The AMD Ryzen 9 9950X and Ryzen 9 9900X Review: Flagship Zen 5 Soars - and Stalls
by Gavin Bonshor on August 14, 2024 9:00 AM EST- Posted in
- CPUs
- AMD
- Desktop
- Zen 5
- AM5
- Ryzen 9000
- Ryzen 9 9950X
- Ryzen 9 9900X
Core-to-Core Latency: Zen 5 Gets Weird
As the core count of modern CPUs is growing, we are reaching a time when the time to access each core from a different core is no longer a constant. Even before the advent of heterogeneous SoC designs, processors built on large rings or meshes can have different latencies to access the nearest core compared to the furthest core. This rings true especially in multi-socket server environments.
But modern CPUs, even desktop and consumer CPUs, can have variable access latency to get to another core. For example, in the first generation Threadripper CPUs, we had four chips on the package, each with 8 threads, and each with a different core-to-core latency depending on if it was on-die or off-die. This gets more complex with products like Lakefield, which has two different communication buses depending on which core is talking to which.
If you are a regular reader of AnandTech’s CPU reviews, you will recognize our Core-to-Core latency test. It’s a great way to show exactly how groups of cores are laid out on the silicon. This is a custom in-house test, and we know there are competing tests out there, but we feel ours is the most accurate to how quick an access between two cores can happen.
Looking at the above latency matrix of the Ryzen 9 9950X, we observe that the lowest latencies naturally occur between adjacent cores on the same CCX. The core pairs such as 0-1, 1-2, and 2-3 consistently show latencies in the 18.6 to 20.5 nanoseconds range. This is indicative of the fast L3 cache shared within the CCX, which ensures rapid communication between the inner cores on the same complex.
Compared to the Ryzen 9 7950X, we are seeing a slight increase in latencies within a single CCX. The SMT "advantage", where two logical cores sharing a single physical core have a lower latency, appears to be gone. Instead, latencies are consistently around 20ns from any logical core to any other logical core within a single CCX. That average is slightly up from 18ns on the 7950X, though it's not clear what the chief contributing factor is.
More significantly – and worryingly so – are the inter-CCD latencies. That is, the latency to go from a core on one CCD to a core on the other CCD. AMD's multi-CCD Ryzen designs have always taken a penalty here, as communicating between different CCDs means taking a long trek through AMD's Infinity Fabric to the IOD and back out to the other CCD. But the inter-CCD latencies are much higher here than we were expecting.
For reference, on the Ryzen 9 7950X, going to another CCD is around 76ns. But in Ryzen 9 9950X, we're seeing an average latency of 180ns, over twice the cost of the previous generation of Ryzen. Making this all the more confusing, Granite Ridge (desktop Ryzen 9000) reuses the same IOD and Infinity Fabric configuration as Raphael (Ryzen 7000) – all AMD has done is swap out the Zen 4 CCDs for Zen 5 CCDs. So by all expectations, we should not be seeing significantly higher inter-CCD latency here.
Our current working theory is that this is a side-effect of AMD's core parking changes for Ryzen 9000. That cores are being aggressively put to sleep, and that as a result, it's taking an extra 100ns to wake them up. If that is correct, then our core-to-core latency test is just about the worst case scenario for that strategy, as it's sending data between cores in short bursts, rather than running a sustained workload that keeps the cores alive over the long-haul.
At this point, we're running some additional tests on the 9950X without AMD's PPM provisioning driver installed, to see if that's having an impact. Otherwise, these high latencies, if accurate for all workloads, would represent a significant problem for multi-threaded workloads that straddle the Infinity Fabric.
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evanh - Friday, August 16, 2024 - link
Ah, right, thanks for the correction. Fingers crossed it has a rectification.jcc5169 - Friday, August 16, 2024 - link
After reading lots of other reviews, Anandtech's reviews are incomplete. This is more of an Intel counter-espionage article than anything else. You will probably need to redo these in about 4 weeks.evanh - Friday, August 16, 2024 - link
Gaming tests, on Windoze at least, have universally been below expectations. Doesn't matter which review site you read.evanh - Friday, August 16, 2024 - link
And it really is a puzzle because single core productivity and IPC testing do show excellent uplift. That should be good news for games but isn't. Why?Oxford Guy - Friday, August 16, 2024 - link
'All of the Ryzen 9000 series processors use the same AM5 socket as the previous Ryzen 7000 (Zen 4) series, which means users can use current X670E and X670 motherboards with the new chips. Unfortunately, as we highlighted in our Ryzen 7 9700X and Ryzen 5 9600X review, the X870E/X870 motherboards, which were meant to launch alongside the Ryzen 9000 series, won't be available until sometime in September.'How unfortunate is this in the big picture? Intel likes to arbitrarily obsolete the current motherboards when it releases a chip series.
ballsystemlord - Saturday, August 17, 2024 - link
@Gavin , The image for 1080p AV1 encoding, here: https://images.anandtech.com/graphs/graph21524/136...Is partially cut off. You might want to fix that.
icf80 - Saturday, August 17, 2024 - link
Is core parking affecting the inter-CCD latencies?icf80 - Sunday, August 18, 2024 - link
Does the latencies between CCDs depend on the speed of infinity fabric or DRAM settings? It would be interesting to test this. Is it possible to adjunt de IF speed?Bruzzone - Monday, August 19, 2024 - link
Don't believe everything that some PC media, stuck in their benchmarking segment caught up in their application box, then acting as a catalyst for others to shoot from the hip mimicking repeaters engaged in a false narrative promoting a herd effect reporting on Granite Ridge adoption "stalling' in sales channelsAMD relying on buyers for R9K validation ahead of Arrow there is so much back generation to sell; R7K, R5K, Raptors, Alder before Granite Ridge and Arrow producer (q4 OEM) ramp. PC market continues in a deflationary downward price spiral into q1 2025 probably all the way into summer 2025; CPU, dGPU, cases, boards you name it all has to liquidate to finance channel procurements into 2025.
R9K between Thursday and Saturday cleared down < 66% and it appears box processor got a restock on Saturday 17th. There are a lot more SI PC offered then boxed R9K CPU and those SI PC' are clearing their current run end full kit from the channel.
R9K price is held up by the channel to clear back generations R7K/R5K, Raptors, Alders and laptops wow there are a lot of laptops to clear and there are R9K CPU price premiums to margin cost offset the clearance sales. Today WW channel 9950X ask $689 to $1050, 9900X ask $499 to $782, 9700X ask $359 to $591, 9600X ask $279 to $484 so shop around if you can on geographic location.
Here is what AMD sells R9K for to volume customers which is the retail cost; 9950X = $486, 9900X = $375. 9700x = $270, 9600X = $210 so in relation AMD MSRP that is a + 33% margin across the board if there are no price premiums albeit there can be even for end user buyer beta evaluators (knowing and unknowing, voluntary and involuntary) until all the older products sells off.
Remember the AMD and Intel basic price to volume retail seller rule SO you know what the volume seller paid and in a kit purchase know you get what u negotiate. AMD CPU rule is MSRP / 3 * 1.5 is volume seller cost. For Intel its $1K AWP / 2.
I am monitoring the situation to validate R9K desktop sales out the gate were other than fleeting on initial interest.
One thing is certain through, current and back one generation AMD and Intel desktop processors and laptops are being discounted and the pricing only gets better between now and year end because the channel must liquidate current inventories to financial next generation procurements.
mb
ballsystemlord - Monday, August 19, 2024 - link
My question is, why $650 for the new R9950X? That's not competitive at all IMHO.