Handled no difference in seek times

For some reason recent kernels (2.6.25.4, for example) have lost a lot of resolution in our blktrace times. This can result in lots of things happening "simultaneously." This change at least tries to handle the case where all the seeks happen at once.

Probably have other issues that need to be looked into...

[[Jens: I've pushed this, so you don't need to apply this, but I'm wondering have others seen this? I'm seeing 0.01 - which I think means we're gated by HZ (set to 100 on this .config, I'm trying w/ HZ00 to check this theory). A /lot/ happens in 1/100th of a second on modern computers! :-) ]]

---
 btt/doc/btt.tex |    4 +++-
 btt/seek.c      |    7 ++++---
 2 files changed, 7 insertions(+), 4 deletions(-)

index 9938f67..87e7082 100644
@@ -769,7 +769,9 @@ Device:       rrqm/s   wrqm/s     r/s     w/s

rsec/s wsec/s

When there is only a single data point within a 1-second window, \texttt{btt} will just output the time value for the point, and the

-  value 1.0 in the second column.
+  value 1.0 in the second column. If there is no perceived difference
+  in the times present for the current sample, then the second columns
+  value is the number of seeks present at that time.

Otherwise, if $\alpha$ and $\Omega$ are the first and last times seen within a 1-second window, and $\nu$ are the number of seeks seen

index fec57c4..69400c8 100644
@@ -18,6 +18,7 @@
  *  Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA

02111-1307 USA
*
*/
+#include <float.h>
#include "globals.h"

static struct file_info *seek_files = NULL;
@@ -102,13 +103,13 @@ static void sps_emit(struct seeki *sip)
{
double tstamp, s_p_s;
struct sps_bkt *sps = &sip->sps;
+ double delta = sps->t_last - sps->t_start;

- if (sps->nseeks = 1) {
- s_p_s = 1.0;
+ if ((sps->nseeks = 1) || (delta < DBL_EPSILON)) {
+ s_p_s = (double)(sps->nseeks);
tstamp = sps->t_start;
}
else {
- double delta = sps->t_last - sps->t_start;

s_p_s = (double)(sps->nseeks) / delta; tstamp = sps->t_start + (delta / 2);

1.5.4.3

Hm, might just be my testbed - I'm getting:

[    6.665781] Clocksource tsc unstable (delta = 88002879 ns)

in dmesg, and looking at the code I /think/ this drops the high res timer off.

<sigh>
Alan