[Beowulf] Re: Estimating cluster power consumption - more on I/O issues / Mr. Hahn

Ed Karns edkarns at firewirestuff.com
Wed Dec 21 10:13:20 PST 2005

On Dec 20, 2005, at 8:55 PM, Mark Hahn wrote:

>> extraneous video, I/O, drives and other bus linked hardware and
>> features, likewise ... improves performance. (I notice that some
>> performance system builders also fail to "disable" many built-in
>> features in CMOS BIOS setup ... thus unknowingly degrading
>> processor / bus performance.)
> I'm a DIY/minimalist myself, but have never been able to measure
> any real benefit.  what are these bios features or extraneous drivers
> that degrade performance?  saving some KB is not a bad thing, but...

Well, all extraneous I/O of almost any unneeded type should be  
disabled, regardless:

Example: if the nodes are to be connected via 1000baseT (PCI / PCI- 
extreme / PCMCIA plugin add on cards) and onboard built in LAN  
connectors are 100baseT and thus, not used then it should be obvious,  
but sometimes overlooked, that processor bus communications and  
performance are enhanced by disabling these extra LAN connections.  
Not only do these connections "steal" CPU cycles via interrupt IRQ  
polling, having the CPU spend time generating a default networking  
protocol on the built in LAN chip via this connection certainly does  
"steal" a whole lot of CPU time. (On a higher level, multiple  
protocols on the same LAN connections should likewise be removed or  

Example: Some nodes may have built in audio features. Although these  
may not prove to be net performance detractors in some cases,  
reliability may be enhanced by disabling these aka the KISS  
principle. (Consider: Newbe SysOps may wish to play MP3 files while a  
node is active.)

Example: depending on the CMOS / BIOS maker, the built in serial and  
parallel ports actually can steal CPU cycles if not disabled ... even  
on very modern x86 systems, these interrupt IRQs are still "polled"  
for activity unless disabled. (Note that some CMOS / BIOS routines  
that may indicate "disabled" in the setup are actually simply  
"blocked", the CMOS / BIOS may still be examining or polling the  
interrupt / IRQ. For those purists concerned about such CPU cycle  
theft, the BIOS might have to be completely rewritten or a substitute  
made to maximize CPU performance. [ala The Bill Gates Syndrome = what  
does IRQ 11 actually do?] )

Ed Karns

USBStuff / FireWireStuff / WireLessStuf / FiberStuf ... and much more


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