Date: Sat, 1 Sep 2001 21:02:51 -0600 From: Mike Porter <mupi@mknet.org> To: "Ted Mittelstaedt" <tedm@toybox.placo.com>, "Sean Chittenden" <sean@chittenden.org>, "Bsd Newbie" <bsdneophyte@yahoo.com> Cc: <freebsd-questions@freebsd.org> Subject: Re: overclocking and FreeBSD stablity... Message-ID: <200109020302.f8232pl07186@c1828785-a.saltlk1.ut.home.com> In-Reply-To: <00dc01c1329d$b0b523c0$1401a8c0@tedm.placo.com> References: <00dc01c1329d$b0b523c0$1401a8c0@tedm.placo.com>
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On Friday 31 August 2001 10:22 pm, Ted Mittelstaedt wrote: > >-----Original Message----- > > From: owner-freebsd-questions@FreeBSD.ORG > > >[mailto:owner-freebsd-questions@FreeBSD.ORG]On Behalf Of Sean Chittenden > > > >Slowaris wasn't meant to be a performance system and probably chokes > >when it runs at speeds above 400Mhz. > > Solaris runs fine on our Compaq 550Mhz system. > > My $0.02 is that the base of the troubles is the machine code that the > compiler produces. I suspect that when a CPU is overclocked that unless > the parts are good that the CPU is unable to execute SOME of it's opcodes, > opcodes that produce certain electrical patterns inside of the CPU that > may ring and generate electrical wave colissions. While I'm not an EE > I do know that lengths of traces and such inside of a CPU are held to > precise tolerances in order to deal with clock propagations and such. It's > not just the cooling but when you overclock the CPU you can have signals > arriving at internal parts of the CPU earlier than the designer intended. > What you fail to realize in this is two things. First, the designers of processors measure everything in terms of clock cycles rather than other, more objective, standards. So for a signal to arrive at its destination "earlier than intended" the various parts of the CPU have to be operating at different clock speeds. This applies to die sizes much smaller than those currently in use and to clock speeds much higher than those currently in use. Eventually, yes, that will be a problem, but not until frequencies with wavelengths smaller than the internal pathways of the chips (hint: we ain't there yet...you'll fry your chip (or turn it into something resembling the Vegas strip, at least) before you'll reach that threshold). Second, and this is the primary reason people overclock, is the *method* used to determine what clock speed a chip is capable of. (and this varies by product and manufacturer, of course, but we'll stick with Intel for the time being). When intel makes a chip, it is part of a wafer, which has several (as many as 10-12, depending on what they are building) chips. This entire wafer is tested to determine the maximum clock speed every chip in the wafer will run reliably at. This is based on a number of factors, including the maximum clock speed they are currently building for that product line, and other stuff. If EVERY chip in the wafer passes at the maximum clock speed, then the entrie wafer is packaged as that clock speed. If one (or more) of the chips FAILS, however, they step down to the next clock speed, and try again. If every chip on the wafer passes at that clock speed, they mark the WAFER as that clock speed. But you have a one-in-twleve (if there are 12 chips on a wafer) chance of a CPU that is really capable of the fastest clock speed for that chip design. This process continues until they reach a clock speed at which all of the chips pass, or they reach a "bottom" threshold where the cost of producing the chips has exceeded the revenue they will get, and they throw the wafer away. So for any given clock speed marked below the maximum clock speed for that family, you have pretty decent chance of having a chip which can run significantly faster than the marked speed, up to the maximum spped for which they are marking chips. (of course, you may be able to go faster than that, but in that case, you really are taking a chance). The other wrinkle in this scheme is that Intel is completely free, if the demand is there, to remark their OWN chips to a LOWER speed. So if demand spikes for a 300Mhz Celeron, and they have a pile of 450Mhz Celerons sitting on the shelf, there is nothing illegal, immoral, or fattening about calling them 300Mhz Celerons and pricing them accordingly. (after all, they passed as 450Mhz celerons..and don't forget, any given chip in the lot of 450's has a one-in-ten or so chance of being capable of much faster speeds than even 450Mhz). (this second argument, BTW, pretty much nullifies the "design" argument by itself, since all chips are "designed" to be the fastest speed in their family) Of course, your mileage may vary, and if your luck is like mine, you will get the *one* 300MHz part that made the wafer fail, and be unable to overclock at all, and everyone else will sail along at 600Mhz or so with no problems.... The other wrinkle is that your motherboard may not be able to handle overclocking correctly: if they follow Intel's instructions properly, for example, without considerable effort, you can't change the multiplier. This means that to overclock, you must also run the motherboard faster than intended. And the distances involved on a motherboard *are* longer than a 100Mhz wavelength, which can cause all sorts of problems, if your motherboard will even allow you to. Then all of your peripherals have to support the higher clock speeds, becuase all the motherboard does is count 3 100Mhz clocks and produce a 33Mhz clock for your PCI bus....but if you are counting 3 109Mhz clocks, suddenly you get a 36Mhz clock, and THOSE components may or may not support running that fast.. ..if your network card, for example, relies on a 33Mhz PCI clock to generate the 20Mhz 10Base-T carrier, and your 33Mhz clock is off....you might not be able to talk on the network. (fortuneately, most network cards don't do this, they have their own 20Mhz crystal for that; it's more reliable...but...if your network card heats up more than normal becuase it is running faster than normal (more clocks=more work=more heat) then that will screw up the crystal, too, and might make you unable to talk on the network...or worse, abnle to talk on the network when you fire up your computer in the morning, but not when you come back from lunch in the afternoon, until you shut your computer off overnight, and it cools down, and starts talking again.....try troubleshooting THAT one!) > Certainly, you can overclock to a certain extent because most electrical > parts are derated somewhat. But there are just so many variables that > you can't just make blanket statements about overclocking. > That is certainly true. Even with identical hardware, as I mentioned above, becuase of quality control, you may or may not get the same results as the next guy. HOWEVER....software shouldn't affect it all that much except in one area (granted this is a big concern for overclockers anyway): heat. If your compiler produces better code than the other guy's it will run more efficiently on your hardware, and generate less heat. If you are overclocking to the point of bordeline failure (say, running a processor above the speed at which it actually failed intel's tests, but it works ok), this can make a difference. If you are less efficient than the other guys, then you just might push the processor over the edge into total failure. The moral of the story: if you can't afford to replace your processor, don't overclock. If you have money to burn, then its your business, but I might suggest either 1) buying a faster processor to start with and/or 2) contributing to the freeBSD project <(}; mike To Unsubscribe: send mail to majordomo@FreeBSD.org with "unsubscribe freebsd-questions" in the body of the message
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