Thursday, March 17th 2022
AMD's Robert Hallock Confirms Lack of Manual CPU Overclocking for Ryzen 7 5800X3D
In a livestream talking about AMD's mobile CPUs with HotHardware, Robert Hallock shone some light on the rumours about the Ryzen 7 5800X3D lacking manual overclocking. As per earlier rumours, something TechPowerUp! confirmed with our own sources, AMD's Ryzen 7 5800X3D lacks support for manual CPU overclocking and AMD asked its motherboard partners to remove these features in the UEFI. According to the livestream, these CPUs are said to be hard locked, so there's no workaround when it comes to adjusting the CPU multiplier or Voltage, but at least AMD has a good reason for it.
It turns out that the 3D V-Cache is Voltage limited to a maximum of 1.3 to 1.35 Volts, which means that the regular boost Voltage of individual Ryzen CPU cores, which can hit 1.45 to 1.5 Volts, would be too high for the 3D V-Cache to handle. As such, AMD implemented the restrictions for this CPU. However, the Infinity Fabric and memory bus can still be manually overclocked. The lower Voltage boost also helps explain why the Ryzen 7 5800X3D has lower boost clocks, as it's possible that the higher Voltages are needed to hit the higher frequencies.
That said, Robert Hallock made a point of mentioning that overclocking is a priority for AMD and the Ryzen 7 5800X3D is a one off when it comes to these limitations. The reason behind this is that AMD is limited by the manufacturing technology available to the company today, but it wanted to release the technology to consumers now, rather than wait until the next generation of CPUs. In other words, this is not a change in AMD's business model, as future CPUs from AMD will include overclocking.
Hallock also explained why AMD didn't go with more cores for its first 3D V-Cache CPU and it has to do with the fact that most workloads outside of gaming don't reap much of a benefit. This is large due to how different applications use cache memory and when it comes to games, a lot of the data is being reused, which is a perfect scenario for a large cache, whereas something like video editing software, can't take advantage of a large cache in the same way. This means that AMD's secret to boosting the performance in games is that more game data ends up sitting closer to the CPU, which results in a 12 ns latency for the CPU to retrieve that data from the L3 cache, compared to 60-80 ns when the data has to be fetched from RAM. Add to this the higher bandwidth of the cache and it makes sense how the extra cache helps boost the performance in games.
For more details, please see video below. The interesting part starts around the 45:30 mark.
It turns out that the 3D V-Cache is Voltage limited to a maximum of 1.3 to 1.35 Volts, which means that the regular boost Voltage of individual Ryzen CPU cores, which can hit 1.45 to 1.5 Volts, would be too high for the 3D V-Cache to handle. As such, AMD implemented the restrictions for this CPU. However, the Infinity Fabric and memory bus can still be manually overclocked. The lower Voltage boost also helps explain why the Ryzen 7 5800X3D has lower boost clocks, as it's possible that the higher Voltages are needed to hit the higher frequencies.
Hallock also explained why AMD didn't go with more cores for its first 3D V-Cache CPU and it has to do with the fact that most workloads outside of gaming don't reap much of a benefit. This is large due to how different applications use cache memory and when it comes to games, a lot of the data is being reused, which is a perfect scenario for a large cache, whereas something like video editing software, can't take advantage of a large cache in the same way. This means that AMD's secret to boosting the performance in games is that more game data ends up sitting closer to the CPU, which results in a 12 ns latency for the CPU to retrieve that data from the L3 cache, compared to 60-80 ns when the data has to be fetched from RAM. Add to this the higher bandwidth of the cache and it makes sense how the extra cache helps boost the performance in games.
For more details, please see video below. The interesting part starts around the 45:30 mark.
222 Comments on AMD's Robert Hallock Confirms Lack of Manual CPU Overclocking for Ryzen 7 5800X3D
I do expect AM5 boards to cost more, tho.
As for this news more broadly: if it only means there's no manual, multiplier-based OC, but PBO and CO are still there ... who cares? All-core fixed-multiplier OC on Ryzen is a pretty bad idea unless you're consistently running 100% load nT workloads anyhow. There's no reason why anyone should use that over PBO and CO tuning, unless what you're going for is worse performance and higher power consumption.
But no oc on Zen 4 will be a huge disappointment for me.
"Our highest chip launches on 4/20"
Makes sense.
If we can't even try to OC is because it's already at that limit. If 1.35 is the limit is should be at something more moderate and we could use sylicon lottery to try and push it a bit further like any CPU before it.
So i assume this is just a CPU really pushed to it's limits just to compete with Intel.
Even if Alder Lake wasn't released yet, AMD would want the X3D to be as close to the 5800X clock frequencies as possible, otherwise it wouldn't make much sense in launching it.
AFAIK, the 3D cache is primarily made for Milan-X.
But knowing AGESA they have an abysmal record of keeping features consistent (especially vendors like GB that release and pull a billion beta BIOSes weekly). So if the V-cache really is that sensitive to voltage, then that sounds like a recipe for disaster..........but I wonder if it's that the cache really can't handle the voltage, or that heat density is too much under certain heavy loads?
Think Intel have had separate cache clock and voltage for like a decade now - obviously a bit more involved with V-cache but I'd fully expect this whole deal to be resolved on AM5. 5800X3D is just an experiment searching for guinea pigs
Currently on normal L3, cache freq is very closely correlated to core effective clock at all times, so curious to see if they have or will eventually decouple cache clock