From 50c2c4bddee5a2c5edc0d9fc0f635befdfc4bacc Mon Sep 17 00:00:00 2001 From: Aaron Patterson Date: Thu, 9 Jan 2025 10:21:00 -0800 Subject: [PATCH] Make rb_vm_insns_count a thread local variable `rb_vm_insns_count` is a global variable used for reporting YJIT statistics. It is a counter that tallies the number of interpreter instructions that have been executed, this way we can approximate how much time we're spending in YJIT compared to the interpreter. Unfortunately keeping this statistic means that every instruction executed in the interpreter loop must increment the counter. Normally this isn't a problem, but in multi-threaded situations (when Ractors are used), incrementing this counter can become quite costly due to page caching issues. Additionally, since there is no locking when incrementing this global, the count can't really make sense in a multi-threaded environment. This commit changes `rb_vm_insns_count` to a thread local. That way each Ractor has it's own copy of the counter and incrementing the counter becomes quite cheap. Of course this means that in multi-threaded situations, the value doesn't really make sense (but it didn't make sense before because of the lack of locking). The counter is used for YJIT statistics, and since YJIT is basically disabled when Ractors are in use, I don't think we care about inaccuracies (for the time being). We can revisit this counter when we give YJIT multi-threading support, but for the time being this commit restores multi-threaded performance. To test this, I used the benchmark in [Bug #20489]. Here is the performance on Ruby 3.2: ``` $ time RUBY_MAX_CPU=12 ./miniruby -v ../test.rb 8 8 ruby 3.2.0 (2022-12-25 revision a528908271) [x86_64-linux] [0...1, 1...2, 2...3, 3...4, 4...5, 5...6, 6...7, 7...8] ../test.rb:43: warning: Ractor is experimental, and the behavior may change in future versions of Ruby! Also there are many implementation issues. ________________________________________________________ Executed in 2.53 secs fish external usr time 19.86 secs 370.00 micros 19.86 secs sys time 0.02 secs 320.00 micros 0.02 secs ``` We can see the regression in performance on the master branch: ``` $ time RUBY_MAX_CPU=12 ./miniruby -v ../test.rb 8 8 ruby 3.5.0dev (2025-01-10T16:22:26Z master 4a2702dafb) +PRISM [x86_64-linux] [0...1, 1...2, 2...3, 3...4, 4...5, 5...6, 6...7, 7...8] ../test.rb:43: warning: Ractor is experimental, and the behavior may change in future versions of Ruby! Also there are many implementation issues. ________________________________________________________ Executed in 24.87 secs fish external usr time 195.55 secs 0.00 micros 195.55 secs sys time 0.00 secs 716.00 micros 0.00 secs ``` Here are the stats after this commit: ``` $ time RUBY_MAX_CPU=12 ./miniruby -v ../test.rb 8 8 ruby 3.5.0dev (2025-01-10T20:37:06Z tl 3ef0432779) +PRISM [x86_64-linux] [0...1, 1...2, 2...3, 3...4, 4...5, 5...6, 6...7, 7...8] ../test.rb:43: warning: Ractor is experimental, and the behavior may change in future versions of Ruby! Also there are many implementation issues. ________________________________________________________ Executed in 2.46 secs fish external usr time 19.34 secs 381.00 micros 19.34 secs sys time 0.01 secs 321.00 micros 0.01 secs ``` [Bug #20489] --- internal/vm.h | 2 +- rjit.c | 2 +- rjit_c.c | 2 +- vm_exec.c | 2 +- yjit.c | 6 ++++++ yjit/bindgen/src/main.rs | 4 +--- yjit/src/cruby_bindings.inc.rs | 2 +- yjit/src/stats.rs | 4 ++-- 8 files changed, 14 insertions(+), 10 deletions(-) diff --git a/internal/vm.h b/internal/vm.h index c30e26a8b4..f8461ba6d6 100644 --- a/internal/vm.h +++ b/internal/vm.h @@ -81,7 +81,7 @@ struct vm_ifunc *rb_current_ifunc(void); #if USE_YJIT /* vm_exec.c */ -extern uint64_t rb_vm_insns_count; +extern RB_THREAD_LOCAL_SPECIFIER uint64_t rb_vm_insns_count; #endif extern bool rb_free_at_exit; diff --git a/rjit.c b/rjit.c index 72660394b3..4a01a12d77 100644 --- a/rjit.c +++ b/rjit.c @@ -170,7 +170,7 @@ struct rb_rjit_runtime_counters rb_rjit_counters = { 0 }; extern VALUE rb_gc_enable(void); extern VALUE rb_gc_disable(void); -extern uint64_t rb_vm_insns_count; +extern RB_THREAD_LOCAL_SPECIFIER uint64_t rb_vm_insns_count; // Disable GC, TracePoint, JIT, stats, and $! #define WITH_RJIT_ISOLATED_USING_PC(using_pc, stmt) do { \ diff --git a/rjit_c.c b/rjit_c.c index e421763480..fd09ac87c6 100644 --- a/rjit_c.c +++ b/rjit_c.c @@ -541,7 +541,7 @@ extern VALUE rb_vm_set_ivar_id(VALUE obj, ID id, VALUE val); extern VALUE rb_ary_unshift_m(int argc, VALUE *argv, VALUE ary); extern void* rb_rjit_entry_stub_hit(VALUE branch_stub); extern void* rb_rjit_branch_stub_hit(VALUE branch_stub, int sp_offset, int target0_p); -extern uint64_t rb_vm_insns_count; +extern RB_THREAD_LOCAL_SPECIFIER uint64_t rb_vm_insns_count; #include "rjit_c.rbinc" diff --git a/vm_exec.c b/vm_exec.c index 44d92e2225..2f5e572da9 100644 --- a/vm_exec.c +++ b/vm_exec.c @@ -13,7 +13,7 @@ #if USE_YJIT || USE_RJIT // The number of instructions executed on vm_exec_core. --yjit-stats uses this. -uint64_t rb_vm_insns_count = 0; +RB_THREAD_LOCAL_SPECIFIER uint64_t rb_vm_insns_count = 0; #endif #if VM_COLLECT_USAGE_DETAILS diff --git a/yjit.c b/yjit.c index 6a1d0308b2..39774252b3 100644 --- a/yjit.c +++ b/yjit.c @@ -16,6 +16,7 @@ #include "internal/fixnum.h" #include "internal/numeric.h" #include "internal/gc.h" +#include "internal/vm.h" #include "vm_core.h" #include "vm_callinfo.h" #include "builtin.h" @@ -96,6 +97,11 @@ rb_yjit_mark_executable(void *mem_block, uint32_t mem_size) } } +uint64_t +rb_yjit_vm_insns_count(void) { + return rb_vm_insns_count; +} + // Free the specified memory block. bool rb_yjit_mark_unused(void *mem_block, uint32_t mem_size) diff --git a/yjit/bindgen/src/main.rs b/yjit/bindgen/src/main.rs index e8f88cef64..b6f4c4b7c4 100644 --- a/yjit/bindgen/src/main.rs +++ b/yjit/bindgen/src/main.rs @@ -317,6 +317,7 @@ fn main() { .allowlist_function("rb_yjit_get_page_size") .allowlist_function("rb_yjit_iseq_builtin_attrs") .allowlist_function("rb_yjit_iseq_inspect") + .allowlist_function("rb_yjit_vm_insns_count") .allowlist_function("rb_yjit_builtin_function") .allowlist_function("rb_set_cfp_(pc|sp)") .allowlist_function("rb_yjit_multi_ractor_p") @@ -380,9 +381,6 @@ fn main() { .allowlist_function("rb_ivar_get") .allowlist_function("rb_mod_name") - // From internal/vm.h - .allowlist_var("rb_vm_insns_count") - // From include/ruby/internal/intern/vm.h .allowlist_function("rb_get_alloc_func") diff --git a/yjit/src/cruby_bindings.inc.rs b/yjit/src/cruby_bindings.inc.rs index d9bcd2634c..7ad24a274c 100644 --- a/yjit/src/cruby_bindings.inc.rs +++ b/yjit/src/cruby_bindings.inc.rs @@ -1061,7 +1061,6 @@ extern "C" { elts: *const VALUE, ) -> VALUE; pub fn rb_vm_top_self() -> VALUE; - pub static mut rb_vm_insns_count: u64; pub fn rb_method_entry_at(obj: VALUE, id: ID) -> *const rb_method_entry_t; pub fn rb_callable_method_entry(klass: VALUE, id: ID) -> *const rb_callable_method_entry_t; pub fn rb_callable_method_entry_or_negative( @@ -1141,6 +1140,7 @@ extern "C" { pub fn rb_jit_cont_each_iseq(callback: rb_iseq_callback, data: *mut ::std::os::raw::c_void); pub fn rb_yjit_mark_writable(mem_block: *mut ::std::os::raw::c_void, mem_size: u32) -> bool; pub fn rb_yjit_mark_executable(mem_block: *mut ::std::os::raw::c_void, mem_size: u32); + pub fn rb_yjit_vm_insns_count() -> u64; pub fn rb_yjit_mark_unused(mem_block: *mut ::std::os::raw::c_void, mem_size: u32) -> bool; pub fn rb_yjit_array_len(a: VALUE) -> ::std::os::raw::c_long; pub fn rb_yjit_icache_invalidate( diff --git a/yjit/src/stats.rs b/yjit/src/stats.rs index 3a3965577b..aa0b3d528c 100644 --- a/yjit/src/stats.rs +++ b/yjit/src/stats.rs @@ -792,7 +792,7 @@ fn rb_yjit_gen_stats_dict(key: VALUE) -> VALUE { 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); + set_stat_usize!(hash, "vm_insns_count", rb_yjit_vm_insns_count() as usize); set_stat_usize!(hash, "live_iseq_count", rb_yjit_live_iseq_count as usize); set_stat_usize!(hash, "iseq_alloc_count", rb_yjit_iseq_alloc_count as usize); @@ -862,7 +862,7 @@ fn rb_yjit_gen_stats_dict(key: VALUE) -> VALUE { set_stat_double!(hash, "avg_len_in_yjit", avg_len_in_yjit); // Proportion of instructions that retire in YJIT - let total_insns_count = retired_in_yjit + rb_vm_insns_count; + let total_insns_count = retired_in_yjit + rb_yjit_vm_insns_count(); set_stat_usize!(hash, "total_insns_count", total_insns_count as usize); let ratio_in_yjit: f64 = 100.0 * retired_in_yjit as f64 / total_insns_count as f64;