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adds dynamic shared mem allocation to cuda kernels #413

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adds dynamic shared mem allocation to cuda kernels #413

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5919734
add dynamic shared mem allocation for hvm.cu
kings177 Aug 16, 2024
d5e3261
.gitignore autogenerated cuda headers
kings177 Aug 16, 2024
1579e64
remove unnecessary print line
kings177 Aug 16, 2024
2fa9f59
directly pass the value of shared mem to a define method
kings177 Aug 19, 2024
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3 changes: 3 additions & 0 deletions .gitignore
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Original file line number Diff line number Diff line change
Expand Up @@ -14,3 +14,6 @@ examples/**/*.cu
# nix-direnv
/.direnv/
/.envrc

# cuda header
src/shared_mem_config.h
25 changes: 24 additions & 1 deletion build.rs
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Original file line number Diff line number Diff line change
@@ -1,3 +1,5 @@
use std::process::Command;

fn main() {
let cores = num_cpus::get();
let tpcl2 = (cores as f64).log2().floor() as u32;
Expand All @@ -6,6 +8,8 @@ fn main() {
println!("cargo:rerun-if-changed=src/hvm.c");
println!("cargo:rerun-if-changed=src/run.cu");
println!("cargo:rerun-if-changed=src/hvm.cu");
println!("cargo:rerun-if-changed=src/get_shared_mem.cu");
println!("cargo:rerun-if-changed=src/shared_mem_config.h");
println!("cargo:rustc-link-arg=-rdynamic");

match cc::Build::new()
Expand All @@ -23,13 +27,32 @@ fn main() {
}

// Builds hvm.cu
if std::process::Command::new("nvcc").arg("--version").stdout(std::process::Stdio::null()).stderr(std::process::Stdio::null()).status().is_ok() {
if Command::new("nvcc").arg("--version").stdout(std::process::Stdio::null()).stderr(std::process::Stdio::null()).status().is_ok() {
if let Ok(cuda_path) = std::env::var("CUDA_HOME") {
println!("cargo:rustc-link-search=native={}/lib64", cuda_path);
} else {
println!("cargo:rustc-link-search=native=/usr/local/cuda/lib64");
}

// Compile get_shared_mem.cu
if let Ok(output) = Command::new("nvcc")
.args(&["src/get_shared_mem.cu", "-o", "get_shared_mem"])
.output()
.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))
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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

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true, that sounds cleaner indeed, will change it to that

.expect("Failed to write shared_mem_config.h");
} else {
println!("cargo:warning=\x1b[1m\x1b[31mWARNING: Failed to get shared memory size. Using default value.\x1b[0m");
}
} else {
println!("cargo:warning=\x1b[1m\x1b[31mWARNING: Failed to compile or run get_shared_mem.cu. Using default shared memory value.\x1b[0m");
}

// Clean up temporary executable
let _ = std::fs::remove_file("get_shared_mem");

cc::Build::new()
.cuda(true)
.file("src/run.cu")
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24 changes: 24 additions & 0 deletions src/get_shared_mem.cu
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Original file line number Diff line number Diff line change
@@ -0,0 +1,24 @@
#include <cuda_runtime.h>
#include <cstdio>

int main() {
int device = 0;
cudaDeviceProp prop;
cudaGetDeviceProperties(&prop, device);

size_t sharedMemPerBlock = prop.sharedMemPerBlock;
int maxSharedMemPerBlockOptin;
cudaDeviceGetAttribute(&maxSharedMemPerBlockOptin, cudaDevAttrMaxSharedMemoryPerBlockOptin, device);

size_t maxSharedMem = (sharedMemPerBlock > (size_t)maxSharedMemPerBlockOptin) ? sharedMemPerBlock : (size_t)maxSharedMemPerBlockOptin;

// Subtract 3KB (3072 bytes) from the max shared memory as is allocated somewhere else
maxSharedMem -= 3072;
Comment on lines +15 to +16
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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.

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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.


// Calculate the hex value
unsigned int hexValue = (unsigned int)(maxSharedMem / 12);

printf("0x%X", hexValue);

return 0;
}
10 changes: 8 additions & 2 deletions src/hvm.cu
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Expand Up @@ -126,9 +126,15 @@ struct RBag {
Pair lo_buf[RLEN];
};

#include "shared_mem_config.h"

#ifndef HVM_SHARED_MEM
#define HVM_SHARED_MEM 0x2000 // Default value
#endif

// Local Net
const u32 L_NODE_LEN = 0x2000;
const u32 L_VARS_LEN = 0x2000;
const u32 L_NODE_LEN = HVM_SHARED_MEM;
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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.

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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)

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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"

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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.

const u32 L_VARS_LEN = HVM_SHARED_MEM;
struct LNet {
Pair node_buf[L_NODE_LEN];
Port vars_buf[L_VARS_LEN];
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