adds dynamic shared mem allocation to cuda kernels #413
Conversation
kings177
requested review from
VictorTaelin,
developedby and
enricozb
and removed request for
enricozb
| // Subtract 3KB (3072 bytes) from the max shared memory as is allocated somewhere else | ||
| maxSharedMem -= 3072; |
There was a problem hiding this comment.
How did you compute this? I think this is from the automatic variables in some of the kernels. I think overall this is a fine approach for now but if we change the 3KB alloc in the runtime this will have to change too.
There was a problem hiding this comment.
the sum of the alloc size of some local shared arrays is roughly ~3KB, i know that this is not the perfect way to do this, but it works for now.
| // Local Net | ||
| const u32 L_NODE_LEN = 0x2000; | ||
| const u32 L_VARS_LEN = 0x2000; | ||
| const u32 L_NODE_LEN = HVM_SHARED_MEM; |
There was a problem hiding this comment.
Aren't there places in the code that expect L_NODE_LEN to have this exact value?
If you change it I think we'll start to get either memory leaks, out of bounds access or non local memory use.
There was a problem hiding this comment.
Also, if this number is smaller then default, the programs compiled by bend won't run.
If it's smaller the performance will also tank incredibly fast. (see the issue where someone halved this number and got worse performamce than in the cpu)
There was a problem hiding this comment.
Aren't there places in the code that expect L_NODE_LEN to have this exact value?
i wouldn't say that it expects to have this value, but rather that it expects to have the numbers of a device with 8.9 of compute capability, but then again, this is not a general optimization of the CUDA version, this is just to make the allocation of shared mem on local net dynamic, so that users can install the hvm without having to manually change it on the hvm.cu, the rest of the code is still the same, made with the numbers of a 4090 in mind. We can slowly improve the code to make it device based, instead of hard-coded to the specs of a 4090.
Also, if this number is smaller then default, the programs compiled by bend won't run.
can you show me an example of what was ran and what was the device/numbers used when this happened?
If it's smaller the performance will also tank incredibly fast. (see the issue where someone halved this number and got worse performamce than in the cpu)
i mean, that's of course, if you give it less memory, it will have less memory, besides the fact that the rest of the code is 'optimized' for a 4090.
we can like, whenever someone installs it using a GPU with <99KB of max shared mem per block, we give a warning saying something along the lines of:
"HVM is currently optimized to run on devices with >=96KB of max shared mem, please be aware that your GPU performance will be reduced dramatically"
There was a problem hiding this comment.
can you show me an example of what was ran and what was the device/numbers used when this happened?
Also, if this number is smaller then default, the programs compiled by bend won't run.
can you show me an example of what was ran and what was the device/numbers used when this happened?
The number of nodes in the local buffer determines the maximum size of hvm definitions. If we decrease L_NODE_LEN then Bend also needs to generate programs with smaller maximum definition size.
build.rs
Outdated
| .and_then(|_| Command::new("./get_shared_mem").output()) { | ||
| if output.status.success() { | ||
| let shared_mem_str = String::from_utf8_lossy(&output.stdout).trim().to_string(); | ||
| std::fs::write("src/shared_mem_config.h", format!("#define HVM_SHARED_MEM {}", shared_mem_str)) |
There was a problem hiding this comment.
Instead of writing it to a build generated file, can't we just set a define flag, like we do for the number of cores? It's prpbably possible with nvcc as well
There was a problem hiding this comment.
true, that sounds cleaner indeed, will change it to that
with this hvm.cu should work virtually on every NVIDIA GPU out there (assuming 5.0 CC and above). it dynamically allocates shared memory based on the GPU's capabilities, specifically 3072 less bytes than the max opt-in shared mem available, as some shared arrays use roughly (a little bit less than) that amount of shared mem.
since shared mem allocation needs to be known at compile time,
get_shared_mem.cucalculates the available shared mem in build time, which is ran bybuild.rsthat then generates a header fileshared_mem_config.hwith the correct hex value for the local net.Closes: #283 and #314 (supposedly)