Tag Archives: latency

Inphi reports Q2 2012 results

LRDIMM sales occur – and benchmarks

Inphi reported Q2 2012 results.

Inphi suggests sales of both 16GB LRDIMMs and 32GB LRDIMMs.

It is likely that most of these may be 32GB LRDIMMs, since 16GB LRDIMMs are non-viable vs. RDIMMs.

Inphi is shy about reporting benchmarks for LRDIMMs – saying they will be available second half of 2012.

Benchmarks for LRDIMMs should have been available prior to LRDIMM launch.

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Latency and throughput figures for LRDIMMs emerge

LRDIMMs exhibit 45% worse latency and 36.7% worse throughput at 3 DPC

LRDIMMs (which are a new standard and incompatible with DDR3 RDIMMs) exhibit significant performance impairment at 3 DPC compared to RDIMM-compatible HCDIMMs:

– LRDIMMs have 45% worse latency than HCDIMMs (235ns vs. 161.9ns for HCDIMMs)
– LRDIMMs have 36.7% worse throughput than HCDIMMs (40.4GB/s vs. 63.9GB/s for HCDIMMs)

And this is when HCDIMMs are run at a SLOWED down 1066MHz at 3 DPC (in order to match the lower max achievable speed of the LRDIMMs).

This comparison – at SAME speed – highlights the architectural weaknesses of the LRDIMM design irrespective of the speeds.

When compared at the MAXIMUM achievable speeds (LRDIMMs at 1066MHz at 3 DPC and HCDIMM at 1333MHz at 3 DPC):

– LRDIMMs have approx. 45% worse latency than HCDIMMs (235ns vs. 161.9ns for HCDIMMs)
– LRDIMMs have 40% worse throughput than HCDIMMs (40.4GB/s vs. 68.1GB/s for HCDIMMs)

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Memory choices for Cisco UCS B200 M3 Blade Server (Romley)

This server has 24 DIMM slots for a total of 384GB (using 16GB RDIMMs).

However I cannot find any docs outlining the speeds achievable at 1 DPC, 2 DPC, 3 DPC (as are available from IBM and others).

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LRDIMM latency vs. DDR4

UPDATE: 06/24/2012: Invensas on LRDIMM design inferiority vs. HyperCloud
UPDATE: 07/27/2012 – confirmed HCDIMM similar latency as RDIMMs
UPDATE: 07/27/2012 – confirmed LRDIMM latency and throughput weakness

RDIMMs have a 1 cycle latency compared to UDIMMs (unregistered DIMMs).

LRDIMMs have a “5 ns latency penalty” compared to RDIMMs (from Inphi LRDIMM blog).

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