Quality and Performance Advantages of DDR4 over DDR3 Bacchus... · • CAS latency increases with...

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Agenda

1.Comparison of DDR3 and DDR4 2.DDR4 Memory Throughput and Latency 3.A tale of two 8GB DDR4 DIMMs

Results of micro benchmark not affiliated with any

specific application

DIMM Labels 16GB 2Rx4 PC4 2133 P R Capacity Ranks &

Width DDR4 Gen DDR4 Bit Rate DDR4 CAS Latency DDR4 DIMM Type

4 GB 8 GB 16 GB 32 GB 64 GB

1Rx8 2Rx8 1Rx4 2Rx4 4Rx4

PC4 = 1.2V 2666 MT/s 2400 MT/s 2133 MT/s

S = 19 or 14.25 ns R = 17 or 14.17 ns P = 15 or 14.06 ns

E = UDIMM R = RDIMM L = LRDIMM

16GB 2Rx4 PC3 14900 R 13 Capacity Ranks &

Width DDR3 Gen and

Voltage DDR3 DIMM Data

Rate DDR3 DIMM Type DDR3 CAS Latency

4 GB 8 GB 16 GB 32 GB 64 GB

1Rx8 2Rx8 1Rx4 2Rx4 4Rx4

PC3 = 1.5V PC3L = 1.35V

14900 => 1866 12800 => 1600 10600 => 1333

E = UDIMM R = RDIMM L = LRDIMM

13 = 13.93 ns at 1866 11 = 13.75 ns at 1600 9 = 13.50 ns at 1333

ProLiant 2-Socket DDR3 and DDR4 NUMA Architecture

CPU 1

SNB/IVB HSW

CPU 2

SNB/IVB HSW

Ch3 Ch4 Ch2 Ch1

24 DIMM Design (3 Slots per Channel (3SPC))

CPU 1

SNB/IVB HSW

16 DIMM Design (2SPC)

CPU 2

SNB/IVB HSW

Ch3 Ch4 Ch2 Ch1

Ch3 Ch4 Ch2 Ch1

Ch3 Ch4 Ch2 Ch1

Memory Bus

Populate white slots

first

QPI Bus

DDR4 and DDR3 Data Rates

Generation Operating Voltage

1DPC

2DPC

3DPC

DDR4 1.20 V 2133 2133* 1866* DDR3 1.35 V 1600 1600* 1066* DDR3 1.50 V 1866 1866* 1333*

* HP Smart Memory required DPC = DIMM per Channel

DDR4 and DDR3 Idle Latency

DDR4 1-rank DIMMs have lower latency than 2-rank DIMMs

DDR3 measured on ProLiant DL360 Gen8


DDR4 RDIMM relative to DDR3 16GB 2Rx4 RDIMM at 1 DIMM per Channel (DPC)

DDR4 offers higher throughput at lower power and latency than DDR3



Resilience

• DDR4 provides retry on Address Parity and Uncorrectable Errors –More immune to transient errors – Previously caused a system shutdown – Longer Mean Time Between Failures

• DDR3 causes a system shutdown with Address Parity or UC Errors

DDR4 is more resilient than DDR3

Agenda




Factors that affect Throughput and Latency

1.Number of populated channels 2.Number of active cores 3.Data rate and CAS latency 4.Percentage of write traffic 5.Number of ranks on the channel

Load-to-use Idle Latency and CAS Latency

• CAS latency increases with increasing Data Rate • Idle latency decreases with increasing Data Rate

• Because the internal memory controller clock is the same as the Data Rate • Same latencies with HW pre-fetcher disabled

CA

S L

aten

cy (n

s)

CL15 CL13

CL11

CL9

Remote snoop latency == Local memory latency

Measured on ProLiant DL360 Gen9

Factors affecting Throughput

Writes


Impact of Throughput on Latency

Stair step is due to cores on alternating sockets


Impact of Throughput on Power

0.00.51.01.52.02.53.03.54.04.55.0

0 25 50 75 100 125

DIM

M P

ower

(W)

Throughput (GB/s)

DL360 Gen9 2-Socket Server with 8x 16GB 2Rx4 RDIMM 1DPC

DDR4-2133DDR4-1866DDR4-1600

• Power consumption is dominated by throughput - not Data Rate – Stair step is due to cores on alternating sockets


Agenda




8GB 1Rx4 relative to 2Rx8 RDIMM Same number of DRAMs

1Rx4 • Lower Latency • X4 ECC Protection

2Rx8 • More Throughput • Lower Power • Less ECC Protection


Wrap-up

1.Comparison of DDR3 and DDR4 – DDR4 has superior throughput, latency, power

and resiliency 2.DDR4 Memory Throughput and Latency

– Affected by occupied channels, DPC, data rates, ranks per channel, active cores, writes

3.A tale of two 8GB DDR4 DIMMs – Single-rank has better latency and ECC

protection than dual-rank

The End – Many Thanks!

Quality and Performance Advantages of DDR4 over DDR3 Bacchus... · • CAS latency increases with...

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