Memory Performance and Scalability of Intel’s and AMD’s Dual-Core Processors: A Case Study

1. Memory Performance and Scalability of Intel’s and AMD’s Dual-Core Processors: A Case Study Lu Peng1, Jih-Kwon Peir2, Tribuvan K. Prakash1, Yen-Kuang Chen3 and David Koppelman1 1Louisiana State University 2University of Florida 3Intel Corporation

2. Motivation • Dual-Core processors are popular. • Understanding the impact of memory hierarchy to overall performance. • What are important factors for memory hierarchy performance? • How about speedups for dual threads? Peng, Louisiana State University

3. Selected Three Dual-Core Processors On-Chip Off-Chip Shared Intel Core 2 Duo Intel Pentium D AMD Athlon 64X2 • Shared Cache vs. Private Cache • On-chip vs. Off-chip Inter-core communication • On-chip vs. Off-chip memory controller Peng, Louisiana State University

4. Selected Three Dual-Core Processors Intel Core 2 Duo Intel Pentium D AMD Athlon 64X2 • Core 2 Duo: • Shared L2 cache, no L2 coherence, beneficial with one active core, • higher latency, fairness issue • When L1 miss, search L2 and the other L1 simultaneously, fast • cache-cache transfer and L1 coherence (like a bus) • Memory controller off-chip, aggressive memory dependence predict Peng, Louisiana State University

5. Selected Three Dual-Core Processors Intel Core 2 Duo Intel Pentium D AMD Athlon 64X2 • Pentium D: • Two Pentium 4 on a chip, use technology remap approach (SMP) • Private L2 cache, MESI coherence, require memory update for MS, • off-chip FSB for memory update, L1 coherence also go through FSB • Memory controller off-chip, longer delay but adaptive to new DRAM Peng, Louisiana State University

6. Selected Three Dual-Core Processors Intel Core 2 Duo Intel Pentium D AMD Athlon 64X2 • Athlon 64x2: • Private L2 cache, connected through HyperTransport • Use system request queue for internal commun. Between two cores • MOESI coherence protocol allows shared-modified block in O-state • no need for memory updated when read a remote Modified block Peng, Louisiana State University

7. Specifications of the selected processors Peng, Louisiana State University

8. Methodology • Same platform: SUSE Linux 10.1 with kernel 2.6.16-smp • Micro-benchmarks • Memory bandwidth and latency measured by Lmbench • A lockless program [19] measuring cache-to-cache latency • Real workloads • Single threaded: SPEC CPU2000 and CPU2006 • Multi-threaded: blastp, hmmpfam, SPECjbb2005 and SPLASH2 Peng, Louisiana State University

9. Memory operations from Lmbench • Memory read - measuring the time to read every 4 byte word from memory. • Memory write - measuring the time to write every 4 byte word to memory. • Other operations such as Memory bzero etc. Refer the paper for details. Peng, Louisiana State University

10. Lockless Program measuring cache-to-cache latency • Doesn’t employ expensive read-modify-write atomic primitives. • Maintains a lockless counter for each thread. • *pPong is in a different cache line with *pPing. • C2C latency for Core 2 Duo, Pentium D and Athlon 64X2: 33ns, 133ns and 68ns respectively. Peng, Louisiana State University

11. Memory bandwidth collected from the lmbench suite Private cache is faster! 3. Athlon 64X2 provides doubled memory read bandwidth for two copies lmbench, benefiting from its on-chip memory controller. 2. Pentium D shows the best memory read bandwidthwhen the array size is less than its L2 size. 1. In general, Core 2 Duo and Athlon 64 X2 have better bandwidth than that of Pentium D. Peng, Louisiana State University Doubled!!

12. SPEC CPU2000 and CPU2006 benchmarks’ execution time 4. When mixed with another program, CPU bounded program’s execution time increasing is small. 2. Athlon shows the best performance for ammp which has a large working set, resulting a high L2 miss rate. 3. When mixed with another program, memory intensive program’s execution time increasing is large. 1. Core 2 Duo processor runs fastest for almost all workloads, especially for art, mcf. Peng, Louisiana State University

13. Multi-programmed speedup of mixed SPEC CPU 2000/2006 benchmarks 2. CPU bounded program shows the best speedup. 3. Memory bounded program shows the worst speedup. 1. Athlon 64X2 achieves the best speedup for all workloads. Peng, Louisiana State University

14. Multithreaded Program Behaviors 2. Core 2 Duo shows the best speedup for ocean due to high cache-to-cache transfer ratio. Verified by Intel VTune Analyzer. 1. Core 2 Duo’s single thread performance boosts because of larger L2 cache. 3. Pentium D shows the best speedup for barnes because of the low cache miss rate Peng, Louisiana State University

15. Conclusions • Analyzed the memory hierarchy of selected Intel and AMD dual-core processors. • For the best performance and scalability, the following are important factors: • fast cache-to-cache communication; • large L2 or shared capacity; • fast front side bus; • on-chip memory controller. • fair resource (cache) sharing. Peng, Louisiana State University

16. Thank you! Questions? Peng, Louisiana State University

17. Backup Slides (Memory load latency collected from the lmbench suite) Peng, Louisiana State University

18. Memory latency collected from the lmbench suite (continued) • Latencies for all configurations jump after the array size is larger than L2 sizes. • When the stride size is equal to 128 bytes, Pentium D still benefits partially but the L2 prefetchers of Core 2 Duo and Athlon 64X2 is not triggered. • When the stride size is large than 128 bytes, Athlon 64X2’s on-die memory controller and separate I/O HyperTransport show the advantage. • Two copies of lmbench suites bring more pressures on Pentium D. Peng, Louisiana State University

19. Backup Slides (Bandwidth for STREAM / STREAM2) • The add operation is a loop of c[i] = a[i] + b[i], which can easily take advantage of the SSE2 packet operations. It shows higher bandwidth. • Intel Core 2 Duo shows the best bandwidth for all operations because of L1 data prefetchers and the faster Front Side Bus. • Athlon 64X2 has better bandwidth than that of Pentium D due to its faster on-chip memory controller. Peng, Louisiana State University