PEP 418: another benchmark on FreeBSD
Add also more info on FreeBSD timecounters
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Victor Stinner
parent
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commit
a15d634866
68
pep-0418.txt
68
pep-0418.txt
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@ -333,6 +333,33 @@ Each function was called 10,000,000 times and CLOCK_MONOTONIC was used to get
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the time before and after. The benchmark was run 5 times to keep the minimum
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time.
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FreeBSD 8.0 in kvm with hardware virtualization:
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======================== ====== ========= ======= =======
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Function TSC ACPI-Safe HPET i8254
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======================== ====== ========= ======= =======
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time() 191 ns 188 ns 189 ns 188 ns
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CLOCK_SECOND 187 ns 184 ns 187 ns 183 ns
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CLOCK_REALTIME_FAST 189 ns 180 ns 187 ns 190 ns
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CLOCK_UPTIME_FAST 191 ns 185 ns 186 ns 196 ns
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CLOCK_MONOTONIC_FAST 188 ns 187 ns 188 ns 189 ns
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CLOCK_THREAD_CPUTIME_ID 208 ns 206 ns 207 ns 220 ns
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CLOCK_VIRTUAL 280 ns 279 ns 283 ns 296 ns
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CLOCK_PROF 289 ns 280 ns 282 ns 286 ns
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clock() 342 ns 340 ns 337 ns 344 ns
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CLOCK_UPTIME_PRECISE 197 ns 10380 ns 4402 ns 4097 ns
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CLOCK_REALTIME 196 ns 10376 ns 4337 ns 4054 ns
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CLOCK_MONOTONIC_PRECISE 198 ns 10493 ns 4413 ns 3958 ns
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CLOCK_UPTIME 197 ns 10523 ns 4458 ns 4058 ns
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gettimeofday() 202 ns 10524 ns 4186 ns 3962 ns
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CLOCK_REALTIME_PRECISE 197 ns 10599 ns 4394 ns 4060 ns
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CLOCK_MONOTONIC 201 ns 10766 ns 4498 ns 3943 ns
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======================== ====== ========= ======= =======
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Each function was called 100,000 times and CLOCK_MONOTONIC was used to get
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the time before and after. The benchmark was run 5 times to keep the minimum
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time.
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NTP adjustment
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@ -827,16 +854,17 @@ source to decide which one will be used.
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so usually higher than 1 GHz. Its priority is 300 by default, but
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falls to 0 if the processor frequency changes and the counter
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becomes unstable.
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* HPET: An HPET chip consists of a 64-bit up-counter (main counter)
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counting at least at 10 MHz and a set of up to 256 comparators (at
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least 3). Each HPET can have up to 32 timers.
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* HPET: An High Precision Event Timer (HPET) chip consists of a 64-bit
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up-counter (main counter) counting at least at 10 MHz and a set of up to 256
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comparators (at least 3). Each HPET can have up to 32 timers. HPET can
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cause around 3 seconds of drift per day.
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* PIT (programmable interrupt timer): Intel 8253/8254 chipsets with a
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configurable frequency in range 18.2 Hz - 1.2 MHz. Linux uses the
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frequency 1,193,181.8 Hz. It is a 16-bit counter.
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* PMTMR (power management timer): ACPI 24-bit timer with a frequency
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of 3.5 MHz (3,579,545 Hz). Its priority is 200 by default, but
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changes to 110 if the chipset is broken and need a software
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workaround. HPET can cause around 3 seconds of drift per day.
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workaround.
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* Cyclone: The Cyclone timer uses a 32-bit counter on IBM Extended
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X-Architecture (EXA) chipsets which include computers that use the
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IBM "Summit" series chipsets (ex: x440). This is available in IA32
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@ -859,11 +887,38 @@ Read also the `time(7) manual page
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FreeBSD timers
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--------------
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The sysctl program can be used to change the timecounter. For example::
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kern.timecounter.choice list available hardward clocks with their priority.
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The sysctl program can be used to change the timecounter. Example::
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# dmesg|grep Timecounter
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Timecounter "i8254" frequency 1193182 Hz quality 0
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Timecounter "ACPI-safe" frequency 3579545 Hz quality 850
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Timecounter "HPET" frequency 100000000 Hz quality 900
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Timecounter "TSC" frequency 3411154800 Hz quality 800
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Timecounters tick every 10.000 msec
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# sysctl kern.timecounter.choice
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kern.timecounter.choice: TSC(800) HPET(900) ACPI-safe(850) i8254(0) dummy(-1000000)
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# sysctl kern.timecounter.hardware="ACPI-fast"
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kern.timecounter.hardware: HPET -> ACPI-fast
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Available clocks:
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* "TSC": Time Stamp Counter of the procesor
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* "HPET": High Precision Event Timer
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* "ACPI-fast": ACPI Power Management timer (fast mode)
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* "ACPI-safe": ACPI Power Management timer (safe mode)
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* "i8254": PIT with Intel 8254 chipset
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The `commit 222222
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<http://svnweb.freebsd.org/base?view=revision&revision=222222>`_ (May 2011)
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decreased ACPI-fast timecounter quality to 900 and increased HPET timecounter
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quality to 950: "HPET on modern platforms usually have better resolution and
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lower latency than ACPI timer".
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Read `Timecounters: Efficient and precise timekeeping in SMP kernels
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<http://phk.freebsd.dk/pubs/timecounter.pdf`_ by Poul-Henning Kamp (2002) for
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the FreeBSD Project.
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Sleep, suspend and monotonic time
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=================================
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@ -1247,6 +1302,9 @@ Time:
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bits of time
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* `Win32 Performance Measurement Options
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<http://drdobbs.com/windows/184416651>`_ by Matthew Wilson, May 01, 2003
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* `Counter Availability and Characteristics for Feed-forward Based Synchronization
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<http://www.cubinlab.ee.unimelb.edu.au/~jrid/Publications/ridoux_ispcs09.pdf>`_
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by Timothy Broomhead, Julien Ridoux, Darryl Veitch (2009)
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* System Management Interrupt (SMI) issues:
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* `System Management Interrupt Free Hardware
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