Can 9-9-9-24 Memory be used in place of 11-11-11-35



  • I hope one of the hardware experts here can help me out.

    The motherboard specifications say:
    System Memory:
    Memory Capacity: Up to 8GB Unbuffered non-ECC SO-DIMM, DDR3-1600MHz, in 2 DIMM slots
    Memory Type: 1600/1333/1066MHz DDR3 SO-DIMM, 204-pin gold-plated DIMMs
    DIMM Sizes: 2GB, 4GB
    Memory Voltage: 1.35 V

    I am considering using the following memory

    Corsair Vengeance 8GB (2x4GB) DDR3L
    1600MHz CL9 1.35v SODIMMs
    (CMSX8GX3M2B1600C9)

    Memory Type DDR3L
    Package Memory Format SODIMM
    Package Memory Pin 204
    Memory Size 8GB Kit (2 x 4GB)
    SPD Latency 9-9-9-24
    SPD Speed 1600MHz
    SPD Voltage 1.35V / 1.5V
    Speed Rating PC3-12800 (1600MHz)
    Tested Latency 9-9-9-24
    Tested Speed 1600MHz
    Tested Voltage 1.35V

    From asking around the forum I have only been able to find someone using
    memory with SPD Latency 11-11-11-35 (and other specs kept constant)

    Is it likely that the faster 9-9-9-24 will be OK, or am I likely to experience problems.

    Any help would be much appreciated.



  • Yes, it will work fine at slower timings.

    I'm fairly certain that the board will actually run the memory at 9-9-9-24 if that's what is embedded in the SPD on the stick(s).



  • @dreamslacker:

    Yes, it will work fine at slower timings.

    I'm fairly certain that the board will actually run the memory at 9-9-9-24 if that's what is embedded in the SPD on the stick(s).

    Thanks… that's what I was thinking as well, but I don't do a lot of hardware... just when I need to build or something needs fixing.

    I guess I'll find out.



  • You really DON'T need  ultra high spec ram if this is just a pfsense box unless its a virtualized  environment.  The speed difference  between  cl11- and cl9  really isn't big enough  to even notice  in this application.  Even if you're WAN were 1-10Gbps  this won't put a load on your ram anway.  If speed is you're goal use a ssd and atleast a dual core atom or above c2558/c2758 or even i3/i5 braswell/  pfsense isn't ram dependent it barely uses 2-4gb



  • If you have 2GiB of states(1mil states) and 8MiB of L3 cache, which can only hold a maximum of 4,096 states, you'll be hitting memory all of the time. Normally cache misses that go out to memory take about 300 clock cycles, but that's because the 11-11-11 cycle memory normally takes about that many CPU cycles. Going from 11 to 9 cycles will be an 18% improvement in memory latency. This means dropping cache misses from 300 cycles to about 250 cycles. It's not nothing.

    What you're thinking about is most benchmarks, which use a lot of sequential memory access and has high amounts of cache hits does not benefit much from low latency. Workloads with lots of random memory access and low cache hit rates benefit almost directly with lower latency memory. That being said, under most workloads only a small number of flows consume most of the bandwidth. This also is directly related with cache hits. Just make sure your CPU has enough L3 cache, like a Xeon with 20MiB will be able to handle your planned number of states, but don't exclude low latency memory from your build thinking it's a waste.

    I was just watching a few year old video that was saying one of the issue in FreeBSD's PF is it's well factored. Because they wrote the code with best practice in mind, the layers are not leaky and this means at least 3 layers of indirection, which almost always results in three cache miss per packet, and there's still 5 more layers of the network stack to get through once it gets past that point.



  • Did you settle on RAM? Been following your choices in your build and would be interested to see how it comes together.



  • @krackpot:

    Did you settle on RAM? Been following your choices in your build and would be interested to see how it comes together.

    I'll let you know how it works when I get the rest of the stuff, still waiting for the MB and PS so it will be awhile before I get to building it, but I did buy the Corsair Vengeance 9-9-9-24.  It was on sale, and the cheapest that my local store had to offer.



  • @guardian:

    @krackpot:

    Did you settle on RAM? Been following your choices in your build and would be interested to see how it comes together.

    I'll let you know how it works when I get the rest of the stuff, still waiting for the MB and PS so it will be awhile before I get to building it, but I did buy the Corsair Vengeance 9-9-9-24.  It was on sale, and the cheapest that my local store had to offer.

    I promised to report back:  The 9-9-9-24 Memory works just fine.

    I did however build a different system… went with a little package from China due to cost.  You can see what I got here.

    https://forum.pfsense.org/index.php?topic=113308.msg638930#msg638930

    So I have one of the 4GB modules from this set:
    Corsair Vengeance 8GB (2x4GB) DDR3L
    1600MHz CL9 1.35v SODIMMs
    (CMSX8GX3M2B1600C9)
    and a:
    Samsung 850 EVO 120GB SSD