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SiFive's RISC-V HiFive Unmatched Upgraded To Ship With 16GB Of RAM

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  • #21
    Originally posted by jacob View Post

    OoO has also suffered from various security issues where the re-ordering of instructions can be exploited in some cases to bypass memory protection, for example. Still, in-order CPUs are now only used in embedded applications or microcontrollers, it is unthinkable to release a general-purpose, high performance processor without OoO execution.
    Literally nothing you said here is true. OoO is not the culprit in the timing attacks you are thinking about, speculative execution and loads are. There are also application processors that are in-order, and yes they often end up in embedded scenarios, but that has more to do with the legacy of wintel than any pure deficiency of in-order designs for all personal computing.
    Last edited by microcode; 08 December 2020, 10:11 PM.

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    • #22
      Interesting.

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      • #23
        Originally posted by uid313 View Post
        4 cores is very little. All the modern ARM boards have 8 cores.
        This is a dev board, not a productivity workstation. Besides, it was only in 2017 when *all* of intel's top Core i7 chips were 4-core. There's not much of an ecosystem out there for consumer software that can leverage more than 4 cores right now. Again, plenty adequate for a dev board like this.

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        • #24
          Originally posted by microcode View Post

          Literally nothing you said here is true. OoO is not the culprit in the timing attacks you are thinking about, speculative execution and loads are. There are also application processors that are in-order, and yes they often end up in embedded scenarios.
          Technically you are correct. But 99.9% of OoO processors ever made also include speculative execution, especially speculative loads. With speculative execution the OoO shine in performance the most, and this is why it is utilized. Yes, there were few OoO CPUs made that don't have speculative execution, or limited speculation capabilities. ARM Cortex-A9 is one of very few examples.

          There are also speculative in-order cores, i.e. Cortex-A8 (2005), Mill (WIP), Intel Bonel / Saltwell (2008 / 2011), Itanium Merced and McKinley(2001) , UltraSPARC (1995), POWER6 (2007). (I only list relatively high performant designs).

          Rest of high performance CPUs, are OoO and speculative, PowerPC, POWER, Alpha, SPARC64, Intel Pentium, AMD K5, MIPS R1000, HP PA-8000, DEC Alpha, Intel Core, Almost all high performance ARM cores, etc.

          The issue is not with speculative execution itself, or OoO, but the implementation. There were serious bugs in silicon and microarchitecture design, that lead to the problems. There are OoO with and without speculation, and in-order speculative designs, that doesn't suffer from Meltdown at all. (The in-order non-speculative ones, well, they can't have issues like that either obviously).

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          • #25
            Originally posted by uid313 View Post
            4 cores is very little. All the modern ARM boards have 8 cores.
            Not true.

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            • #26
              Originally posted by Alexmitter View Post
              [ARM processors] also have branch prediction and other fancy stuff. But thats not the point with such a small series silicon by a tiny company.
              The Sifive FU540 (on the old Unleashed board) and FU740 (on the new Unmatched board) have branch prediction and other fancy stuff.

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              • #27
                Originally posted by PublicNuisance View Post
                This works out well for me. I won't be able to order one until March anyway so the delay doesn't hurt me at all and the 8GB of extra RAM is fantastic.
                They also aren't open source and blob free. While I would love to have 8 cores over 4 for me being open source/blob free is a bigger priority.
                The Sifive FU540 (on the Unleashed) and FU740 (on the Unmatched) also are not open source. Sifive's business model is licensing their cores, same as ARM. Their FE310 (microcontroller) RTL was open source, as was the FU500 (intended for FPGA use).

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                • #28
                  Side-query: How important is OoOE in compile-from-(open)-source land? How much of the benefits can be gained instead from a good compiler, with good inherent knowledge of the processor it is compiling for?

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                  • #29
                    Originally posted by torsionbar28 View Post
                    This is a dev board, not a productivity workstation. Besides, it was only in 2017 when *all* of intel's top Core i7 chips were 4-core. There's not much of an ecosystem out there for consumer software that can leverage more than 4 cores right now. Again, plenty adequate for a dev board like this.
                    Yeah, but Intel Core i7 beats this at everything and anything. This can't even compete with Intel, maybe it can wish to compete with ARM but the ARM boards have 8 cores. Even the shitty Raspberry Pi has 4 cores so this is not impressive at all.
                    If it is to be a dev board, it should probably have a mix of heterogeneous cores, such as 4 weak cores and 4 strong cores, so you can develop to take advantage of heterogeneous environments where not all cores are equal. Seems to be a pretty shitty dev board if you cant use it to develop systems for heterogeneous computing environments.

                    Originally posted by brad0 View Post

                    Not true.
                    Yes, 4 cores is very little. Pretty much all phones have 8 cores, even the cheap ones. All or most of the Snapdragon series of SoC from Qualcomm have 8 cores. The Apple A14 have 6 cores. 4 cores is little, you could buy phones many years ago with 8 cores.

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                    • #30
                      Originally posted by uid313 View Post
                      Yeah, but Intel Core i7 beats this at everything and anything. This can't even compete with Intel, maybe it can wish to compete with ARM but the ARM boards have 8 cores. Even the shitty Raspberry Pi has 4 cores so this is not impressive at all.
                      If it is to be a dev board, it should probably have a mix of heterogeneous cores, such as 4 weak cores and 4 strong cores, so you can develop to take advantage of heterogeneous environments where not all cores are equal. Seems to be a pretty shitty dev board if you cant use it to develop systems for heterogeneous computing environments.


                      Yes, 4 cores is very little. Pretty much all phones have 8 cores, even the cheap ones. All or most of the Snapdragon series of SoC from Qualcomm have 8 cores. The Apple A14 have 6 cores. 4 cores is little, you could buy phones many years ago with 8 cores.
                      I guess you simply don't get what this is. It is not your consumer grade 7nm qualcomm SoC that is dirt cheap to produce as qualcomm produces millions of those chips. This is a very expensive low number silicon production. Every mm2 of die cost them an insane amount comparably. That is what you pay for, you would be stupid if you seriously compare it to a rapsberry pi as this board is not for the hobbyist market.

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