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

3 files changed, 17 insertions, 17 deletions

diff --git a/usr.bin/systat/iostat.c b/usr.bin/systat/iostat.c
index ba39f3e..a54bb6d 100644
--- a/usr.bin/systat/iostat.c
+++ b/usr.bin/systat/iostat.c
@@ -148,8 +148,6 @@ fetchiostat()
 	last.dinfo = cur.dinfo;
 	cur.dinfo = tmp_dinfo;
          
-	last.busy_time = cur.busy_time;
-
 	/*
 	 * Here what we want to do is refresh our device stats.
 	 * getdevs() returns 1 when the device list has changed.
@@ -322,7 +320,7 @@ devstats(row, _col, dn)
 	
 	di = dev_select[dn].position;
 
-	busy_seconds = devstat_compute_etime(cur.busy_time, last.busy_time);
+	busy_seconds = cur.snap_time - last.snap_time;
 
 	if (devstat_compute_statistics(&cur.dinfo->devices[di],
 	    &last.dinfo->devices[di], busy_seconds,
diff --git a/usr.bin/systat/vmstat.c b/usr.bin/systat/vmstat.c
index 5fc1985..ff7a37b 100644
--- a/usr.bin/systat/vmstat.c
+++ b/usr.bin/systat/vmstat.c
@@ -798,7 +798,7 @@ getinfo(ls)
 	last.dinfo = cur.dinfo;
 	cur.dinfo = tmp_dinfo;
 
-	last.busy_time = cur.busy_time;
+	last.snap_time = cur.snap_time;
 	switch (devstat_getdevs(NULL, &cur)) {
 	case -1:
 		errx(1, "%s", devstat_errbuf);
@@ -852,12 +852,19 @@ dinfo(dn, lc, now, then)
 
 	di = dev_select[dn].position;
 
-	elapsed_time = devstat_compute_etime(now->busy_time,
-	    then ? then->busy_time : now->dinfo->devices[di].dev_creation_time);
-
-	device_busy =  devstat_compute_etime(now->dinfo->devices[di].busy_time,
-	    then ? then->dinfo->devices[di].busy_time :
-	    now->dinfo->devices[di].dev_creation_time);
+	if (then != NULL) {
+		/* Calculate relative to previous sample */
+		elapsed_time = now->snap_time - then->snap_time;
+		device_busy = devstat_compute_etime(
+		    &now->dinfo->devices[di].busy_time,
+		    &then->dinfo->devices[di].busy_time);
+	} else {
+		/* Calculate relative to device creation */
+	        elapsed_time = now->snap_time - devstat_compute_etime(
+		    &now->dinfo->devices[di].creation_time, NULL);
+		device_busy = devstat_compute_etime(
+		    &now->dinfo->devices[di].busy_time, NULL);
+	}
 
 	if (devstat_compute_statistics(&now->dinfo->devices[di], then ?
 	    &then->dinfo->devices[di] : NULL, elapsed_time,
@@ -866,11 +873,6 @@ dinfo(dn, lc, now, then)
 	    DSM_NONE) != 0)
 		errx(1, "%s", devstat_errbuf);
 
-	if ((device_busy == 0) && (transfers_per_second > 5))
-		/* the device has been 100% busy, fake it because
-		 * as long as the device is 100% busy the busy_time
-		 * field in the devstat struct is not updated */
-		device_busy = elapsed_time;
 	if (device_busy > elapsed_time)
 		/* this normally happens after one or more periods
 		 * where the device has been 100% busy, correct it */
diff --git a/usr.bin/vmstat/vmstat.c b/usr.bin/vmstat/vmstat.c
index fb99b2c..88c1d21 100644
--- a/usr.bin/vmstat/vmstat.c
+++ b/usr.bin/vmstat/vmstat.c
@@ -428,7 +428,7 @@ dovmstat(interval, reps)
 		tmp_dinfo = last.dinfo;
 		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.
@@ -680,7 +680,7 @@ devstats()
 		last.cp_time[state] = tmp;
 	}
 
-	busy_seconds = devstat_compute_etime(cur.busy_time, last.busy_time);
+	busy_seconds = cur.snap_time - last.snap_time;
 
 	for (dn = 0; dn < num_devices; dn++) {
 		int di;