41–50 of 143 posts
Wait, PCIe bandwidth is higher than memory bandwidth now? That's bonkers, when did that happen? I haven't been keeping up. Just looked at the i9-14900k and I guess it's true, but only if you add all the PCIe lanes together. I'm sure there are other chips where it's even more true. Crazy!
Wait, PCIe bandwidth is higher than memory bandwidth now? That's bonkers, when did that happen? I haven't been keeping up. Just looked at the i9-14900k and I guess it's true, but only if you add all the PCIe lanes together. I'm sure there are other chips where it's even more true. Crazy!
on server chips it's kind of ridiculous. 5th gen Epyc has 128 lanes of PCIEx5 for over 1TB/s of pcie bandwith (compared to 600GB/s RAM bandwidth from 12 channel ddr5 at 6400)
Unless we are considering both read and write bandwidth, but that seems strange to compare to memory read bandwidth.
Wait, PCIe bandwidth is higher than memory bandwidth now? That's bonkers, when did that happen? I haven't been keeping up. Just looked at the i9-14900k and I guess it's true, but only if you add all the PCIe lanes together. I'm sure there are other chips where it's even more true. Crazy!
DDR5-8000 is 64GB/s per channel. Desktop CPUs have two channels. PCI-E 5.0 in x16 is 64GB/s. Desktops have one x16.
Wait, PCIe bandwidth is higher than memory bandwidth now? That's bonkers, when did that happen? I haven't been keeping up. Just looked at the i9-14900k and I guess it's true, but only if you add all the PCIe lanes together. I'm sure there are other chips where it's even more true. Crazy!
"No." DDR5-8000 is 64GB/s per channel. Desktop CPUs have two channels. PCI-E 5.0 in x16 is 64GB/s. Desktops have one x16.
Earlier quoted context omitted.
That doesn’t sound like the intended meaning of “on disk”.
Kernel doesn't really care about "on disk", it cares about "on filesystem". The "on disk" distinction is a simplification.
Earlier quoted context omitted.
on server chips it's kind of ridiculous. 5th gen Epyc has 128 lanes of PCIEx5 for over 1TB/s of pcie bandwith (compared to 600GB/s RAM bandwidth from 12 channel ddr5 at 6400)
Your math is a bit off. 128 lanes gen5 is 8 times x16, which has a combined theoretical bandwidth of 512GB/s, and more like 440GB/s in practice after protocol overhead. Unless we are considering both read and write bandwidth, but that seems strange to compare to memory read bandwidth.
Earlier quoted context omitted.
Your math is a bit off. 128 lanes gen5 is 8 times x16, which has a combined theoretical bandwidth of 512GB/s, and more like 440GB/s in practice after protocol overhead. Unless we are considering both read and write bandwidth, but that seems strange to compare to memory read bandwidth.
People like to add read and write bandwidth for some silly reason. Your units are off, too, though: gen 5 is 32 GT/s, meaning 64 GB/s (or 512 gigabits per second) each direction on an x16 link.
Earlier quoted context omitted.
"No." DDR5-8000 is 64GB/s per channel. Desktop CPUs have two channels. PCI-E 5.0 in x16 is 64GB/s. Desktops have one x16.
Hmm, Intel specs the max memory bandwidth as 89.6 GB/s. DDR5-8000 would be out of spec. But I guess it's pretty common to run higher specced memory, while you can't overclock PCIe (AFAIK?). Even so I guess my math was wrong, it doesn't quite add up to more than memory bandwidth. But it's pretty darn close!
Zen 5 can hit that (and that's what I run), and Arrow Lake can also.
The recommended from AMD on Zen 4 and 5 is 6000 (or 48x2), for Arrow Lake is 6400 (or 51.2x2); both of them continue increase in performance up to 8000, both of them have extreme trouble going past 8000 and getting a stable machine.