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YJIT: Cache Context decoding (#11680)

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Takashi Kokubun 2024-09-25 09:18:13 -07:00 • committed by GitHub
parent a6ea4ddb4e
commit 505206b8ac
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GPG key ID: B5690EEEBB952194
Notes: git 2024-09-25 16:18:33 +00:00 
Merged-By: maximecb <maximecb@ruby-lang.org>
2 changed files with 71 additions and 22 deletions
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91
yjit/src/core.rs
View file

@ -870,16 +870,23 @@ enum CtxOp {
}
// Number of entries in the context cache
const CTX_CACHE_SIZE: usize = 1024;
const CTX_ENCODE_CACHE_SIZE: usize = 1024;
const CTX_DECODE_CACHE_SIZE: usize = 1024;
// Cache of the last contexts encoded
// Empirically this saves a few percent of memory
// Cache of the last contexts encoded/decoded
// Empirically this saves a few percent of memory and speeds up compilation
// We can experiment with varying the size of this cache
pub type CtxCacheTbl = [(Context, u32); CTX_CACHE_SIZE];
static mut CTX_CACHE: Option<Box<CtxCacheTbl>> = None;
pub type CtxEncodeCache = [(Context, u32); CTX_ENCODE_CACHE_SIZE];
static mut CTX_ENCODE_CACHE: Option<Box<CtxEncodeCache>> = None;
// Cache of the last contexts encoded/decoded
// This speeds up compilation
pub type CtxDecodeCache = [(Context, u32); CTX_DECODE_CACHE_SIZE];
static mut CTX_DECODE_CACHE: Option<Box<CtxDecodeCache>> = None;
// Size of the context cache in bytes
pub const CTX_CACHE_BYTES: usize = std::mem::size_of::<CtxCacheTbl>();
pub const CTX_ENCODE_CACHE_BYTES: usize = std::mem::size_of::<CtxEncodeCache>();
pub const CTX_DECODE_CACHE_BYTES: usize = std::mem::size_of::<CtxDecodeCache>();
impl Context {
// Encode a context into the global context data, or return
@ -892,7 +899,7 @@ impl Context {
return 0;
}
if let Some(idx) = Self::cache_get(self) {
if let Some(idx) = Self::encode_cache_get(self) {
incr_counter!(context_cache_hits);
debug_assert!(Self::decode(idx) == *self);
return idx;
@ -910,7 +917,8 @@ impl Context {
let idx: u32 = idx.try_into().unwrap();
// Save this offset into the cache
Self::cache_set(self, idx);
Self::encode_cache_set(self, idx);
Self::decode_cache_set(self, idx);
// In debug mode, check that the round-trip decoding always matches
debug_assert!(Self::decode(idx) == *self);
@ -923,16 +931,21 @@ impl Context {
return Context::default();
};
if let Some(ctx) = Self::decode_cache_get(start_idx) {
return ctx;
}
let context_data = CodegenGlobals::get_context_data();
let ctx = Self::decode_from(context_data, start_idx as usize);
Self::cache_set(&ctx, start_idx);
Self::encode_cache_set(&ctx, start_idx);
Self::decode_cache_set(&ctx, start_idx);
ctx
}
// Store an entry in a cache of recently encoded/decoded contexts
fn cache_set(ctx: &Context, idx: u32)
// Store an entry in a cache of recently encoded/decoded contexts for encoding
fn encode_cache_set(ctx: &Context, idx: u32)
{
// Compute the hash for this context
let mut hasher = DefaultHasher::new();
@ -941,21 +954,38 @@ impl Context {
unsafe {
// Lazily initialize the context cache
if CTX_CACHE == None {
if CTX_ENCODE_CACHE == None {
// Here we use the vec syntax to avoid allocating the large table on the stack,
// as this can cause a stack overflow
let tbl = vec![(Context::default(), 0); CTX_CACHE_SIZE].into_boxed_slice().try_into().unwrap();
CTX_CACHE = Some(tbl);
let tbl = vec![(Context::default(), 0); CTX_ENCODE_CACHE_SIZE].into_boxed_slice().try_into().unwrap();
CTX_ENCODE_CACHE = Some(tbl);
}
// Write a cache entry for this context
let cache = CTX_CACHE.as_mut().unwrap();
cache[ctx_hash % CTX_CACHE_SIZE] = (*ctx, idx);
let cache = CTX_ENCODE_CACHE.as_mut().unwrap();
cache[ctx_hash % CTX_ENCODE_CACHE_SIZE] = (*ctx, idx);
}
}
// Lookup the context in a cache of recently encoded/decoded contexts
fn cache_get(ctx: &Context) -> Option<u32>
// Store an entry in a cache of recently encoded/decoded contexts for decoding
fn decode_cache_set(ctx: &Context, idx: u32) {
unsafe {
// Lazily initialize the context cache
if CTX_DECODE_CACHE == None {
// Here we use the vec syntax to avoid allocating the large table on the stack,
// as this can cause a stack overflow
let tbl = vec![(Context::default(), 0); CTX_ENCODE_CACHE_SIZE].into_boxed_slice().try_into().unwrap();
CTX_DECODE_CACHE = Some(tbl);
}
// Write a cache entry for this context
let cache = CTX_DECODE_CACHE.as_mut().unwrap();
cache[idx as usize % CTX_ENCODE_CACHE_SIZE] = (*ctx, idx);
}
}
// Lookup the context in a cache of recently encoded/decoded contexts for encoding
fn encode_cache_get(ctx: &Context) -> Option<u32>
{
// Compute the hash for this context
let mut hasher = DefaultHasher::new();
@ -963,14 +993,14 @@ impl Context {
let ctx_hash = hasher.finish() as usize;
unsafe {
if CTX_CACHE == None {
if CTX_ENCODE_CACHE == None {
return None;
}
let cache = CTX_CACHE.as_mut().unwrap();
let cache = CTX_ENCODE_CACHE.as_mut().unwrap();
// Check that the context for this cache entry matches
let cache_entry = &cache[ctx_hash % CTX_CACHE_SIZE];
let cache_entry = &cache[ctx_hash % CTX_ENCODE_CACHE_SIZE];
if cache_entry.0 == *ctx {
debug_assert!(cache_entry.1 != 0);
return Some(cache_entry.1);
@ -980,6 +1010,25 @@ impl Context {
}
}
// Lookup the context in a cache of recently encoded/decoded contexts for decoding
fn decode_cache_get(start_idx: u32) -> Option<Context> {
unsafe {
if CTX_DECODE_CACHE == None {
return None;
}
let cache = CTX_DECODE_CACHE.as_mut().unwrap();
// Check that the start_idx for this cache entry matches
let cache_entry = &cache[start_idx as usize % CTX_DECODE_CACHE_SIZE];
if cache_entry.1 == start_idx {
return Some(cache_entry.0);
}
return None;
}
}
// Encode into a compressed context representation in a bit vector
fn encode_into(&self, bits: &mut BitVector) -> usize {
let start_idx = bits.num_bits();

2
yjit/src/stats.rs
View file

@ -775,7 +775,7 @@ fn rb_yjit_gen_stats_dict(key: VALUE) -> VALUE {
// How many bytes we are using to store context data
let context_data = CodegenGlobals::get_context_data();
set_stat_usize!(hash, "context_data_bytes", context_data.num_bytes());
set_stat_usize!(hash, "context_cache_bytes", crate::core::CTX_CACHE_BYTES);
set_stat_usize!(hash, "context_cache_bytes", crate::core::CTX_ENCODE_CACHE_BYTES + crate::core::CTX_DECODE_CACHE_BYTES);
// VM instructions count
set_stat_usize!(hash, "vm_insns_count", rb_vm_insns_count as usize);