Does the use of data storage in constant memory provides any benefit over texture in the Pascal architecture if the data request frequency is very high among threads (every thread pick at least one data from a specific column)?
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If the expectations for constant memory usage are satisfied, the use of constant memory is a good idea in the general case. It is allowing your code to take advantage of an additional cache mechanism provided by the GPU hardware, and in so doing putting less pressure on the usage of texture by other parts of your code.
Since the constant memory and its cache, as the texture and surface memory and it is own cache are defined by the hardware Compute Capability, the target hardware should be accounted. Thus the option by constant memory and texture memory is dependent of the access pattern and the cache use, as the cache availability.
The constant memory performance is related to data broadcast among threads in a warp, so the maximum performance is achieved if all threads request the very same data address and the data is already on the cache. Thus, if in the same warp there are request to multiple address, the service is splitted in multiple requests, since it can retrive a single address per operation. If the number of splitted requests due to data retrieval from multiple addresses is too high, the texture and surface memory performance may superior over constant memory in this specific situation.. This information is detailed in the Cuda Programming Guide:
The constant memory space resides in device memory and is cached in the constant cache mentioned in Compute Capability 2.x.
A request is then split into as many separate requests as there are
different memory addresses in the initial request, decreasing
throughput by a factor equal to the number of separate requests.
The resulting requests are then serviced at the throughput of the
constant cache in case of a cache hit, or at the throughput of device
memory otherwise.
The texture memory cache is more flexible than constant memory cache. It can take advantage of readings in the same warp of address that are close together in a 2D fashion. Despite of some advantages over constant memory, in general, the texture memory should be used if the data access pattern or the data size does not follow the constant memory requirements or to make use of texture memory cache. More detailed information can be found at:
The texture and surface memory spaces
reside in device memory and are cached in texture cache, so a texture
fetch or surface read costs one memory read from device memory only on
a cache miss, otherwise it just costs one read from texture cache. The
texture cache is optimized for 2D spatial locality, so threads of the
same warp that read texture or surface addresses that are close
together in 2D will achieve best performance. Also, it is designed for
streaming fetches with a constant latency; a cache hit reduces DRAM
bandwidth demand but not fetch latency.
Reading device memory through texture or surface fetching present some
benefits that can make it an advantageous alternative to reading
device memory from global or constant memory:
- If the memory reads do not follow the access patterns that global or
constant memory reads must follow to get good performance, higher
bandwidth can be achieved providing that there is locality in the
texture fetches or surface reads;
- Addressing calculations are
performed outside the kernel by dedicated units;
- Packed data may be
broadcast to separate variables in a single operation;
- 8-bit and
16-bit integer input data may be optionally converted to 32 bit
floating-point values in the range [0.0, 1.0] or [-1.0, 1.0] (see
Texture Memory).
The developer should keep in mind that exploiting of the combination of texture memory with constant memory can be a real advantage over the preference for a single one, because it may allow to take advantage of the dedicated cache from both, since both caches have higher performance than over any data retrieved outside the cache (i.e. device memory).