[THIN] Re: latency

  • From: "Braebaum, Neil" <neil.braebaum@xxxxxxxxxxxxxxxxxxxxxxxx>
  • To: "'thin@xxxxxxxxxxxxx'" <thin@xxxxxxxxxxxxx>
  • Date: Fri, 4 Oct 2002 09:36:43 +0100

Bernd

Just to clarify - are you suggesting there are circumstances where counters
are not reporting, or not accounting for system / kernel activity (ie that
it is being underreported)?

Or merely that this information is somewhat obfuscated?

I find it difficult to believe that system / kernel activity is effectively
black-holing from a reporting / monitoring perspective - be it from task
manager, or perfmon.

I'd agree that system / kernel activity can be difficult to track down
exactly as to the cause, but I've *never* encountered scenarios where the
system has busy cpus, but misleading counters - except for when a machine is
so obviously *so* busy, that the monitoring application / utility isn't
getting a look in.

Neil

> -----Original Message-----
> From: Bernd Harzog [mailto:bernd@xxxxxxxxxxx] 
> Sent: 03 October 2002 22:32
> To: thin@xxxxxxxxxxxxx
> Subject: [THIN] Re: latency
> 
> The behavior that Eric describes is very interesting. The 
> important point is a drop in CPU utilization when the latency 
> occurs. What this means is two things; 1) The CPU utilization 
> counter is not measuring whatever is causing the latency, 2) 
> Something is causing the CPU to spend a lot of time doing 
> something instead of useful work on behalf of user applications.
> 
> There is a scenario which we have encountered at customers 
> which fits into the above explanation. That scenario is that 
> the time that the CPU spends on certain system level 
> operations (kernel mode operations like Page File Writes, and 
> Page Faults) is not counted by the CPU utilization counter, 
> AND that something is making the CPU spend a lot of time 
> these Kernel Mode operations. The things that can cause these 
> kinds of Kernel Mode operations to block useful work include 
> a saturated disk driver, a large number of queued up page 
> writes, a large number of page faults and numerous other things.
> 
> If you are experiencing this kind of behavior, and it is 
> being caused by excessive paging (watch page file writes in 
> Perfmon), then TSCale will help. If you are saturating your 
> RAID drivers TScale cannot help.

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