Removed mostly-dead code for setting switchtime after the idle loop

clobbers this variable.  Long ago, when the idle loop wasn't in a
process, it set switchtime.tv_sec to zero to indicate that the time
needs to be read after the idle loop finishes.  The special case for
this isn't needed now that there is an idle process (for each CPU).
The time is read in the normal way when the idle process is switched
away from.  The seconds component of the time is only zero for the
first second after the uptime is set, and the mostly-dead code was only
executed during this time.  (This was slightly broken by using uptimes
instead of times relative to the Epoch -- in the original version the
seconds component of the time was only 0 for the first second after
the Epoch.)

In mi_switch(), moved the setting of switchticks to just after the
first (and now only) setting of switchtime.  This setting used to be
delayed since a late setting was needed for the idle case and an early
setting was not needed.  Now the early setting is needed so that
fork_exit() doesn't need to set either switchtime or switchticks.
Removed now-completely-rotted comment attached to this.  Most of the
code described by the comment had already moved to sched_switch().

2 files changed, 2 insertions, 11 deletions

diff --git a/sys/kern/kern_fork.c b/sys/kern/kern_fork.c
index 94b2553..de2c483 100644
--- a/sys/kern/kern_fork.c
+++ b/sys/kern/kern_fork.c
@@ -782,9 +782,6 @@ fork_exit(callout, arg, frame)
 	cpu_critical_fork_exit();
 	CTR3(KTR_PROC, "fork_exit: new thread %p (pid %d, %s)", td, p->p_pid,
 	    p->p_comm);
-	if (PCPU_GET(switchtime.sec) == 0)
-		binuptime(PCPU_PTR(switchtime));
-	PCPU_SET(switchticks, ticks);
 	mtx_unlock_spin(&sched_lock);
 
 	/*
diff --git a/sys/kern/kern_synch.c b/sys/kern/kern_synch.c
index 1b05640..c0bab3b 100644
--- a/sys/kern/kern_synch.c
+++ b/sys/kern/kern_synch.c
@@ -506,22 +506,16 @@ mi_switch(void)
 	 */
 	cnt.v_swtch++;
 	PCPU_SET(switchtime, new_switchtime);
+	PCPU_SET(switchticks, ticks);
 	CTR3(KTR_PROC, "mi_switch: old thread %p (pid %d, %s)", td, p->p_pid,
 	    p->p_comm);
 	if (td->td_proc->p_flag & P_SA)
 		thread_switchout(td);
 	sched_switch(td);
 
-	/* 
-	 * Start setting up stats etc. for the incoming thread.
-	 * Similar code in fork_exit() is returned to by cpu_switch()
-	 * in the case of a new thread/process.
-	 */
 	CTR3(KTR_PROC, "mi_switch: new thread %p (pid %d, %s)", td, p->p_pid,
 	    p->p_comm);
-	if (PCPU_GET(switchtime.sec) == 0)
-		binuptime(PCPU_PTR(switchtime));
-	PCPU_SET(switchticks, ticks);
+
 	/* 
 	 * If the last thread was exiting, finish cleaning it up.
 	 */