Threadripper launched a little over a month ago, and since launch, we have had time to play around with AMD's new beast of a CPU. Threadripper CPUs connect two dies together with an Infinity Fabric that operates over 100GB/s bi-directionally. This die to die connection is what makes it possible for Threadripper CPUs to carry so many cores and threads and at an affordable price point, but they also introduce some variability when it comes to performance.
AMD counters this by adding in additional hardware modes, which can easily be accessed through Windows or BIOS, and they can have a significant enough impact on performance depending on what tasks the CPU is handling. We will test out Threadripper's hardware modes, more specifically memory access modes (Local and Distributed), SMT, and the unique Legacy Mode.
AMD has given us a decent amount of information on the memory access and Legacy modes, and we all know what SMT does (two threads per core). AMD actually provides two basic modes of operation; a Creator Mode (default) and a Gaming Mode, and today we will evaluate them and all the other possible hardware modes.
Threadripper allows you to configure memory access modes in either Distributed mode (Uniform Memory Access/UMA) or Local mode (Non-Uniform Memory Access /NUMA). UMA mode evenly distributes memory transactions across all memory channels, and it provides higher bandwidth but also higher latency. NUMA mode allows individual dies to prioritize memory access to cores nearest to physical DIMMs, and while this results in slightly lower bandwidth, it also lowers latency.
Memory access modes here can have a big impact, especially when it comes to switching between gaming and content creation. In Local mode, AMD says that the OS is hinted that an application should stay in one die until it's full, which should increase performance for those types of loads.
Simultaneous Multi-Threading (SMT) is what produces 32 threads from 16 cores. It allows the parallel assignment of two threads to a single core. SMT is excellent when you need more threads, but when the workload actually only uses about half or less of your available threads, it can help a lot to turn it off and allow one core per thread. For many years it was known that SMT or what Intel calls Hyper-Threading (HT), wasn't helpful in gaming, and could be counterintuitive. We also know from Ryzen launch that turning SMT off can produce gains in games and some applications, so we will investigate that here as well.
You can toggle SMT, memory modes, and a Legacy Compatibility mode inside the Ryzen Master Utility. All these modes require a restart, but with the speed of NVMe drives and three M.2 ports, a restart should be the least of your worries (except for Windows Update). Legacy compatibility mode does something different; it disables one of the two dies but maintains quad channel memory support, and puts the CPU into NUMA memory access mode.
AMD found that this mode was best for many games, and it puts the Threadripper 1950X on par with the 1800X when it comes to performance. It also helps to avoid issues with games or programs that might not be able to use more cores.
AMD did put out its internal results from UMA vs. NUMA memory access modes at 3200MHz, and we can see that while latency goes down in NUMA mode, so does bandwidth. AMD also made a chart of a few games and what they prefer, as depending on what they prefer, they could like NUMA over UMA (Lower memory latency), SMT ON vs. SMT OFF (Higher core counts), or Legacy Mode (Lower core-to-core latency).
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