Run a revision of the devstat interface:

Kernel:

Change statistics to use the *uptime() timescale (ie: relative to
boottime) rather than the UTC aligned timescale.  This makes the
device statistics code oblivious to clock steps.

Change timestamps to bintime format, they are cheaper.

Remove the "busy_count", and replace it with two counter fields:
"start_count" and "end_count", which are updated in the down and
up paths respectively.  This removes the locking constraint on
devstat.

Add a timestamp argument to devstat_start_transaction(), this will
normally be a timestamp set by the *_bio() function in bp->bio_t0.
Use this field to calculate duration of I/O operations.

Add two timestamp arguments to devstat_end_transaction(), one is
the current time, a NULL pointer means "take timestamp yourself",
the other is the timestamp of when this transaction started (see
above).

Change calculation of busy_time to operate on "the salami principle":
Only when we are idle, which we can determine by the start+end
counts being identical, do we update the "busy_from" field in the
down path.  In the up path we accumulate the timeslice in busy_time
and update busy_from.

Change the byte_* and num_* fields into two arrays: bytes[] and
operations[].

Userland:

Change the misleading "busy_time" name to be called "snap_time" and
make the time long double since that is what most users need anyway,
fill it using clock_gettime(CLOCK_MONOTONIC) to put it on the same
timescale as the kernel fields.

Change devstat_compute_etime() to operate on struct bintime.

Remove the version 2 legacy interface: the change to bintime makes
compatibility far too expensive.

Fix a bug in systat's "vm" page where boot relative busy times would
be bogus.

Bump __FreeBSD_version to 500107

Review & Collaboration by:	ken

1 files changed, 5 insertions, 7 deletions

diff --git a/usr.sbin/iostat/iostat.c b/usr.sbin/iostat/iostat.c
index 3370df2..724756e 100644
--- a/usr.sbin/iostat/iostat.c
+++ b/usr.sbin/iostat/iostat.c
@@ -407,12 +407,10 @@ main(int argc, char **argv)
 	cur.tk_nin = 0;
 
 	/*
-	 * Set the busy time to the system boot time, so the stats are
-	 * calculated since system boot.
+	 * Set the snap time to the system boot time (ie: zero), so the 
+	 * stats are calculated since system boot.
 	 */
-	if (readvar(kd, "kern.boottime", X_BOOTTIME, &cur.busy_time,
-		    sizeof(cur.busy_time)) != 0)
-		exit(1);
+	cur.snap_time = 0;
 
 	/*
 	 * If the user stops the program (control-Z) and then resumes it,
@@ -452,7 +450,7 @@ main(int argc, char **argv)
 		last.dinfo = cur.dinfo;
 		cur.dinfo = tmp_dinfo;
 
-		last.busy_time = cur.busy_time;
+		last.snap_time = cur.snap_time;
 
 		/*
 		 * Here what we want to do is refresh our device stats.
@@ -538,7 +536,7 @@ main(int argc, char **argv)
 			last.tk_nout = tmp;
 		}
 
-		etime = devstat_compute_etime(cur.busy_time, last.busy_time);
+		etime = cur.snap_time - last.snap_time;
 
 		if (etime == 0.0)
 			etime = 1.0;