Re: Diagnose high wait

[Harder, Pieter]

Just to give an extreme example from another time, another galaxy. I had a 
z9-BC (I told you, long ago) with TSM Linux VM (Tivoli Storage Manager, the 
backup thingy) that moved data for replication purposes from a TS3500 to a 
TS3310 with six tape pairs. Reached almost 1 GB/s with very little CPU going 
on. You should have seen the wait on that. And yes, I used Barton's tooling to 
look at it together with Rob.

best regards,
Pieter Harder 

Van: Linux on 390 Port <LINUX-390@VM.MARIST.EDU> namens Mark Post 
<mp...@suse.com>
Verzonden: maandag 24 april 2017 20:36
Aan: LINUX-390@VM.MARIST.EDU
Onderwerp: Re: Diagnose high wait

>>> On 4/24/2017 at 04:34 AM, Christer Solskogen <christer.solsko...@gmail.com>
wrote:
> While we're at talking about high steal% , could somebody share some
> insights about how to diagnose high wait%?

On top of what Barton said, a high percent wait time can show up if a Linux 
system is using very little CPU time, but one or more tasks are doing a lot of 
I/O.  If the system is using a lot of CPU, then it's more likely what Barton is 
talking about.


Mark Post

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Re: Diagnose high wait

[Mark Post]

>>> On 4/24/2017 at 04:34 AM, Christer Solskogen 
wrote: 
> While we're at talking about high steal% , could somebody share some
> insights about how to diagnose high wait%?

On top of what Barton said, a high percent wait time can show up if a Linux 
system is using very little CPU time, but one or more tasks are doing a lot of 
I/O.  If the system is using a lot of CPU, then it's more likely what Barton is 
talking about.


Mark Post

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Re: Diagnose high wait

[Barton Robinson]

On our website,
"http://velocitysoftware.com/present/flowchrt.html; , there is a
performance analysis flow chart.  When there is wait, it is MOST often
not related to the linux server, it is MOST likely to be related to
resource constraints that the server just happens to be using (cpu,
storage/ram, paging, sometimes I/O...).
There is also a performance class
"http://velocitysoftware.com/seminar/workshop.html; june 19th in
Columbus just prior to the VM Workshop.  Or in the UK Nov 6th prior to
the UK GSE.


On 4/24/2017 1:34 AM, Christer Solskogen wrote:

While we're at talking about high steal% , could somebody share some
insights about how to diagnose high wait%?

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