Memory Subsystem: Latency

To measure latency, we use the open source TinyMemBench benchmark. The source was compiled for x86 with gcc 4.8.2 and optimization was set to "-O2". The measurement is described well by the manual of TinyMemBench:

Average time is measured for random memory accesses in the buffers of different sizes. The larger the buffer, the more significant the relative contributions of TLB, L1/L2 cache misses, and DRAM accesses become. All the numbers represent extra time, which needs to be added to L1 cache latency (4 cycles).

We tested with dual random read, as we wanted to see how the memory system coped with multiple read requests. To keep the graph readeable we limited ourselves to the CPUs that were different. The Xeon E5-2695 and 2699 have a very similar memory subsytem (dual memory controller) so we tested only the E5-2699.

The massive L3 caches do have some disadvantages: latency goes up. The L3 cache of the Xeon E5-2699 v3 (45MB) has a latency between 20 and 32 ns while the 20MB cache of the Xeon E5-2690 hovers between 15 and 20 ns. That translates to about 90 cycles versus 60, which is considerable. However, it's not a case of the Haswell's L3 cache being a lot worse: the 20MB L3 cache of the Xeon E5-2667 v3 is only slightly slower than the Xeon E5-2690 and is still faster than the Xeon E5-2697 v2 (30MB). The main culprit is simply dealing with a huge amount of cache on the E5-2699 v3. In the next test, we will focus on the latency of the DRAM subsystem.

Dual Random read Latency

The DRAM subsystem is still three or four times slower than the massive L3 cache. LRDIMMs still have a very small latency overhead – +3.6% at the most – but that is neglible.

DDR4-2133 seems to have the same latency as DDR3-1866 . We measured 81.6 ns on the Xeon E5-2697 v2. Considering that DDR4-2400 is just around the corner, DDR4 will quickly give a performance boost to the new platform.

Memory Subsystem: Bandwidth Single-Threaded Integer Performance
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  • coburn_c - Monday, September 08, 2014 - link

    MY God - It's full of transistors! Reply
  • Samus - Monday, September 08, 2014 - link

    I wish there were socket 1150 Xeon's in this class. If I could replace my quad core with an Octacore... Reply
  • wireframed - Saturday, September 20, 2014 - link

    If you can afford an 8-core CPU, I'm sure you can afford a S2011 board - it's like 15% of the price of the CPU, so the cost relative to the rest of the platform is negligible. :)
    Also, s1150 is dual-channel only. With that many cores, you'll want more bandwidth.
    Reply
  • peevee - Wednesday, March 25, 2015 - link

    For many, if not most workloads it will be faster to run 4 fast (4GHz) cores on 4 fast memory channels (DDR4-2400+) than 8 slow (2-3GHz) cores on 2 memory channels. Of course, if your workload consists of a lot of trigonometry (sine/cosine etc), or thread worksets completely fit into 2nd level cache (only 256k!), you may benefit from 8/2 config. But if you have one of those, I am eager to hear what it is. Reply
  • tech6 - Monday, September 08, 2014 - link

    The 18 core SKU is great news for those trying to increase data center density. It should allow VM hosts with 512Gb+ of memory to operate efficiently even under demanding workloads. Given the new DDR4 memory bandwidth gains I wonder if the 18 core dual socket SKUs will make quad socket servers a niche product? Reply
  • Kevin G - Monday, September 08, 2014 - link

    In fairness, quad socket was already a niche market.

    That and there will be quad socket version of these chips: E5-4600v3's.
    Reply
  • wallysb01 - Monday, September 08, 2014 - link

    My lord. My thought is that this really shows that v3 isn’t the slouch many thought it would be. An added 2 cores over v2 in the same price range and turbo boosting that appears to functioning a little better, plus the clock for clock improvements and move to DDR4 make for a nice step up when all combined.

    I’m surprised Intel went with an 18 core monster, but holy S&%T, if they can squeeze it in and make it function, why not.
    Reply
  • Samus - Monday, September 08, 2014 - link

    I feel for AMD, this just shows how far ahead Intel is :\ Reply
  • Thermogenic - Monday, September 08, 2014 - link

    Intel isn't just ahead - they've already won. Reply
  • olderkid - Monday, September 08, 2014 - link

    AMD saw Intel behind them and they wondered how Intel fell so far back. But really Intel was just lapping them. Reply

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