Performance Benefits of TS on DIMM

The reduction in guardband that TS on DIMM offers over existing methods gives it a performance edge in both bandwidth as well as benchmark scores when running high-bandwidth applications. For example, when using an OpenGL benchmark on 1 GB DDR2-667 SO-DIMMs in dual channel mode, lab data showed that for every degree C of guardband removed, the system saw up to 220 MB/s bandwidth improvement per degree C, as shown in Figure 7. Since TS on DIMM typically saves ~15°C of guardband over existing methods when running a high-bandwidth application at room temperature, and at 220 MB/s per degree C, the total bandwidth recovered with TS on DIMM can be approximately 3 GB/s for this particular application, which is 30% of the theoretical maximum bandwidth for this system and memory configuration. This bandwidth recovery assumes that the workload running on the system could utilize more bandwidth if allowed, and the bandwidth recovered is also dependent on the application used and the system configuration.

Figure 7: Bandwidth recovered per degree of guardband removed
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Due to the increased bandwidth per degree C of guardband savings, benchmark scores also show improvements with TS on DIMM, as shown in Figure 8. (Benchmark score recovery is dependent on system, memory, and software configuration.) Using the same 1 GB, DDR2-667 SO-DIMMs in dual channel mode as described above, for every degree C of guardband removed, the system saw ~3.3 frames per second per degree C for a particular OpenGL application, and up to 13 3DMarks score recovery with 3DMark 03 per degree C. Again, since TS on DIMM typically saves ~15°C over existing methods, that results in an approximately 50 frames per second improvement as well as about a 200 3DMarks score improvement with these applications. Results may vary with different applications and different system configurations.

Figure 8: Benchmark scores recovered per degree of guardband removed
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To further understand how the reduction in guardband impacts bandwidth availability, let’s look at the thermal study from earlier in this paper and determine where TS on DIMM would throttle the worst-case 1 GB SO-DIMM module in comparison to DT in SPD. Please see Figure 9 below (temperature and bandwidth data is dependent on system, memory, and software configuration).

Figure 9: Guardband comparison between TS on DIMM and DT in SPD
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The graph above indicates DT in SPD would throttle when the DRAM temperature reaches 70°C (bandwidth available is 2.5 GB/s) while TS on DIMM would throttle only at 79°C (enabling memory bandwidth of 4.5 GB/s). The results clearly show that the reduction in guardband directly impacts bandwidth availability as the temperature of the DIMM reaches and exceeds 60°C at a room ambient temperature of 25°C (or 70°C if the ambient temperature is 35°C).

Other Benefits of TS on DIMM

Aside from the performance benefits mentioned above, TS on DIMM offers other benefits over existing methods. First, since the thermal sensor is measuring true operating temperature, it is able to help protect the DRAM cases from exceeding their maximum specifications even if an outside source is heating the DIMMs. For example, if a fan breaks or if the notebook is sitting in direct sunlight, the thermal sensor is always monitoring the DRAM temperatures and if they exceed the critical trip point, the chipset will throttle the memory traffic and protect the DRAMs.

With the existing methods of temperature prediction based on memory traffic alone, the chipset has no idea if some abnormality is causing the DRAM temperatures to rise beyond their specifications. Since TS on DIMM is monitoring the temperature of the memory, it also provides a way for controlling notebook skin temperatures. Keeping memory within certain thermal limits will also help keep skin temperatures within certain thermal limits.