module Calibrator:sig
..end
.ml
file)
Calibration at the rate of 0.1, 1 or 2 secs produces errors (measured as the
difference between Time.now
and the reported time here) on the order of 1-2us.
Given the precision of 52bit float mantissa values, this is very close to least error
one can have on these values. Calibration once per 10sec produces errors that are
+/-4us. Calibration once per minute produces errors that are +/-15us and calibration
once in 3mins produces errors +/-30us. (It is worth remarking that the error has a
positive bias of 1us -- i.e. the error dances around the 1us mark, rather than around
0. It is unclear where this bias is introduced, though it probably does not matter for
most applications.)
This module maintains an instance of t
internal to the module. The internal
instance of t
can be updated via calls to calibrate ()
, i.e. without specifying
the t
parameter. In all the functions below that take an optional Calibrator.t
argument, the internal instance is used when no calibrator is explicitly specified.
type
t
val create : unit -> t
create ()
creates an uninitialized calibrator instance. Creating a calibrator
takes about 3ms. One needs a recently calibrated Calibrator.t
and the TSC value
from the same machine to meaningfully convert the TSC value to a Time.t
.val calibrate : ?t:t -> unit -> unit
calibrate ~t
updates t
by measuring the current value of the TSC and
Time.now
.val cpu_mhz : (?t:t -> unit -> float) Or_error.t
Time.now ()
. This function is undefined on 32bit machines.val t_of_sexp : Sexplib.Sexp.t -> t
val sexp_of_t : t -> Sexplib.Sexp.t
val bin_t : t Bin_prot.Type_class.t
val bin_read_t : t Bin_prot.Read.reader
val __bin_read_t__ : (int -> t) Bin_prot.Read.reader
val bin_reader_t : t Bin_prot.Type_class.reader
val bin_size_t : t Bin_prot.Size.sizer
val bin_write_t : t Bin_prot.Write.writer
val bin_writer_t : t Bin_prot.Type_class.writer
create ()
creates an uninitialized calibrator instance. Creating a calibrator
takes about 3ms. One needs a recently calibrated Calibrator.t
and the TSC value
from the same machine to meaningfully convert the TSC value to a Time.t
.calibrate ~t
updates t
by measuring the current value of the TSC and
Time.now
.Time.now ()
. This function is undefined on 32bit machines.