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What's CPU prefetching?

post #1 of 11
Thread Starter 
I am wondering what is CPU prefetching and if I should have it enabled?
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post #2 of 11
I know what prefetch in Windows is but I don't know if CPU prefetching is related...

(Off topic, consider removing 1 DIMM for 2 DIMMs/dual channel operation, or adding 1 more DIMM.... should speed everything up instantly)
post #3 of 11
Thread Starter 
I was running a 8gs but my CPU cooler was to big and the heat spreaders on my memory made it impossible to put the fourth one back. Why would removing make it faster? And having 4gs would be better or does it matter?
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post #4 of 11
Dual channel. 2 or 4 DIMMs = proper dual channel = doubled bandwidth = increases in just about everything
Seems like a tough constraint there with that cooler, considering you're running an x3 would a downgrade or moving the fans around (i.e. push, pull...) be out of the option? 8GB will benefit you in both dual channel and RAM amount. You could try putting the RAM in BEFORE remounting the cooler (I have to do that but my ECOs fit)
post #5 of 11
Because at the moment you're running in Single Channel RAM mode. However if you look at Wikipedia (yeah I know.....) the performance gains are minimal as reported by Tomshardware and laptoplogic. Don't quote me on this but I believe that the reason why Intel has made the SB chips dual channel instead of continuing to run with the latest/greatest triple channel technology.
Quote:
There have been varying reports as to the performance increase of dual-channel configurations, with some tests citing significant performance gains while others suggest almost no gain.

Tom's Hardware found little significant difference between single-channel and dual-channel configurations in synthetic and gaming benchmarks (using a "modern" system setup). In its tests, dual channel gave at best a 5% speed increase in memory-intensive tasks.[3] Another comparison by laptoplogic.com resulted in a similar conclusion for integrated graphics.[4] The test results published by Tom's Hardware had a discrete graphics comparison.

The difference can be far more significant in applications that manipulate large amounts of data in memory. A comparison by TechConnect Magazine demonstrated considerable gains for dual-channel in tasks using block sizes greater than 4 MB, and during stream processing by the CPU.[5][dead link]

Source: http://en.wikipedia.org/wiki/Dual-channel_architecture#Performance
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post #6 of 11
Thread Starter 
Quote:
Originally Posted by xd_1771;12454037 
Dual channel. 2 or 4 DIMMs = proper dual channel = doubled bandwidth = increases in just about everything
Seems like a tough constraint there with that cooler, considering you're running an x3 would a downgrade or moving the fans around (i.e. push, pull...) be out of the option? 8GB will benefit you in both dual channel and RAM amount. You could try putting the RAM in BEFORE remounting the cooler (I have to do that but my ECOs fit)

I was considering buying a smaller heat spreader for the 4th stick. I tried putting it in with the existing one on it but as long as it has not heat spreader on it will fit.
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post #7 of 11
So heatspreader will not fit no matter what even if RAM first, then cooler... hm. I'd be wary about taking off memory heatspreader, taking off a heatspreader is pretty risky business, many people detach the ICs from the PCB of the memory doing so.
post #8 of 11
http://portal.acm.org/citation.cfm?id=279529

Prefetching into CPU caches has long been known to be effective in reducing the cache miss ratio, but known implementations of prefetching have been unsuccessful in improving CPU performance. The reasons for this are that prefetches interfere with normal cache operations by making cache address and data ports busy, the memory bus busy, the memory banks busy, and by not necessarily being complete by the time that the prefetched data is actually referenced. In this paper, we present extensive quantitative results of a detailed cycle-by-cycle trace-driven simulation of a uniprocessor memory system in which we vary most of the relevant parameters in order to determine when and if hardware prefetching is useful. We find that, in order for prefetching to actually improve performance, the address array needs to be double ported and the data array needs to either be double ported or fully buffered. It is also very helpful for the bus to be very wide (e.g., 16 bytes) for bus transactions to be split and for main memory to be interleaved. Under the best circumstances, i.e., with a significant investment in extra hardware, prefetching can significantly improve performance. For implementations without adequate hardware, prefetching often decreases performance.
 
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post #9 of 11
Quote:
Originally Posted by Lord Xeb;12454422 
http://portal.acm.org/citation.cfm?id=279529

Prefetching into CPU caches has long been known to be effective in reducing the cache miss ratio, but known implementations of prefetching have been unsuccessful in improving CPU performance. The reasons for this are that prefetches interfere with normal cache operations by making cache address and data ports busy, the memory bus busy, the memory banks busy, and by not necessarily being complete by the time that the prefetched data is actually referenced. In this paper, we present extensive quantitative results of a detailed cycle-by-cycle trace-driven simulation of a uniprocessor memory system in which we vary most of the relevant parameters in order to determine when and if hardware prefetching is useful. We find that, in order for prefetching to actually improve performance, the address array needs to be double ported and the data array needs to either be double ported or fully buffered. It is also very helpful for the bus to be very wide (e.g., 16 bytes) for bus transactions to be split and for main memory to be interleaved. Under the best circumstances, i.e., with a significant investment in extra hardware, prefetching can significantly improve performance. For implementations without adequate hardware, prefetching often decreases performance.

so what i get from this post is... lets say I have a i7 950 and all I do is schoolwork/web/youtube/multitask with web page-videos-games etc/ or high end games does this mean Id be better off just disabling it for my usage conditions whether its oc'd or not?

and by what being the inadequate hardware per say? gpu/ram/hdd?
Edited by Amann - 2/20/11 at 4:38am
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post #10 of 11
Quote:
Originally Posted by NeoVincent;12453796 
I was running a 8gs but my CPU cooler was to big and the heat spreaders on my memory made it impossible to put the fourth one back. Why would removing make it faster? And having 4gs would be better or does it matter?

Buy new ram. Those tall heatsinks are pure marketing anyway. I ditched my underperforming Corsair sticks and got some Crucial Ballistix Tracers for that very reason. Now my CPU heatsink is in the right way and my ram performs much better.

I don't think that I would enable CPU Prefetching. Don't think that in the end it would have any advantage.
Edited by coonmanx - 2/20/11 at 7:32am
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