What happens when DRAM has more bandwidth than Layer 3 cache?

By: Etienne (etienne_lorrain.delete@this.yahoo.fr), December 8, 2022 8:05 am
Room: Moderated Discussions
Michael S (already5chosen.delete@this.yahoo.com) on December 8, 2022 7:32 am wrote:
> Etienne (etienne_lorrain.delete@this.yahoo.fr) on December 8, 2022 6:20 am wrote:
> > Looks like my AMD Ryzen 9 7950x has a L3 cache bandwidth of 63.9 GB/s, my current DRAM DDR5
> > has either 49.6 GB/s (Jedec) or 52.5 GB/s (AMD Expo) measured by memtest86 UEFI.
> > It seems some companies are increasing DRAM bandwidth: 8Gbps DDR5.
> >
> > I assume latency to L3 cache is still probably better than latency to
> > DRAM, but in simple terms, do we still need L3 cache in processors?
>
> 63.9 GB/s = 14.2 B/clock sounds low.
> For Zen3 on 7/9 parts AMD claims 32B/clock read + 32B/clock write. For each CCD.
> Supposedly, Zen4 is similar.
>

Possibly due to the CPU frequency reported by memtest86 of 4500 MHz, assuming it measured the L3 bandwidth at that frequency...
There is so many options to configure the UEFI BIOS, that is just "load optimised default", and it seems I need even some modifications from that to get a working machine (i.e. able to compile android or Linux distributions from scratch...)
DRAM seem working on multiple hours tests, still fighting "no wakeup" after "power spikes" from stressapptest, but the PC begin to work (for my definition of working, I am not an overclocker, I want stable for hours...)
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TopicPosted ByDate
What happens when DRAM has more bandwidth than Layer 3 cache?Etienne2022/12/08 06:20 AM
  What happens when DRAM has more bandwidth than Layer 3 cache?Simon Farnsworth2022/12/08 07:22 AM
    bandwidth*delay productMichael S2022/12/08 08:06 AM
    What happens when DRAM has more bandwidth than Layer 3 cache?---2022/12/08 10:44 AM
      What happens when DRAM has more bandwidth than Layer 3 cache?blaine2022/12/08 05:07 PM
  What happens when DRAM has more bandwidth than Layer 3 cache?Michael S2022/12/08 07:32 AM
    What happens when DRAM has more bandwidth than Layer 3 cache?Etienne2022/12/08 08:05 AM
      What happens when DRAM has more bandwidth than Layer 3 cache?Michael S2022/12/08 08:13 AM
        What happens when DRAM has more bandwidth than Layer 3 cache?Etienne2022/12/08 01:56 PM
  What happens when DRAM has more bandwidth than Layer 3 cache?Peter E. fry2022/12/08 08:20 AM
  Programs do not see bandwidth. Programs only see latency. Heikki Kultala2022/12/08 08:26 AM
    Programs do not see bandwidth. Programs only see latency. Chester2022/12/08 11:07 AM
  What happens when DRAM has more bandwidth than Layer 3 cache?Doug S2022/12/08 09:31 AM
  What happens when DRAM has more bandwidth than Layer 3 cache?---2022/12/08 10:32 AM
    What happens when DRAM has more bandwidth than Layer 3 cache?Michael S2022/12/08 02:42 PM
      What happens when DRAM has more bandwidth than Layer 3 cache?---2022/12/08 03:54 PM
        What happens when DRAM has more bandwidth than Layer 3 cache?Anon2022/12/20 06:46 AM
  What happens when DRAM has more bandwidth than Layer 3 cache?Andrey2022/12/08 03:10 PM
    What happens when DRAM has more bandwidth than Layer 3 cache?Etienne2022/12/14 03:20 AM
  What happens when DRAM has more bandwidth than Layer 3 cache?Gionatan Danti2022/12/09 12:31 AM
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