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Your first point is an implementation detail. Why couldn't CPU RAM be used as well in a GPU database system? Re CPU vs GPU performance you are neglecting the f

by tmostak 10y ago

Your first point is an implementation detail. Why couldn't CPU RAM be used as well in a GPU database system? Re CPU vs GPU performance you are neglecting the fact that GPU RAM can be an order-of-magnitude faster than CPU RAM, not to mention the fact that complex queries can often become compute bound (geospatial queries are a prominent example).

valarauca1 10y ago
Why couldn't CPU RAM be used as well in a GPU database system? There is no market demand for this currently. GPU's don't need advanced MMU's because nobody wants them. The same is true for PCIe data loading. CPU vs GPU performance you are neglecting the fact that GPU RAM can be an order-of-magnitude faster than CPU RAM, No I'm not. If your data set can remain in GPU ram long term yes there is a big performance speed up. The problem here (as I outlined before) 1. GPU MMU's are less advanced, so they don't handle transactions well (see above comments). 2. As you can't perform transactions efficiently, you need read only data. Which is possible but many databases aren't read only, or databases NOT being written too are rare. 3. Ensuring your full dataset can fit in GPU memory (typically <20GB) is a damning limitation. Streaming data into the GPU is rather sloppy and limits compute though-put.
nine_k 10y ago
The CPU / RAM is a bottleneck between the persistent storage and the fast GPU. There's a well-known way to increase network throughput and reduce latency by running a whole dedicated IP stack + hardware driver in the user space of the process that needs it. This removes the bottleneck of the OS kernel. I wonder if there's a way to remove the bottleneck in the GPU case by something similar, by dedicating a piece of hardware to the SSD interconnect without having a CPU as an intermediary. AFAICT you still cannot DMA from a disk directly to GPU RAM, even though you have enough PCIe lanes coming to the GPU. Is this true? If so, can it change in a way that is still compatible with traditional, "normal" operation of the PC architecture?

by tmostak 10y ago

valarauca1 10y ago

Why couldn't CPU RAM be used as well in a GPU database system? There is no market demand for this currently. GPU's don't need advanced MMU's because nobody wants them. The same is true for PCIe data loading. CPU vs GPU performance you are neglecting the fact that GPU RAM can be an order-of-magnitude faster than CPU RAM, No I'm not. If your data set can remain in GPU ram long term yes there is a big performance speed up. The problem here (as I outlined before) 1. GPU MMU's are less advanced, so they don't handle transactions well (see above comments). 2. As you can't perform transactions efficiently, you need read only data. Which is possible but many databases aren't read only, or databases NOT being written too are rare. 3. Ensuring your full dataset can fit in GPU memory (typically <20GB) is a damning limitation. Streaming data into the GPU is rather sloppy and limits compute though-put.

nine_k 10y ago

The CPU / RAM is a bottleneck between the persistent storage and the fast GPU. There's a well-known way to increase network throughput and reduce latency by running a whole dedicated IP stack + hardware driver in the user space of the process that needs it. This removes the bottleneck of the OS kernel. I wonder if there's a way to remove the bottleneck in the GPU case by something similar, by dedicating a piece of hardware to the SSD interconnect without having a CPU as an intermediary. AFAICT you still cannot DMA from a disk directly to GPU RAM, even though you have enough PCIe lanes coming to the GPU. Is this true? If so, can it change in a way that is still compatible with traditional, "normal" operation of the PC architecture?