ASE on Power8 / 16 Cpus + SMT8 ( 128 Vcpus)

[former_member261828]

Hi

I'm performing perfromance testing with ASE 15.7 / SP134 on AIX Power8. The machine has 16 Cores and SMT 8 is activated

ASE is configured with 'only' 64 'engines' (ie the thread pool syb_default_pool has 64 Threads) and aggressive tasks stealing is on.

The Idle Time out has been set to 2000.

When ASE activity reach 65%/70% the the spinlock contention on 'Sched Q' and 'Global Sched' reach respectively 52% and 50 %.

When agressive task stealing is Off the others spinlocks do not exceed 5%, so the real issue seems to be the  spinlocks on 'Sched Q' and 'Global Sched'

My questions are :

-What is part of this rate of spinlock activity on overall Engine % Usage ?  Is there any way to determine it or evaluate it ?

-What is maximum of 'Engine' (ie threads in syb_default_pool) we can have without having Sched Spinlock issue ?

-Will it behave differently with v16 ?

Thanks

Emmanuel

[former_member182259 · Accepted solution]

The problem is that the engines are largely idle - check monThreads - especially with idle timeout set that high.   I'd reduce idle timeout to 250 for a start.    When the engines are idle (no task in the global queue), they try to steal tasks from the other engine's local run queues and you see the spinlock contention you have.    It is perfectly fine to run with 'aggressive task stealing' turned off - in fact, especially when ASE's are sized for peak load and often run at considerably less and therefore a lot of idle time, it probably should be the setting.

[former_member261828 · Accepted solution]

Thanks Jeff I my case the threads User time reaches 60%/70% , so the engines are not excaclty idle.

My main question how Can I evaluate the rate or % of the spinlock activity on overall Engine % Usage ? 

Is there any way to determine it or evaluate it ?

[former_member182259 · Accepted solution]

30-40% Idle is still quite a bit (with large engine counts and aggressive task stealing enabled) and is precisely what I was saying.   But you really need to look at IdleTicks:BusyTicks and TotalTicks.

[former_member261828 · Accepted solution]

Ok thanks for your help

Rgds

Emmanuel