Skip to content

gh-143158: Hot cold code splitting for JIT compiler #149292

New issue

Have a question about this project? Sign up for a free GitHub account to open an issue and contact its maintainers and the community.

Sign up for GitHub

By clicking “Sign up for GitHub”, you agree to our terms of service and privacy statement. We’ll occasionally send you account related emails.

Already on GitHub? Sign in to your account

Draft
waterlens wants to merge 2 commits into
base: main
Choose a base branch
from
Draft

gh-143158: Hot cold code splitting for JIT compiler #149292

Show file tree
Hide file tree
Changes from all commits
Commits
Show all changes
2 commits
Select commit Hold shift + click to select a range
a509e18
Move cold code after _JIT_CONTINUE
waterlens Apr 25, 2026
c180cc0
Split JIT stencils into hot and cold code
waterlens May 11, 2026
File filter

Filter by extension

Filter by extension
Conversations
Failed to load comments.
Loading
Jump to
Jump to file
Failed to load files.
Loading
Diff view
Diff view
26 changes: 17 additions & 9 deletions Python/jit.c
View file
Open in desktop
Original file line number Diff line number Diff line change
Expand Up @@ -645,20 +645,23 @@ _PyJIT_Compile(_PyExecutorObject *executor, const _PyUOpInstruction trace[], siz
{
const StencilGroup *group;
// Loop once to find the total compiled size:
size_t code_size = 0;
size_t hot_code_size = 0;
size_t cold_code_size = 0;
size_t data_size = 0;
jit_state state = {0};
for (size_t i = 0; i < length; i++) {
const _PyUOpInstruction *instruction = &trace[i];
group = &stencil_groups[instruction->opcode];
state.instruction_starts[i] = code_size;
code_size += group->code_size;
state.instruction_starts[i] = hot_code_size;
hot_code_size += group->hot_code_size;
cold_code_size += group->cold_code_size;
data_size += group->data_size;
combine_symbol_mask(group->trampoline_mask, state.trampolines.mask);
combine_symbol_mask(group->got_mask, state.got_symbols.mask);
}
group = &stencil_groups[_FATAL_ERROR_r00];
code_size += group->code_size;
hot_code_size += group->hot_code_size;
cold_code_size += group->cold_code_size;
data_size += group->data_size;
combine_symbol_mask(group->trampoline_mask, state.trampolines.mask);
combine_symbol_mask(group->got_mask, state.got_symbols.mask);
Expand All @@ -672,6 +675,7 @@ _PyJIT_Compile(_PyExecutorObject *executor, const _PyUOpInstruction trace[], siz
// Round up to the nearest page:
size_t page_size = get_page_size();
assert((page_size & (page_size - 1)) == 0);
size_t code_size = hot_code_size + cold_code_size;
size_t code_padding = DATA_ALIGN - ((code_size + state.trampolines.size) & (DATA_ALIGN - 1));
size_t padding = page_size - ((code_size + state.trampolines.size + code_padding + data_size + state.got_symbols.size) & (page_size - 1));
size_t total_size = code_size + state.trampolines.size + code_padding + data_size + state.got_symbols.size + padding;
Expand All @@ -693,23 +697,27 @@ _PyJIT_Compile(_PyExecutorObject *executor, const _PyUOpInstruction trace[], siz
}
// Loop again to emit the code:
unsigned char *code = memory;
unsigned char *cold = memory + hot_code_size;
state.trampolines.mem = memory + code_size;
unsigned char *data = memory + code_size + state.trampolines.size + code_padding;
assert(trace[0].opcode == _START_EXECUTOR_r00 || trace[0].opcode == _COLD_EXIT_r00 || trace[0].opcode == _COLD_DYNAMIC_EXIT_r00);
state.got_symbols.mem = data + data_size;
for (size_t i = 0; i < length; i++) {
const _PyUOpInstruction *instruction = &trace[i];
group = &stencil_groups[instruction->opcode];
group->emit(code, data, executor, instruction, &state);
code += group->code_size;
group->emit(code, cold, data, executor, instruction, &state);
code += group->hot_code_size;
cold += group->cold_code_size;
data += group->data_size;
}
// Protect against accidental buffer overrun into data:
group = &stencil_groups[_FATAL_ERROR_r00];
group->emit(code, data, executor, NULL, &state);
code += group->code_size;
group->emit(code, cold, data, executor, NULL, &state);
code += group->hot_code_size;
cold += group->cold_code_size;
data += group->data_size;
assert(code == memory + code_size);
assert(code == memory + hot_code_size);
assert(cold == memory + code_size);
assert(data == memory + code_size + state.trampolines.size + code_padding + data_size);
if (mark_executable(memory, total_size)) {
jit_free(memory, total_size);
Expand Down
Loading
Loading