[osol-discuss] finding iowait processes

[Johan Hartzenberg]

On Mon, Jan 5, 2009 at 11:28 AM, Johan Hartzenberg <jhartzen at gmail.com>wrote:

>
>
> On Mon, Jan 5, 2009 at 11:08 AM, <Casper.Dik at sun.com> wrote:
>
>>
>> >Hi,
>> >
>> >Is there a way to find processes that makes the most iowait in system?
>> >iostat -xtc and iostat commands shows me that the system in iowait
>> >state but I need to find out which processes cause that..
>> >
>>
>>
>> iowait on OpenSolaris?  AFAIK, "I/O wait" was removed from Solaris 10
>> before it was released; it's therefor also not in OpenSolaris.
>>
>> Casper
>>
>>
> Hello Casper,
>
> Please educate me:  I missed the "io-wait" values for a long time.  Then I
> thought I started to understand the reason why the metric was deemed
> invalid:  While one process is blocked, any other process which is not
> blocked can use the CPU.  Thus the CPU is just idle, not "waiting on IO".
>
> Conversely, I understand that while there is no specific "IO-wait" status
> for the system (or a CPU), a specific Process can still be waiting for IO?
>
> My understanding is that the reason why the metric is deemed meaningless is
> because it was reported against system resources (Eg a CPU) in stead of
> against a specific process.  So the question is "how do you identify which
> processes are blocking on IO" (or page-in, or ...)
>
> Or better:  How do you know how much each process is blocking?
>
> Thanx,
>   _Johan
>
>
In the dtrace manual here:
http://docs.sun.com/app/docs/doc/819-5488/gbxwz?a=view


I found this paragraph:

 cpu_ticks_wait

Probe that fires when the periodic system clock has made the determination
that a CPU is otherwise idle, but some threads are waiting for I/O on the
CPU. This probe fires in the context of the system clock and therefore fires
on the CPU running the system clock. The cpu_t argument (arg2) indicates the
CPU that has been deemed waiting on I/O.

So how do I identify the corresponding process, and how do I determine how
many of those tics belongs to each of those "waiting" processes?

Thanx,
  _Johan


-- 
Any sufficiently advanced technology is indistinguishable from magic.
   Arthur C. Clarke

My blog: http://initialprogramload.blogspot.com
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