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

By: Gionatan Danti (g.danti.delete@this.assyoma.it), December 9, 2022 12:31 am
Room: Moderated Discussions
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?

If I remember correctly, AMD L3 bandwidth result is (roughly) per-core, scaling with multiple threads much more readily than DRAM. In other words, aggregate per-chip L3 bandwidth should be much higher than DRAM bandwidth.

Moreover, a shared L3 cache has lower latency and provides an on-chip "synchronization point" between multiple cores (without forcing per-core communication via DRAM).

Regards.
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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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