Function                  TSC     ACPI-Safe  HPET     i8254
+========================  ======  =========  =======  =======
+time()                    191 ns    188 ns    189 ns   188 ns
+CLOCK_SECOND              187 ns    184 ns    187 ns   183 ns
+CLOCK_REALTIME_FAST       189 ns    180 ns    187 ns   190 ns
+CLOCK_UPTIME_FAST         191 ns    185 ns    186 ns   196 ns
+CLOCK_MONOTONIC_FAST      188 ns    187 ns    188 ns   189 ns
+CLOCK_THREAD_CPUTIME_ID   208 ns    206 ns    207 ns   220 ns
+CLOCK_VIRTUAL             280 ns    279 ns    283 ns   296 ns
+CLOCK_PROF                289 ns    280 ns    282 ns   286 ns
+clock()                   342 ns    340 ns    337 ns   344 ns
+CLOCK_UPTIME_PRECISE      197 ns  10380 ns   4402 ns  4097 ns
+CLOCK_REALTIME            196 ns  10376 ns   4337 ns  4054 ns
+CLOCK_MONOTONIC_PRECISE   198 ns  10493 ns   4413 ns  3958 ns
+CLOCK_UPTIME              197 ns  10523 ns   4458 ns  4058 ns
+gettimeofday()            202 ns  10524 ns   4186 ns  3962 ns
+CLOCK_REALTIME_PRECISE    197 ns  10599 ns   4394 ns  4060 ns
+CLOCK_MONOTONIC           201 ns  10766 ns   4498 ns  3943 ns
+========================  ======  =========  =======  =======
+
+Each function was called 100,000 times and CLOCK_MONOTONIC was used to get
+the time before and after. The benchmark was run 5 times to keep the minimum
+time.
+
 
 
 NTP adjustment
@@ -827,16 +854,17 @@ source to decide which one will be used.
   so usually higher than 1 GHz.  Its priority is 300 by default, but
   falls to 0 if the processor frequency changes and the counter
   becomes unstable.
-* HPET: An HPET chip consists of a 64-bit up-counter (main counter)
+* HPET: An High Precision Event Timer (HPET) chip consists of a 64-bit
-  counting at least at 10 MHz and a set of up to 256 comparators (at
+  up-counter (main counter) counting at least at 10 MHz and a set of up to 256
-  least 3).  Each HPET can have up to 32 timers.
+  comparators (at least 3).  Each HPET can have up to 32 timers.  HPET can
+  cause around 3 seconds of drift per day.
 * PIT (programmable interrupt timer): Intel 8253/8254 chipsets with a
   configurable frequency in range 18.2 Hz - 1.2 MHz.  Linux uses the
   frequency 1,193,181.8 Hz.  It is a 16-bit counter.
 * PMTMR (power management timer): ACPI 24-bit timer with a frequency
   of 3.5 MHz (3,579,545 Hz).  Its priority is 200 by default, but
   changes to 110 if the chipset is broken and need a software
-  workaround.  HPET can cause around 3 seconds of drift per day.
+  workaround.
 * Cyclone: The Cyclone timer uses a 32-bit counter on IBM Extended
   X-Architecture (EXA) chipsets which include computers that use the
   IBM "Summit" series chipsets (ex: x440).  This is available in IA32
@@ -859,11 +887,38 @@ Read also the `time(7) manual page
 FreeBSD timers
 --------------
 
-The sysctl program can be used to change the timecounter. For example::
+kern.timecounter.choice list available hardward clocks with their priority.
+The sysctl program can be used to change the timecounter. Example::
 
+    # dmesg|grep Timecounter
+    Timecounter "i8254" frequency 1193182 Hz quality 0
+    Timecounter "ACPI-safe" frequency 3579545 Hz quality 850
+    Timecounter "HPET" frequency 100000000 Hz quality 900
+    Timecounter "TSC" frequency 3411154800 Hz quality 800
+    Timecounters tick every 10.000 msec
+    # sysctl kern.timecounter.choice
+    kern.timecounter.choice: TSC(800) HPET(900) ACPI-safe(850) i8254(0) dummy(-1000000)
     # sysctl kern.timecounter.hardware="ACPI-fast"
     kern.timecounter.hardware: HPET -> ACPI-fast
 
+Available clocks:
+
+ * "TSC": Time Stamp Counter of the procesor
+ * "HPET": High Precision Event Timer
+ * "ACPI-fast": ACPI Power Management timer (fast mode)
+ * "ACPI-safe": ACPI Power Management timer (safe mode)
+ * "i8254": PIT with Intel 8254 chipset
+
+The `commit 222222
+<http://svnweb.freebsd.org/base?view=revision&revision=222222>`_ (May 2011)
+decreased ACPI-fast timecounter quality to 900 and increased HPET timecounter
+quality to 950: "HPET on modern platforms usually have better resolution and
+lower latency than ACPI timer".
+
+Read `Timecounters: Efficient and precise timekeeping in SMP kernels
+<http://phk.freebsd.dk/pubs/timecounter.pdf`_ by Poul-Henning Kamp (2002) for
+the FreeBSD Project.
+
 
 Sleep, suspend and monotonic time
 =================================
@@ -1247,6 +1302,9 @@ Time:
   bits of time
 * `Win32 Performance Measurement Options
   <http://drdobbs.com/windows/184416651>`_ by Matthew Wilson, May 01, 2003
+* `Counter Availability and Characteristics for Feed-forward Based Synchronization
+  <http://www.cubinlab.ee.unimelb.edu.au/~jrid/Publications/ridoux_ispcs09.pdf>`_
+  by Timothy Broomhead, Julien Ridoux, Darryl Veitch (2009)
 * System Management Interrupt (SMI) issues:
 
   * `System Management Interrupt Free Hardware