Vincent, Your statement only holds true for the cache bandwidth (which somewhat scales with the core frequency), not the DDR3 memory controller bandwidth (or latency for that matter). The main limiting factor for the DDR3 memory bandwidth is the # of channels (i.e now much data you can get in parallel) and how fast the dram is (i.e frequency the DDR3 interface runs on).
cheers, --Steffen On 9/14/2012 17:08, Vincent Diepeveen wrote: > Yes, > > You can easily see this in the latency numbers of higher clocked > processors. they're faster > than lower clocked i7's of the same kind. > > Let me email directly to you a test i wrote for that some years ago. > > > > > > On Sep 14, 2012, at 5:04 PM, Orion Poplawski wrote: > >> On 09/14/2012 08:54 AM, Vincent Diepeveen wrote: >>> The memory controller is on die, so the bandwidth that the CPU >>> itself delivers, >>> independant from the number of channels, is dependant upon the CPU >>> frequency. >>> >>> Higher frequency means more bandwidth simply with the given memory >>> channels >>> available. >>> >> >> Really? >> >> http://ark.intel.com/compare/64590,64591,64587 >> >> Clock Speed 2 GHz 2.5 GHz 3.3 GHz >> Max Turbo Frequency 2.8 GHz 3 GHz 3.5 GHz >> # of Memory Channels 4 4 4 >> Max Memory Bandwidth 51.2 GB/s 42.6 GB/s 51.2 GB/s >> >>> >>> On Sep 14, 2012, at 4:41 PM, Orion Poplawski wrote: >>> >>>> On 09/14/2012 05:00 AM, Igor Kozin wrote: >>>>> if memory bandwidth is your concern then there are models which >>>>> boost >>>>> it quite significantly. e.g. >>>>> http://ark.intel.com/products/64584/Intel-Xeon-Processor- >>>>> E5-2660-20M-Cache-2_20-GHz-8_00-GTs-Intel-QPI >>>>> >>>>> probably very few codes are going to benefit from AVX without extra >>>>> efforts but BW is a clear win. >>>>> i'm seeing a good speed up on some applications which can be >>>>> attributed to higher BW. >>>> >>>> There are 6.4, 7.2, and 8 GT/s chips >>>> >>>> This is an interesting puzzle and the mid tier price point: >>>> >>>> DUAL INTEL XEON 6C E5-2640 (2.5GHz/7.2GT/s/15MB) CPU [+ $1,810.00] >>>> DUAL INTEL XEON 4C E5-2643 (3.3GHz/8GT/s/10MB) CPU [+ $1,798.00] >>>> DUAL INTEL XEON 8C E5-2650 (2GHz/8GT/s/20MB) CPU [+ $2,270.00] >>>> >>>> So for BW limited one would go with the second two, but you have >>>> a big choice >>>> between low cores/cache high MHz and high cores/cache low MHz. >>>> >>>> -- >>>> Orion Poplawski >>>> Technical Manager 303-415-9701 x222 >>>> NWRA, Boulder Office FAX: 303-415-9702 >>>> 3380 Mitchell Lane or...@nwra.com >>>> Boulder, CO 80301 http://www.nwra.com >>>> _______________________________________________ >>>> Beowulf mailing list, Beowulf@beowulf.org sponsored by Penguin >>>> Computing >>>> To change your subscription (digest mode or unsubscribe) visit >>>> http://www.beowulf.org/mailman/listinfo/beowulf >> >> >> -- >> Orion Poplawski >> Technical Manager 303-415-9701 x222 >> NWRA, Boulder Office FAX: 303-415-9702 >> 3380 Mitchell Lane or...@nwra.com >> Boulder, CO 80301 http://www.nwra.com > > _______________________________________________ > Beowulf mailing list, Beowulf@beowulf.org sponsored by Penguin Computing > To change your subscription (digest mode or unsubscribe) visit > http://www.beowulf.org/mailman/listinfo/beowulf > -- Steffen Persvold, Chief Architect NumaChip Numascale AS - www.numascale.com Tel: +47 92 49 25 54 Skype: spersvold _______________________________________________ Beowulf mailing list, Beowulf@beowulf.org sponsored by Penguin Computing To change your subscription (digest mode or unsubscribe) visit http://www.beowulf.org/mailman/listinfo/beowulf
