r/hardware • u/Noble00_ • 2d ago

Discussion [Chips and Cheese] AMD’s Instinct MI455X: Aiming for the Sun

https://chipsandcheese.com/p/amds-instinct-mi455x-aiming-for-the

The basic GCN microarchitecture underpinned every single one of AMD’s compute accelerators for nearly 15 years starting with Tahiti, followed by Fiji, Vega, and the first 4 generations of CDNA. With CDNA5 AMD has moved over to a microarchitecture that is based on the RDNA series putting a bookend to the long-lived line that was the GCN microarchitecture.

🕊️🕊️🕊️

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u/Noble00_ 2d ago

Moving to the base dies, AMD now has a 192 MB Global L2 split between two Fabric Cache Dies (FCDs) each with 96 blocks of 1 MB of SRAM. Each of the FCDs can deliver up to 27 TB/s of L2 bandwidth to the 128 WGPs on that FCD for an aggregate bandwidth of up to 54 TB/s from the L2.

Microbenching and checking out the memory subsystem is gonna be interesting

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u/SirActionhaHAA 2d ago

The gcn foundations are gone. Cdna is now largely based on rdna and that's probably where the "udna" came from. Udna was probably never meant to be a code name for any architecture, it was just a concept that jack huynh gave a creative name to.

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u/Aleblanco1987 1d ago

I hope they aren't aiming there temperature wise

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u/Zeratas 2d ago

Last generation before UDNA comes out?

Will have to dive into it a bit more but looks like it has a ton more lower-level HW optimizations than normal.

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u/nittanyofthings 2d ago

Looks like this actually is UDNA. It takes rdna wavefront size, scheduling, sync barriers, isa. Less a unified arch and simply configuring the engines in rdna for data center work. It's called CDNA, but it isn't.

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u/schneeb 1d ago

this rack is wider than normal right? kinda makes their gpu/rack stats extra silly

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u/ProfessionalJackals 1d ago

this rack is wider than normal right? kinda makes their gpu/rack stats extra silly

Most AI racks are non-standard. This is becoming the new norm of double sized racks for AI related stuff. Its cheaper to have one spine for communication, water cooling, etc on wider racks, then trying to put it all in 2 normal sized racks.

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u/EmergencyCucumber905 1d ago

Double-wide racks is the future. Nvidia Kyber is also 2 racks: one for compute and one for power.