Sybase on UltraSPARC IV
Per Eirik
each physical CPU act as two logical CPUs to the OS:
http://www.sun.com/servers/highend/whitepapers/Sun_Fire_Enterprise_Servers_Performance.pdf
I have heard that Sybase UK claims that you have to buy two Internet Access
Licences for each UltraSPARC IV CPU because it acts as two CPUs to the OS.
Can this really be true?
In case, is it possible to turn off Chip Multi-Threading on Sun/Solaris
servers?
I think CMT is comparable to Hyperthreading on Intel XEON CPUs. Sybase
recommends that Hyperthreading should be turned off to maximize Sybase
performance on Linux, see page 3:
http://www.sybase.com/content/1025313/linux_optimizing_performance_wp.pdf
Would that also be the case for UltraSPARC IV processors?
Thanks!
Per Eirik
(remove all underscores in email address)
Anton Rang
> Sun's new UltraSPARC IV processor supports Chip Multi-Threading (CMT) where
> each physical CPU act as two logical CPUs to the OS [...]:
>
> I have heard that Sybase UK claims that you have to buy two Internet Access
> Licences for each UltraSPARC IV CPU because it acts as two CPUs to the OS.
> Can this really be true?
It would depend on Sybase's licensing model. They might choose to
make you purchase two licenses for an UltraSPARC IV, since it is
roughly twice as fast as an UltraSPARC III....
> In case, is it possible to turn off Chip Multi-Threading on Sun/Solaris
> servers?
Well, you can disable a processor core using 'psrset' but then you
aren't using half of the machine that you bought.
> I think CMT is comparable to Hyperthreading on Intel XEON CPUs.
No, it's quite different.
A hyperthreaded Intel CPU has a single processor core which
alternately issues instructions from two threads (the details are more
complex, but that's the rough idea). Once the instructions from the
two threads have been issued, the single processor core executes them
together, possibly simultaneously if enough resources are available.
An UltraSPARC IV, like a POWER 4, has two separate processor cores.
They each run one thread. In many ways, it's like having two entirely
independent processors, just glued together into one chip.
> Sybase recommends that Hyperthreading should be turned off to
> maximize Sybase performance [ ... ]
> Would that also be the case for UltraSPARC IV processors?
No.
On the Xeon, you want hyperthreading disabled because most of the
threads are doing database work, and would be competing for the same
set of processor resources -- having two database threads in the
processor at once would just slow both of them down.
On the SPARC, you want both processor cores enabled because they each
have a complete set of resources [*] and would both be doing useful
work on a database thread. Given two threads, they'll run very nearly
twice as fast as a single thread.
-- Anton
(Disclaimer: I work for Sun, albeit not in the processor or systems group.)
[*] There are a few resources shared, notably the system bus interface
and the cache. However, the system bus interface supports several
outstanding transactions, so it's unlikely to be a bottleneck. The
cache could be, but two database threads are likely to be accessing
many of the same areas in memory, so the shared cache might actually
be a net win here, or at least a wash.
Casper H.S. Dik
>> I think CMT is comparable to Hyperthreading on Intel XEON CPUs. Sybase
>> recommends that Hyperthreading should be turned off to maximize Sybase
>> performance on Linux, see page 3:
>>
>> http://www.sybase.com/content/1025313/linux_optimizing_performance_wp.pdf
>>
>> Would that also be the case for UltraSPARC IV processors?
No, Hyperthreading and UltraSPARC IV CMT are not the same thing; the
UltraSPARC IV is two CPUs on a single die with some cache bits shared.
The performance is comparable to two independent CPUs.
Hyperthreading shares most of the CPU real estate; the maximum performance
gain is a few percentage points and a for certain workloads there's
a performance loss.
Casper
--
Expressed in this posting are my opinions. They are in no way related
to opinions held by my employer, Sun Microsystems.
Statements on Sun products included here are not gospel and may
be fiction rather than truth.
noone
> Per Eirik wrote:
>
>>Suns new UltraSPARC IV processor supports Chip Multi-Threading (CMT) where
>>each physical CPU act as two logical CPUs to the OS:
>>
>>http://www.sun.com/servers/highend/whitepapers/Sun_Fire_Enterprise_Servers_Performance.pdf
>>
>>I have heard that Sybase UK claims that you have to buy two Internet Access
>>Licences for each UltraSPARC IV CPU because it acts as two CPUs to the OS.
>>Can this really be true?
>
>
> But, if its one physical CPU, I don't see how they can charge you
> a license for two (assuming your licensing is CPU based). Regardless,
> an Internet Access license isn't dependant on the number of CPUs
> (or is it?).
It is ...e.g. We have an Internet Access license ( IAL ) for 6 CPUs on
an E3500, and another IAL for 2 CPUs on a SunFire 280R.