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A8V Deluxe memory settings
A8V Deluxe memory settings in bios has "Scrub" settings disabled.
Should these be enabled for better performance ? 2 512 pc3200 in Dual Channel Mode. Thanks Ron |
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In article , "RonK"
wrote: A8V Deluxe memory settings in bios has "Scrub" settings disabled. Should these be enabled for better performance ? 2 512 pc3200 in Dual Channel Mode. Thanks Ron Some memory controllers support ECC error detection and correction. You need DIMMs with a 72 bit wide data path (an ECC DIMM) to talk to the 72 bit wide memory bus on an ECC equipped memory controller. Now, that being said, there are two ways for ECC to be used. When ECC is enabled, it means on every write, a whole 72 bit word, with a valid ECC, are written to memory. If an architecture supports byte or half word operands, to update a location in memory, while ECC is enabled, means reading the whole 72 bit quantity, replacing the section of the word to be updated, then writing the data back. (A read-modify-write cycle, instead of just a write cycle, when ECC is enabled. That is needed in order to update the ECC byte in the memory location.) Depending on how often the archtecture does that, determines how much performance is lost while using ECC. A second way ECC can be used, is to "audit" the contents of the entire memory. When "scrub" is enabled, the memory controller does some independent accesses of the memory, in an incrementing address pattern. If a memory read error is correctable, the memory controller writes back the content of the memory, and attempts to correct the data, based on the error syndrome. If the memory read error is uncorrectable, then the scrubber could report the serious error condition to the OS (and I don't know how a scrubbed memory error is treated, as the memory being tested might not currently be used by the OS). By moving through memory, and correcting the easy to correct errors, the error rate of the memory is reduced. In other words, when the OS fetches from a scrubbed location later, the OS could be blissfully unaware that the location had a simple error in it previously, since the scrubber already corrected it. This is good if the memory errors are caused by alpha radiation in the memory chip packaging (not as much of an issue as it once was). This is a useful function in mission critical server applications, and presumably ECC was added to the architecture for the sake of the Opteron family and its server applications. Whether it buys you anything in a desktop application is questionable. For a desktop, if you've already tested the computer with memtest86 and Prime95, your chances of seeing an error are pretty slim. You are likely to be rebooting often enough, that error accumulation is a non issue. Before enabling scrubbing, you may want to do more research on some of the private forums, as scrubbing implementations haven't always been perfect. I don't know how well the Athlon64 works, in this regard (as the memory controller is integrated in the processor). In summary: 1) ECC must be enabled, for scrubbing to work. 2) ECC robs performance, when an architecture supports byte or half word write, by requiring the use of read-modify-write cycles. The added delay for ECC calculations is normally hidden by the deep pipelines in modern processors. I don't know how this affects Athlon64. 3) Scrubbing removes single errors from memory words autonomously. Correctable or uncorrectable but detectable errors can be counted, or each one can cause an interrupt and be reported immediately to the OS. 4) Scrubbing should be opportunistic, and only do cycles when the CPU is not using the memory. But, there are bound to be situations, where the access latency for the processor is being increased, as the memory is currently finishing a scrubber induced memory cycle. An application benchmark, like Super_PI, may help you determine how good the implementation of the feature happens to be. (Run Super_PI with and without scrubbing, to see how much interference there is between scrubbing and normal CPU access.) 5) I have no idea which OSes support ECC and/or scrubbing. A server OS is more likely to do a good job at this, than a desktop OS. Unless you are running a server, I would leave it disabled. HTH, Paul |
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