formula given below. However, each thread also has an integer
@dfn{nice} value that determines how ``nice'' the thread should be to
other threads. A @var{nice} of zero does not affect thread priority. A
-positive @var{nice}, to the maximum of 20, increases the numeric
-priority of a thread, decreasing its effective priority, and causes it
-to give up some CPU time it would otherwise receive. On the other hand,
-a negative @var{nice}, to the minimum of -20, tends to take away CPU
-time from other threads.
+positive @var{nice}, to the maximum of 20, decreases the priority of a
+thread and causes it to give up some CPU time it would otherwise receive.
+On the other hand, a negative @var{nice}, to the minimum of -20, tends
+to take away CPU time from other threads.
The initial thread starts with a @var{nice} value of zero. Other
threads start with a @var{nice} value inherited from their parent
thread. You must implement the functions described below, which are for
use by test programs. We have provided skeleton definitions for them in
-@file{threads/thread.c}. by test programs
+@file{threads/thread.c}.
@deftypefun int thread_get_nice (void)
Returns the current thread's @var{nice} value.
@noindent where @var{recent_cpu} is an estimate of the CPU time the
thread has used recently (see below) and @var{nice} is the thread's
-@var{nice} value. The coefficients @math{1/4} and 2 on @var{recent_cpu}
+@var{nice} value. The result should be rounded down to the nearest
+integer (truncated).
+The coefficients @math{1/4} and 2 on @var{recent_cpu}
and @var{nice}, respectively, have been found to work well in practice
but lack deeper meaning. The calculated @var{priority} is always
adjusted to lie in the valid range @code{PRI_MIN} to @code{PRI_MAX}.
threads ready to run (see below). If @var{load_avg} is 1, indicating
that a single thread, on average, is competing for the CPU, then the
current value of @var{recent_cpu} decays to a weight of .1 in
-@am{\log_{2/3}.1 \approx 6, ln(2/3)/ln(.1) = approx. 6} seconds; if
+@am{\log_{2/3}.1 \approx 6, ln(.1)/ln(2/3) = approx. 6} seconds; if
@var{load_avg} is 2, then decay to a weight of .1 takes @am{\log_{3/4}.1
-\approx 8, ln(3/4)/ln(.1) = approx. 8} seconds. The effect is that
+\approx 8, ln(.1)/ln(3/4) = approx. 8} seconds. The effect is that
@var{recent_cpu} estimates the amount of CPU time the thread has
received ``recently,'' with the rate of decay inversely proportional to
the number of threads competing for the CPU.
-Assumptions made by some of the tests require that updates to
+Assumptions made by some of the tests require that these recalculations of
@var{recent_cpu} be made exactly when the system tick counter reaches a
multiple of a second, that is, when @code{timer_ticks () % TIMER_FREQ ==
0}, and not at any other time.
@node 4.4BSD Scheduler Summary
@section Summary
-This section summarizes the calculations required to implement the
-scheduler. It is not a complete description of scheduler requirements.
+The following formulas summarize the calculations required to implement the
+scheduler. They are not a complete description of scheduler requirements.
Every thread has a @var{nice} value between -20 and 20 directly under
its control. Each thread also has a priority, between 0
2^q, f = 2**q}. By the definition above, we can convert an integer or
real number into @m{p.q} format by multiplying with @m{f}. For example,
in 17.14 format the fraction 59/60 used in the calculation of
-@var{load_avg}, above, is @am{(59/60)2^{14}, 59/60*(2**14)} = 16,111
-(rounded to nearest). To convert a fixed-point value back to an
+@var{load_avg}, above, is @am{(59/60)2^{14}, 59/60*(2**14)} = 16,110.
+To convert a fixed-point value back to an
integer, divide by @m{f}. (The normal @samp{/} operator in C rounds
toward zero, that is, it rounds positive numbers down and negative
numbers up. To round to nearest, add @m{f / 2} to a positive number, or
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