[Info-vax] What choices are available to the OpenVMS Process Scheduler once all the CPUs are in use?

[Kerry Main]

> -----Original Message-----
> From: Info-vax [mailto:info-vax-bounces at info-vax.com] On Behalf Of
> Carl Friedberg via Info-vax
> Sent: 10-Feb-16 2:28 PM
> To: info-vax at info-vax.com
> Cc: Carl Friedberg <frida.fried at gmail.com>
> Subject: Re: [New Info-vax] What choices are available to the OpenVMS
> Process Scheduler once all the CPUs are in use?
> 
> Of course I know the 782 was ASMP, that was a (bad) joke. Hyper-
> threading
> is a nice way to up the marketing value by doubling the number of core
> CPUs, but I doubt that VMS users will see much, if any benefit; and
> possibly there will be a performance penalty. It can't hurt to test a
> specific environment, as it would be hard to predict IMO.
> 
> Whatever the benefit of hyper-threading, I doubt anyone will ever
> double
> their throughput by turning it on. YMMV.
> 
> Carl

[snip..]

It's not just OpenVMS that sees little benefit with threads, the same
is (mostly) true of other platforms. As I recall, the standard feedback
from MS on the latest Windows Server versions is leave threads off.

When you mix threads with NUMA (most server HW today is NUMA 
based - incl x86-64) and local vs. remote memory, to me, there is just
way to many ways for things to go wrong performance wise.

To be fair - I did do a DC project last year where they were heavy users 
of Solaris on the relatively current M5 SPARC servers. Their app was a 
huge web site with lots of parallel independent web requests and they 
used threads extensively. The M5 allowed up to 8 threads per core, but 
the HW and OS were both designed to support these concurrent threads.
(case of single vendor making HW + OS ..remember the good old days?)

Generally speaking, the target perf range for servers is typically 60-80% 
utilization in peak times. Since even with best case you are only going to 
get single digit perf increases, there are likely better ways to get better 
performance - like App/DB tuning. 

Regards,

Kerry Main
Kerry dot main at starkgaming dot com