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rick merritt
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Not your father's PCIe
rick merritt   2/25/2014 5:32:10 PM
Can a non-stadard PCIe system interconnect gain much traction?

interconnect Guy
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Re: Not your father's PCIe
interconnect Guy   2/26/2014 5:58:32 AM
sadly RIO or RapidIO is several signaling generations behind, at 10GB/sec  While others are at 27Gb/Sec  (per pair)  and RapidIO switches are single sourced at IDT.

interconnect Guy
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Re: Not your father's PCIe
interconnect Guy   2/26/2014 7:54:53 AM

Per the RapidIO website:

"The 10xN specification, backward compatible with RapidIO Gen1 and Gen2 systems, supports 10.3125 Gbaud per serial lane"

The 25GB story is:

"RapidIO specifications are under development to support 25...."

Other interconnects are shipping 25Gbaud Now, and yes IP has been available for years, but never full cores for RapidIO (just thin Phy layers) complete cores are available for FPGA's for interconnects like PCIe and Ethernet.

You may have access to information about roadmaps for Gen 3 RapidIO parts, but the the reality is Infiniband, PCIe and Ethernet are shipping these speeds, and have been for sometime in volume.

In Niche applications the second sourcing may not be a issue, but in volume it is.

Freescale and TI support both PCIe and Ethernet. (and older sRIO) (Gen2)

Per the RapidIO Product showcase last Freescale product for sRIO was 2008

rick merritt
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Re: Not your father's PCIe
rick merritt   2/26/2014 10:44:35 AM
@GSMD: Thanks for sharing your expertise.

As I underdstand it, A3Cube is claiming advances in latency, not necessarily throughput. Their goal is to enable a single system image over a variant of PCIe.

What do you think about their latency claims?

rick merritt
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Re: Not your father's PCIe
rick merritt   2/26/2014 11:09:53 PM
@GSMD: So A3Cube's latency of 100 nanoseconds is the same as SRIO--so why do they bother? Game over for them?

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ANON1245102408113   2/27/2014 4:30:47 PM
GSMD, We would love a chance to talk with you to go over all of this and dive deeper into the technology so you have the right understanding of what it is. Where can we contact you?

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Re: Not your father's PCIe
antoanto   2/27/2014 4:41:11 PM
Who wrote the article wrong the latency number, we have a memory to memory latency of about 750 nanoseconds ( including software latency).

The goal of the system is to use the memory mapping capability of the PCIe to the fabric to avoid any protocol encapsulation ( like Eth) to maintain the lower latency is possible and working bypassing the operating system kernel stack.

In x86 server there is no RIO native interface so also Rapid IO bridge must plug into a PCIe slot, also for the IB so in x86 server the minimum latency that you can experience it the rout complex latency.
That is the reason because we extend the memory mapping of the PCIe.

RONNIEE Express is a low latency interconnection or data plane that use shared memory mapping for the communication between nodes extending the memory mapping used by the PCIe.

RONNIEE Express implement the support for a low latency 3D torus topology with flow control and traffic congestion management.

The most interesting thing of this interconnection is that permit to implement a TCP socket in memory that use the memory mapping for the communication bypassing the kernel and permit to use unmodified TCP application with a 1-2 microseconds latency with no modification.

This latency of our memory mapped socket is 10 time less that RapidIO RIONET so our memory approach is something that is really really powerful and it is not limited to the PCIe, but opens a new way to use distributed memory for communication


To understand better watch this video http://www.youtube.com/watch?v=YIGKks78Cq8


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Re: Not your father's PCIe
PCIeFabricNow   2/27/2014 4:43:19 PM
The discussion in this thread seems to have migrated off topic, since the original question pertained to the viability of a PCIe fabric.  But since this has turned into a discussion of the merits of SRIO, it makes sense to compare PCIe and SRIO for use as a general-purpose fabric.  And that comparison comes out significantly in favor of PCIe.

For purposes of full disclosure here, I am an advocate of using PCIe as a rack-level fabric, and a PLX employee.

The major advantage of PCIe as a fabric is that almost every device -- CPUs, NICs, HBAs, HCAs, FPGAs, you name it -- has a PCIe port as at least one of its connection points, meaning you can eliminate all of the bridging devices necessary in other fabric types.  This reduces power and cost, since you are eliminating a lot of bridges, and for that same reason it also reduces latency, so it seems obvious that this is the right approach.

There seems to be a series of assumptions here about how PCIe can be used as a fabric, and much of it is outdated.  A PCIe-based fabric that connects directly to existing devices can be constructed, and it doesn't need to use non-transparency (which seems to be an implicit assumption in this thread).   PLX is doing just that, and you can go to www.plxtech.com/expressfabric for a more in-depth explanation.

SRIO has the same drawbacks as Ethernet and InfiniBand in regards to needing additional bridges in most cases, since the devices that have a direct SRIO interface can be easily counted – and that's not many.  And SRIO doesn't even have the advantage of the nearly universal usage that Ethernet has, or the incumbency for HPCs that InfiniBand has.  So it has all of the disadvantages of the other alternatives, and none of their advantages.

This has nothing to do with the technical merits of SRIO at the SerDes or protocol level.  It is a well-defined, high-performance interconnect.  But it lost out to PCIe as the general-purpose connection back when it mattered, and the virtuous cycle that developed for PCIe made this a non-competition. You can argue about the speeds and feeds as much as you want, but as none other than the philosopher/actor Bill Murray once said, "It just doesn't matter."

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ARM Impact
TonyTib   2/27/2014 5:29:48 PM
What about the impact of ARM?  How many ARM MPUs have direct PCIe interfaces?  What happens if ARM vendors adopt SRIO?  (Probably not likely, but could happen).

PCIe has achieved its success primarily because of Intel's dominance.  If Intel loses its dominance (or, arguabley, has already lost outside of the traditional PC desktop/laptop world), then we could see changes.

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Re: ARM Impact
antoanto   2/27/2014 7:29:24 PM
It will be perfect because our architecture can be ported into RapidIO or Hypershare.

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