clean up with comments

SCCS-vsn: sys/kern/kern_clock.c 4.40

diff --git a/usr/src/sys/kern/kern_clock.c b/usr/src/sys/kern/kern_clock.c
index bc24019..af7f00a 100644 (file)
--- a/usr/src/sys/kern/kern_clock.c
+++ b/usr/src/sys/kern/kern_clock.c
@@ -1,4 +1,4 @@
-/*     kern_clock.c    4.39    82/09/08        */
+/*     kern_clock.c    4.40    82/09/08        */

 
 #include "../h/param.h"
 #include "../h/systm.h"
 
 #include "../h/param.h"
 #include "../h/systm.h"


@@ -16,24 +16,41 @@
 #include "../h/share.h"
 #endif
 
 #include "../h/share.h"
 #endif
 

-#include "dh.h"
-#include "dz.h"
-#include "ps.h"
+/*
+ * Clock handling routines.
+ *
+ * This code is written for a machine with only one interval timer,
+ * and does timing and resource utilization estimation statistically
+ * based on the state of the machine hz times a second.  A machine
+ * with proper clocks (running separately in user state, system state,
+ * interrupt state and idle state) as well as a time-of-day clock
+ * would allow a non-approximate implementation.
+ */

 
 

-#ifdef GPROF
-extern int profiling;
-extern char *s_lowpc;
-extern u_long s_textsize;
-extern u_short *kcount;
-#endif
+/*
+ * TODO:
+ *     * Keep more accurate statistics by simulating good interval timers.
+ *     * Use the time-of-day clock on the VAX to keep more accurate time
+ *       than is possible by repeated use of the interval timer.
+ *     * Allocate more timeout table slots when table overflows.
+ */

 
 

-#define        bumptime(tp)    \
-       (tp)->tv_usec += tick; \
+/* bump a timeval by a small number of usec's */
+#define        bumptime(tp, usec) \
+       (tp)->tv_usec += usec; \

        if ((tp)->tv_usec >= 1000000) { \
                (tp)->tv_usec -= 1000000; \
                (tp)->tv_sec++; \
        }
 
        if ((tp)->tv_usec >= 1000000) { \
                (tp)->tv_usec -= 1000000; \
                (tp)->tv_sec++; \
        }
 

+/*
+ * The (single) hardware interval timer.
+ * We update the events relating to real time, and then
+ * make a gross assumption: that the system has been in the
+ * state it is in (user state, kernel state, interrupt state,
+ * or idle state) for the entire last time interval, and
+ * update statistics accordingly.
+ */

 /*ARGSUSED*/
 hardclock(pc, ps)
        caddr_t pc;
 /*ARGSUSED*/
 hardclock(pc, ps)
        caddr_t pc;


@@ -43,17 +60,29 @@ hardclock(pc, ps)
        register int s, cpstate;
        extern double avenrun[];
 
        register int s, cpstate;
        extern double avenrun[];
 

-#if NPS > 0
-       psextsync(pc, ps);
-#endif
-
-/* update callout times */
+       /*
+        * Update real-time timeout queue.
+        * At front of queue are some number of events which are ``due''.
+        * The time to these is <= 0 and if negative represents the
+        * number of ticks which have passed since it was supposed to happen.
+        * The rest of the q elements (times > 0) are events yet to happen,
+        * where the time for each is given as a delta from the previous.
+        * Decrementing just the first of these serves to decrement the time
+        * to all events.
+        */

        for (p1 = calltodo.c_next; p1 && p1->c_time <= 0; p1 = p1->c_next)
                --p1->c_time;
        if (p1)
                --p1->c_time;
 
        for (p1 = calltodo.c_next; p1 && p1->c_time <= 0; p1 = p1->c_next)
                --p1->c_time;
        if (p1)
                --p1->c_time;
 

-/* charge process for resource usage... statistically! */
+       /*
+        * If the cpu is currently scheduled to a process, then
+        * charge it with resource utilization for a tick, updating
+        * statistics which run in (user+system) virtual time,
+        * such as the cpu time limit and profiling timers.
+        * This assumes that the current process has been running
+        * the entire last tick.
+        */

        if (!noproc) {
                s = u.u_procp->p_rssize;
                u.u_ru.ru_idrss += s; u.u_ru.ru_isrss += 0;     /* XXX */
        if (!noproc) {
                s = u.u_procp->p_rssize;
                u.u_ru.ru_idrss += s; u.u_ru.ru_isrss += 0;     /* XXX */


@@ -77,9 +106,19 @@ hardclock(pc, ps)
                        psignal(u.u_procp, SIGPROF);
        }
 
                        psignal(u.u_procp, SIGPROF);
        }
 

-/* charge for cpu */
+       /*
+        * Charge the time out based on the mode the cpu is in.
+        * Here again we fudge for the lack of proper interval timers
+        * assuming that the current state has been around at least
+        * one tick.
+        */

        if (USERMODE(ps)) {
        if (USERMODE(ps)) {

-               bumptime(&u.u_ru.ru_utime);
+               /*
+                * CPU was in user state.  Increment
+                * user time counter, and process process-virtual time
+                * interval timer.
+                */
+               bumptime(&u.u_ru.ru_utime, tick);

                if (timerisset(&u.u_timer[ITIMER_VIRTUAL].it_value) &&
                    itimerdecr(&u.u_timer[ITIMER_VIRTUAL], tick) == 0)
                        psignal(u.u_procp, SIGVTALRM);
                if (timerisset(&u.u_timer[ITIMER_VIRTUAL].it_value) &&
                    itimerdecr(&u.u_timer[ITIMER_VIRTUAL], tick) == 0)
                        psignal(u.u_procp, SIGVTALRM);


@@ -88,6 +127,17 @@ hardclock(pc, ps)
                else
                        cpstate = CP_USER;
        } else {
                else
                        cpstate = CP_USER;
        } else {

+               /*
+                * CPU was in system state.  If profiling kernel
+                * increment a counter.  If no process is running
+                * then this is a system tick if we were running
+                * at a non-zero IPL (in a driver).  If a process is running,
+                * then we charge it with system time even if we were
+                * at a non-zero IPL, since the system often runs
+                * this way during processing of system calls.
+                * This is approximate, but the lack of true interval
+                * timers makes doing anything else difficult.
+                */

 #ifdef GPROF
                int k = pc - s_lowpc;
                if (profiling < 2 && k < s_textsize)
 #ifdef GPROF
                int k = pc - s_lowpc;
                if (profiling < 2 && k < s_textsize)


@@ -98,17 +148,34 @@ hardclock(pc, ps)
                        if ((ps&PSL_IPL) != 0)
                                cpstate = CP_IDLE;
                } else {
                        if ((ps&PSL_IPL) != 0)
                                cpstate = CP_IDLE;
                } else {

-                       bumptime(&u.u_ru.ru_stime);
+                       bumptime(&u.u_ru.ru_stime, tick);

                }
        }
 
                }
        }
 

-/* iostat statistics */
+       /*
+        * We maintain statistics shown by user-level statistics
+        * programs:  the amount of time in each cpu state, and
+        * the amount of time each of DK_NDRIVE ``drives'' is busy.
+        */

        cp_time[cpstate]++;
        for (s = 0; s < DK_NDRIVE; s++)
                if (dk_busy&(1<<s))
                        dk_time[s]++;
 
        cp_time[cpstate]++;
        for (s = 0; s < DK_NDRIVE; s++)
                if (dk_busy&(1<<s))
                        dk_time[s]++;
 

-/* adjust priority of current process */
+       /*
+        * We adjust the priority of the current process.
+        * The priority of a process gets worse as it accumulates
+        * CPU time.  The cpu usage estimator (p_cpu) is increased here
+        * and the formula for computing priorities (in kern_synch.c)
+        * will compute a different value each time the p_cpu increases
+        * by 4.  The cpu usage estimator ramps up quite quickly when
+        * the process is running (linearly), and decays away exponentially,
+        * at a rate which is proportionally slower when the system is
+        * busy.  The basic principal is that the system will 90% forget
+        * that a process used a lot of CPU time in 5*loadav seconds.
+        * This causes the system to favor processes which haven't run
+        * much recently, and to round-robin among other processes.
+        */

        if (!noproc) {
                p = u.u_procp;
                p->p_cpticks++;
        if (!noproc) {
                p = u.u_procp;
                p->p_cpticks++;


@@ -119,56 +186,50 @@ hardclock(pc, ps)
                    (shconsts.sc_tic * ((2*NZERO)-p->p_nice)) / NZERO :
                    shconsts.sc_tic) * (((int)avenrun[0]+2)/3);
 #endif
                    (shconsts.sc_tic * ((2*NZERO)-p->p_nice)) / NZERO :
                    shconsts.sc_tic) * (((int)avenrun[0]+2)/3);
 #endif

-               if (p->p_cpu % 4 == 0) {
+               if ((p->p_cpu&3) == 0) {

                        (void) setpri(p);
                        if (p->p_pri >= PUSER)
                                p->p_pri = p->p_usrpri;
                }
        }
                        (void) setpri(p);
                        if (p->p_pri >= PUSER)
                                p->p_pri = p->p_usrpri;
                }
        }

-       bumptime(&time);
+
+       /*
+        * Increment the time-of-day, and schedule
+        * processing of the callouts at a very low cpu priority,
+        * so we don't keep the relatively high clock interrupt
+        * priority any longer than necessary.
+        */
+       bumptime(&time, tick);

        setsoftclock();
 }
 
        setsoftclock();
 }
 

+/*
+ * Software priority level clock interrupt.
+ * Run periodic events from timeout queue.
+ */

 /*ARGSUSED*/
 softclock(pc, ps)
        caddr_t pc;
 {
 /*ARGSUSED*/
 softclock(pc, ps)
        caddr_t pc;
 {

-       register struct callout *p1;
-       register int a, s;
-       caddr_t arg;
-       int (*func)();

 
 

-       if (panicstr)
-               goto nocallout;

        for (;;) {
        for (;;) {

+               register struct callout *p1;
+               register caddr_t arg;
+               register int (*func)();
+               register int a, s;
+

                s = spl7();
                if ((p1 = calltodo.c_next) == 0 || p1->c_time > 0) {
                        splx(s);
                        break;
                }
                s = spl7();
                if ((p1 = calltodo.c_next) == 0 || p1->c_time > 0) {
                        splx(s);
                        break;
                }

+               arg = p1->c_arg; func = p1->c_func; a = p1->c_time;

                calltodo.c_next = p1->c_next;
                calltodo.c_next = p1->c_next;

-               arg = p1->c_arg;
-               func = p1->c_func;
-               a = p1->c_time;

                p1->c_next = callfree;
                callfree = p1;
                (void) splx(s);
                (*func)(arg, a);
        }
                p1->c_next = callfree;
                callfree = p1;
                (void) splx(s);
                (*func)(arg, a);
        }

-nocallout:
-
-#if NDH > 0
-       s = spl5(); dhtimer(); splx(s);
-#endif
-#if NDZ > 0
-       s = spl5(); dztimer(); splx(s);
-#endif
-
-/* if nothing to do, try swapin */
-       if (noproc && runin) {
-               runin = 0;
-               wakeup((caddr_t)&runin);
-       }

 }
 
 /*
 }
 
 /*


@@ -226,14 +287,35 @@ untimeout(fun, arg)
        splx(s);
 }
 
        splx(s);
 }
 

+/*
+ * Compute number of hz until specified time.
+ * Used to compute third argument to timeout() from an
+ * absolute time.
+ */

 hzto(tv)
        struct timeval *tv;
 {
 hzto(tv)
        struct timeval *tv;
 {

-       register int ticks;
+       register long ticks;
+       register long sec;

        int s = spl7();
 
        int s = spl7();
 

-       ticks = ((tv->tv_sec - time.tv_sec) * 1000 +
-               (tv->tv_usec - time.tv_usec) / 1000) / (tick / 1000);
+       /*
+        * If number of milliseconds will fit in 32 bit arithmetic,
+        * then compute number of milliseconds to time and scale to
+        * ticks.  Otherwise just compute number of hz in time, rounding
+        * times greater than representible to maximum value.
+        *
+        * Delta times less than 25 days can be computed ``exactly''.
+        * Maximum value for any timeout in 10ms ticks is 250 days.
+        */
+       sec = tv->tv_sec - time.tv_sec;
+       if (sec <= 0x7fffffff / 1000 - 1000)
+               ticks = ((tv->tv_sec - time.tv_sec) * 1000 +
+                       (tv->tv_usec - time.tv_usec) / 1000) / (tick / 1000);
+       else if (sec <= 0x7fffffff / hz)
+               ticks = sec * hz;
+       else
+               ticks = 0x7fffffff;

        splx(s);
        return (ticks);
 }
        splx(s);
        return (ticks);
 }