amd64/117664: iostat can't display IO current vlaue in first line

[John Baldwin]

On Tuesday 30 October 2007 03:22:39 am chifeng wrote:
> 
> >Number:         117664
> >Category:       amd64
> >Synopsis:       iostat can't display IO current vlaue in first line
> >Confidential:   no
> >Severity:       non-critical
> >Priority:       low
> >Responsible:    freebsd-amd64
> >State:          open
> >Quarter:        
> >Keywords:       
> >Date-Required:
> >Class:          change-request
> >Submitter-Id:   current-users
> >Arrival-Date:   Tue Oct 30 07:30:02 UTC 2007
> >Closed-Date:
> >Last-Modified:
> >Originator:     chifeng
> >Release:        FreeBSD6.2-Release-p8
> >Organization:
> Platform Computing
> >Environment:
> FreeBSD cnxabuild.asia.corp.platform.com 6.2-RELEASE-p8 FreeBSD 
6.2-RELEASE-p8 #0: Tue Oct 16 12:32:14 CST 2007     
root at xabuild.asia.corp.platform.com:/usr/obj/usr/src/sys/PLATFORM  amd64
> >Description:
> When I write a shell script plugin for munin, I hope get a current value of 
IO statistics. But iostat can't do it, it first statistics that are printed 
are avaraged over the system uptime. If I use "iostat -c 2 | tail -1 " 
command, this will wait 2s at least. 
> so I think for iostat first line, 1) iostat should be display current value, 
2) have a parameter to display current value at least. 

There isn't a 'current value' for iostat to dump.  The kernel just keeps 
running counts and iostat simulates a current value by saving the values each 
time and computing a delta for each line after the first.  However, for the 
first line there is no saved value so it cannot compute a delta.  Probably 
you need to write your own plugin that saves the previous values and computes 
deltas when queried similar to how iostat behaves.

-- 
John Baldwin