Storage Efficient Hardware Prefetching using Delta Correlating - PowerPoint PPT Presentation

Storage Efficient Hardware Prefetching using Delta Correlating Prediction Tables Marius Grannæs Magnus Jahre Lasse Natvig Feb 14th 2008 www.ntnu.no M. Grannæs et.al., Storage Efficient Hardware Prefetching using Delta Correlating Prediction Tables

2 Delta Correlating Prefetch Tables — Perez et al. did a comparative survey of hardware prefetchers in 2004. • Reference Prediction Tables and PC/DC using a Global History Buffer — Delta Correlating Prediction Tables combines these two approaches and adds extra control for avoiding duplicate prefetching. — Perez et al. also found that you can make anything look good provided the right benchmarks and parameters. www.ntnu.no M. Grannæs et.al., Storage Efficient Hardware Prefetching using Delta Correlating Prediction Tables

3 Prefetcher Overview Sequential RPT PC/DC DCPT www.ntnu.no M. Grannæs et.al., Storage Efficient Hardware Prefetching using Delta Correlating Prediction Tables

3 Prefetcher Overview Sequential RPT PC/DC DCPT Sequential www.ntnu.no M. Grannæs et.al., Storage Efficient Hardware Prefetching using Delta Correlating Prediction Tables

3 Prefetcher Overview Sequential RPT PC/DC DCPT Sequential Constant Stride www.ntnu.no M. Grannæs et.al., Storage Efficient Hardware Prefetching using Delta Correlating Prediction Tables

3 Prefetcher Overview Sequential RPT PC/DC DCPT Sequential Constant Stride Repeating Pattern www.ntnu.no M. Grannæs et.al., Storage Efficient Hardware Prefetching using Delta Correlating Prediction Tables

3 Prefetcher Overview Sequential RPT PC/DC DCPT Sequential Constant Stride Repeating Pattern Complexity www.ntnu.no M. Grannæs et.al., Storage Efficient Hardware Prefetching using Delta Correlating Prediction Tables

3 Prefetcher Overview Sequential RPT PC/DC DCPT Sequential Constant Stride Repeating Pattern Complexity Delay www.ntnu.no M. Grannæs et.al., Storage Efficient Hardware Prefetching using Delta Correlating Prediction Tables

3 Prefetcher Overview Sequential RPT PC/DC DCPT Sequential Constant Stride Repeating Pattern Complexity Delay Storage Efficiency www.ntnu.no M. Grannæs et.al., Storage Efficient Hardware Prefetching using Delta Correlating Prediction Tables

4 Outline Motivation Reference Prediction Tables Properties of RPT prefetching PC/DC Prefetching Global History Buffer Delta Correlation Properties of PC/DC prefetching Delta Correlating Prefetch Tables DCPT Properties Results Concluding Remarks www.ntnu.no M. Grannæs et.al., Storage Efficient Hardware Prefetching using Delta Correlating Prediction Tables

5 Reference Prediction Tables Cache Miss: Last Addr. Delta State PC Training Initial Prefetch www.ntnu.no M. Grannæs et.al., Storage Efficient Hardware Prefetching using Delta Correlating Prediction Tables

6 Reference Prediction Tables Cache Miss: 1 Last Addr. Delta State PC Training Initial Prefetch www.ntnu.no M. Grannæs et.al., Storage Efficient Hardware Prefetching using Delta Correlating Prediction Tables

7 Reference Prediction Tables Cache Miss: 1 -- 100 1 Init Last Addr. Delta State PC Training Initial Prefetch www.ntnu.no M. Grannæs et.al., Storage Efficient Hardware Prefetching using Delta Correlating Prediction Tables

8 Reference Prediction Tables Cache Miss: 1 3 3 2 100 Train 1 -- Last Addr. Delta State PC Training Initial Prefetch www.ntnu.no M. Grannæs et.al., Storage Efficient Hardware Prefetching using Delta Correlating Prediction Tables

9 Reference Prediction Tables Cache Miss: 1 3 5 5 2 100 Prefetch 3 2 Last Addr. Delta State PC Training Initial Prefetch www.ntnu.no M. Grannæs et.al., Storage Efficient Hardware Prefetching using Delta Correlating Prediction Tables

10 Properties of RPT prefetching — Very high accuracy — Relatively low cost - Table lookup, comparator and subtraction — Small memory footprint — Only able to capture constant strides www.ntnu.no M. Grannæs et.al., Storage Efficient Hardware Prefetching using Delta Correlating Prediction Tables

11 Global History Buffer Index Table Global History Buffer Address Ptr PC Ptr 100 3 Delta Buffer 1 www.ntnu.no M. Grannæs et.al., Storage Efficient Hardware Prefetching using Delta Correlating Prediction Tables

12 Global History Buffer Index Table Global History Buffer Address Ptr PC Ptr 100 5 3 Delta Buffer 1 www.ntnu.no M. Grannæs et.al., Storage Efficient Hardware Prefetching using Delta Correlating Prediction Tables

13 Global History Buffer Index Table Global History Buffer Address Ptr PC Ptr 100 5 3 Delta Buffer 1 www.ntnu.no M. Grannæs et.al., Storage Efficient Hardware Prefetching using Delta Correlating Prediction Tables

14 Global History Buffer Index Table Global History Buffer Address Ptr PC Ptr 100 5 3 Delta Buffer 1 www.ntnu.no M. Grannæs et.al., Storage Efficient Hardware Prefetching using Delta Correlating Prediction Tables

15 Global History Buffer Index Table Global History Buffer Address Ptr PC Ptr 100 5 3 Delta Buffer 1 www.ntnu.no M. Grannæs et.al., Storage Efficient Hardware Prefetching using Delta Correlating Prediction Tables

16 Global History Buffer Index Table Global History Buffer Address Ptr PC Ptr 100 5 3 Delta Buffer 1 www.ntnu.no M. Grannæs et.al., Storage Efficient Hardware Prefetching using Delta Correlating Prediction Tables

17 Global History Buffer Index Table Global History Buffer Address Ptr PC Ptr 100 5 3 Delta Buffer 2 1 www.ntnu.no M. Grannæs et.al., Storage Efficient Hardware Prefetching using Delta Correlating Prediction Tables

18 Global History Buffer Index Table Global History Buffer Address Ptr PC Ptr 100 5 3 Delta Buffer 2 2 1 www.ntnu.no M. Grannæs et.al., Storage Efficient Hardware Prefetching using Delta Correlating Prediction Tables

19 Delta Correlation 10 11 13 16 17 19 22 24 25 1 2 3 1 2 3 1 2 www.ntnu.no M. Grannæs et.al., Storage Efficient Hardware Prefetching using Delta Correlating Prediction Tables

20 Delta Correlation 10 11 13 16 17 19 22 24 25 1 2 3 1 2 3 1 2 www.ntnu.no M. Grannæs et.al., Storage Efficient Hardware Prefetching using Delta Correlating Prediction Tables

21 Delta Correlation 10 11 13 17 18 20 23 24 25 1 2 3 1 2 3 1 2 www.ntnu.no M. Grannæs et.al., Storage Efficient Hardware Prefetching using Delta Correlating Prediction Tables

22 Delta Correlation 10 11 13 17 18 20 23 24 25 1 2 3 1 2 3 1 2 www.ntnu.no M. Grannæs et.al., Storage Efficient Hardware Prefetching using Delta Correlating Prediction Tables

23 Delta Correlation 10 11 13 17 18 20 23 24 25 1 2 3 1 2 3 1 2 www.ntnu.no M. Grannæs et.al., Storage Efficient Hardware Prefetching using Delta Correlating Prediction Tables

24 Delta Correlation 10 11 13 17 18 20 23 24 25 1 2 3 1 2 3 1 2 www.ntnu.no M. Grannæs et.al., Storage Efficient Hardware Prefetching using Delta Correlating Prediction Tables

25 Delta Correlation 10 11 13 16 17 19 22 24 25 1 2 3 1 2 3 1 2 www.ntnu.no M. Grannæs et.al., Storage Efficient Hardware Prefetching using Delta Correlating Prediction Tables

26 Delta Correlation 10 11 13 16 17 19 22 23 25 1 2 3 1 2 3 1 2 www.ntnu.no M. Grannæs et.al., Storage Efficient Hardware Prefetching using Delta Correlating Prediction Tables

27 Delta Correlation 10 11 13 16 17 19 22 23 25 1 2 3 1 2 3 1 2 www.ntnu.no M. Grannæs et.al., Storage Efficient Hardware Prefetching using Delta Correlating Prediction Tables

28 Properties of PC/DC prefetching — Can capture a very wide range of patterns — High accuracy and performance — The global history must be very large to capture relevant data — Pointer chasing — The deltas are recalucated every time — The number of deltas can vary www.ntnu.no M. Grannæs et.al., Storage Efficient Hardware Prefetching using Delta Correlating Prediction Tables

29 Delta Correlating Prefetch Tables PC Last Addr. Last Pref. D D D D D D Ptr www.ntnu.no M. Grannæs et.al., Storage Efficient Hardware Prefetching using Delta Correlating Prediction Tables

30 Delta Correlating Prefetch Tables 10 100 10 - - - - - - - - PC Last Addr. Last Pref. D D D D D D Ptr www.ntnu.no M. Grannæs et.al., Storage Efficient Hardware Prefetching using Delta Correlating Prediction Tables

31 Delta Correlating Prefetch Tables 10 11 100 10 - - - - - - - - PC Last Addr. Last Pref. D D D D D D Ptr www.ntnu.no M. Grannæs et.al., Storage Efficient Hardware Prefetching using Delta Correlating Prediction Tables

32 Delta Correlating Prefetch Tables 10 11 100 10 - 1 - - - - - - PC Last Addr. Last Pref. D D D D D D Ptr www.ntnu.no M. Grannæs et.al., Storage Efficient Hardware Prefetching using Delta Correlating Prediction Tables