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Subject: msps from iostat is wrong 
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>Number:         18114
>Category:       bin
>Synopsis:       iostat(8): msps from iostat is wrong
>Confidential:   no
>Severity:       non-critical
>Priority:       low
>Responsible:    freebsd-bugs
>State:          closed
>Quarter:        
>Keywords:       
>Date-Required:  
>Class:          sw-bug
>Submitter-Id:   current-users
>Arrival-Date:   Thu Apr 20 06:50:01 PDT 2000
>Closed-Date:    Mon Oct 18 00:25:39 UTC 2010
>Last-Modified:  Mon Oct 18 00:25:39 UTC 2010
>Originator:     Elias A. Argenton
>Release:        FreeBSD 3.4-RELEASE i386
>Organization:
   PROCERGS - Companhia de Processamento de Dados do Estado do Rio Grande do Sul
>Environment:

	
   Intel dual Pentium III 500 MHz

>Description:

	
   The report of msps from iostat don't correspond to stated in man page.
This is a sample of the output from "iostat  -t da  -w 5  -do"
         da0           da1
sps tps msps  sps tps msps
490  41 24.7  107   6   179
559  51 19.6   94   5   218
513  37 27.2  154   6   179
166  18 56.3   26   1  1253
291  28 36.3   32   2   418
158  12 80.8   10   1  1670
156  13 74.8   29   0  2505
313  25 40.7   28   0  2505
101  10 98.2    0   0   0.0
160  15 65.1   13   1  1253
304  23 43.2   94   4   250
118  10  104    3   0  5010
 47   6  179    0   0   0.0
202  17 59.6  185   2   501
169  12 83.5    0   0   0.0
111   7  152    0   0   0.0
464  22 45.1    0   0   0.0
330  26 39.1   54   2   455

Multiplying tps by msps for da0 we obtain the following numbers:
average=1009ms; min=969ms; max=1074 ms. 
This seems to me that msps is not a real measurement but instead, is
   derived mathematicaly from 1/tps (1 second divided by tps number).
Howhever we need a real msps measurement to know how our disks are
   doing their job.


>How-To-Repeat:

	
execute the command "iostat  -t da  -w 5  -do" and see the results.

>Fix:
	
	


>Release-Note:
>Audit-Trail:
Responsible-Changed-From-To: gnats-admin->freebsd-bugs 
Responsible-Changed-By: asmodai 
Responsible-Changed-When: Sun Apr 30 06:38:31 PDT 2000 
Responsible-Changed-Why:  
Misfiled PR. 
State-Changed-From-To: open->suspended 
State-Changed-By: ken 
State-Changed-When: Sun Apr 30 21:13:17 PDT 2000 
State-Changed-Why:  
We don't actually measure the time per transaction in the kernel, so it 
isn't really possible to give the user a "real" time per transaction 
number.  The number we print out is an average time per transaction, 
derived as the submitter guessed from the number of transactions in the 
measurement period and the measurement period itself.  There has been 
talk about doing a kernel facility to measure the time per transaction, 
but I don't expect it to happen any time soon.  So I'm leaving this PR 
in the suspended state in case I decide to do a facility to measure the 
time per transaction at some point in the future. 


Responsible-Changed-From-To: freebsd-bugs->ken 
Responsible-Changed-By: ken 
Responsible-Changed-When: Sun Apr 30 21:13:17 PDT 2000 
Responsible-Changed-Why:  
I'm the iostat maintainer. 
Responsible-Changed-From-To: ken->freebsd-bugs 
Responsible-Changed-By: linimon 
Responsible-Changed-When: Thu Aug 2 00:38:12 UTC 2007 
Responsible-Changed-Why:  
With permission, reassign away from inactive committer. 

http://www.freebsd.org/cgi/query-pr.cgi?pr=18114 
State-Changed-From-To: suspended->feedback 
State-Changed-By: arundel 
State-Changed-When: Tue Oct 5 21:05:01 UTC 2010 
State-Changed-Why:  
After some research in connection with this PR I believe it can be closed. 
Revision r81134 (from Aug 2001) switched from compute_stats(3) to 
devstat_compute_statistics(3). With this change a lot of 'real' kernel stats 
could be accessed from within iostat(8). One of these stats is: 

" 
DSM_MS_PER_TRANSACTION_FREE     type: long double * 

The average duration of transactions of 
the specified type between the acquisi- 
tion of previous and current. 
" 

This means that 'msps' is now being derived from actual kernel stats and no 
longer from 'tps'. 
Since this is such an old PR and I'm not 100% sure I got this right, I'm keeping 
it in feedback state until somebody can verify or falsify my assumption. 

Cheers. 
Alex 

http://www.freebsd.org/cgi/query-pr.cgi?pr=18114 
State-Changed-From-To: feedback->closed 
State-Changed-By: arundel 
State-Changed-When: Mon Oct 18 00:23:40 UTC 2010 
State-Changed-Why:  
Since nobody seemed to disagree with my assumption, go ahead and close this PR. 

http://www.freebsd.org/cgi/query-pr.cgi?pr=18114 
>Unformatted:
