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http://www.realworldtech.com/inc ... 2719&mode=print
原文请访问RWT
一些原先没有披露的细节：
1. L2 latency 低于12Cycle，L3在30-40 cycle之间
2. L3的设计："The advantage of an inclusive cache is that it can handle almost all coherency traffic without disturbing the private caches for each individual-core. If a cache access misses in the L3, it cannot be present in any of the L2 or L1 caches of the cores. On the other hand, Nehalem’s L3 also acts like a snoop filter for cache hits. Each cache line in the L3 contains four “core valid” bits denoting which cores may have a copy of that line in their private caches. If a “core valid” bit is set to 0, then that core cannot possibly have a copy of the cache line – while a “core valid” bit set to 1 indicates it is possible (but not guaranteed) that the core in question could have a private copy of the line. Since Nehalem uses the MESIF cache coherency protocol, as discussed previously, if two cores have valid bits, then the cache line is guaranteed to be clean (i.e. not modified). The combination of these two techniques lets the L3 cache insulate each of the cores from as much coherency traffic as possible, leaving more bandwidth available for actual data in the caches. "
性能的预期：
整数性能增长一般，HPC和浮点密集型程序将增长惊人，2倍或者更多都是有可能的（嘿嘿）。而企业级商业应用性能介于两者之间，不过，8核心的Beckton一年之后就会到来
In workloads that are not particularly bandwidth dependent, such as general integer applications, Nehalem will provide a moderate boost over the previous generation. The performance gains will largely come from the integrated memory controller, microarchitectural innovation and circuit techniques (the latter was not discussed by Intel at IDF and will probably be saved for later disclosure). For floating point and HPC workloads that are typically bandwidth bound, Nehalem will be nothing short of a miracle – with performance gains of 2X or better. Commercial server workloads such as OLTP databases, decision support and virtualization will certainly benefit from more bandwidth and lower latency as well, but not to the same extent as HPC or floating point applications. Of course, when thinking about performance it is essential to also keep time in mind – Beckton will be about a year behind Gainestown and Bloomfield.
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发表于 2008-4-4 17:12
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