Comments on: Grant Martin on Manycore Multicore MPSoC AMP SMP Multi-X… http://jakob.engbloms.se/archives/114?&owa_medium=feed&owa_sid= Computer Technology: Simulation, Virtualization, Virtual Platforms, Embedded, Multicore and Multiprocessing (by Jakob Engblom) Thu, 12 Jan 2012 21:54:16 -0800 hourly 1 http://wordpress.org/?v=3.3.1 By: Jakob http://jakob.engbloms.se/archives/114/comment-page-1#comment-1594 Jakob Sun, 04 May 2008 19:48:57 +0000 http://jakob.engbloms.se/?p=114#comment-1594 Good points in the debate -- if only we had somewhere to keep them in a coherent manner for the community to discuss... Anycase, I might have overstated my case in the original post. Basically, I do not think that numbers alone are a useful indicator of the nature of a particular beast (chip design). The homogeneous/heterogeneous nature is very much more important, and the particular nature of the cores included. I agree that a 100-core or 1000-core chip IS qualitatively different from a 10-core chip, since it poses a very different programming and design challenge. But I have a feeling that that difference is exactly what we want to capture in a good taxonomy, and the fact that a design gets to 1000 cores is going to be due to some design aspect of it that makes that many cores feasible. And those design aspects are going to be very different from the choices made for a 10-core chip. I guess in the end, I think that core count is a visible but secondary outcome of the deeper more interesting design decisions made. Just saying that "manycore is >= 100 cores" is not helpful, we need to express how the chip got to 100 cores. In the old world of servers, before Multicore, it used to be said that as processor counts climbed from 4 to 8 to 32 to 128, the processors became more or less free and the interconnect absolutely dominated system cost. I think similar economics and laws are waiting to be discovered in what people are desinging today in what for lack of a better term has to be called MPSoC, multiprocessor systems on chips. Good points in the debate — if only we had somewhere to keep them in a coherent manner for the community to discuss…

Anycase, I might have overstated my case in the original post. Basically, I do not think that numbers alone are a useful indicator of the nature of a particular beast (chip design). The homogeneous/heterogeneous nature is very much more important, and the particular nature of the cores included.

I agree that a 100-core or 1000-core chip IS qualitatively different from a 10-core chip, since it poses a very different programming and design challenge. But I have a feeling that that difference is exactly what we want to capture in a good taxonomy, and the fact that a design gets to 1000 cores is going to be due to some design aspect of it that makes that many cores feasible. And those design aspects are going to be very different from the choices made for a 10-core chip.

I guess in the end, I think that core count is a visible but secondary outcome of the deeper more interesting design decisions made. Just saying that “manycore is >= 100 cores” is not helpful, we need to express how the chip got to 100 cores.

In the old world of servers, before Multicore, it used to be said that as processor counts climbed from 4 to 8 to 32 to 128, the processors became more or less free and the interconnect absolutely dominated system cost. I think similar economics and laws are waiting to be discovered in what people are desinging today in what for lack of a better term has to be called MPSoC, multiprocessor systems on chips.

]]> By: Grant Martin http://jakob.engbloms.se/archives/114/comment-page-1#comment-1589 Grant Martin Sat, 03 May 2008 22:31:53 +0000 http://jakob.engbloms.se/?p=114#comment-1589 Jakob, thanks for the kind words. Your blog is also valued and on my bookmarks for regular reading. However, I don't really agree with you that numbers don't matter in the N-core discussions. But it may be that numbers matter more in the heterogeneous N-core systems and less in the homogeneous N-core systems. The 2-core laptop and 100+ core chip for a large network system will tend to be homogeneous, in that all cores (or almost all cores - the 100+ core chip for networking may have some control cores and a lot of packet crunching cores), even if tuned to the application, will tend to be the same. In the heterogeneous asymmetric multiprocessing cell phones, iPhones, etc., most processors are different ASIPs for different applications. The homogeneous style tends to a step and repeat approach, and as technology proceeds, it is indeed true that 2,4,8, 16, 32, 64, 128, ..... cores, all the same, may really fall into an evolving single class of multicore architectures. Then, I agree with Jakob that other architectural concerns such as memory systems, interconnect, etc. may be the profound differentiators. But heterogeneous AMP multicore devices are different enough from the homogeneous world that I think numbers matter. Here I see a profound difference between 1-a few 10's of different ASIPs on a die, and 100's or 1000's of different ASIPs on a single die. Here it seems to me that something profoundly different may happen in our design approach as the numbers climb. No stepping and repeating will be possible here! Right now, I just don't know where the dividing line is, or if we will discover it only post facto. But a good debate - ideally one we should be conducting on a taxonomy site if one gets started! Jakob, thanks for the kind words. Your blog is also valued and on my bookmarks for regular reading. However, I don’t really agree with you that numbers don’t matter in the N-core discussions. But it may be that numbers matter more in the heterogeneous N-core systems and less in the homogeneous N-core systems. The 2-core laptop and 100+ core chip for a large network system will tend to be homogeneous, in that all cores (or almost all cores – the 100+ core chip for networking may have some control cores and a lot of packet crunching cores), even if tuned to the application, will tend to be the same. In the heterogeneous asymmetric multiprocessing cell phones, iPhones, etc., most processors are different ASIPs for different applications. The homogeneous style tends to a step and repeat approach, and as technology proceeds, it is indeed true that 2,4,8, 16, 32, 64, 128, ….. cores, all the same, may really fall into an evolving single class of multicore architectures. Then, I agree with Jakob that other architectural concerns such as memory systems, interconnect, etc. may be the profound differentiators.

But heterogeneous AMP multicore devices are different enough from the homogeneous world that I think numbers matter. Here I see a profound difference between 1-a few 10′s of different ASIPs on a die, and 100′s or 1000′s of different ASIPs on a single die. Here it seems to me that something profoundly different may happen in our design approach as the numbers climb. No stepping and repeating will be possible here! Right now, I just don’t know where the dividing line is, or if we will discover it only post facto.

But a good debate – ideally one we should be conducting on a taxonomy site if one gets started!

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