Skip to content
Permalink
Browse files

Make the default parallelism 1

This changes the default parallelism for parallel compilers to one,
instead of the previous default, which was "num cpus". This is likely
not an optimal default long-term, but it is a good default for testing
whether parallel compilers are not a significant regression over a
sequential compiler.

Notably, this in theory makes a parallel-enabled compiler behave
exactly like a sequential compiler with respect to the jobserver.
  • Loading branch information...
Mark-Simulacrum committed Sep 30, 2019
1 parent a3639c6 commit 1a1067d1a537d6495f6aa9703e10119f05d578ad
@@ -813,6 +813,7 @@ macro_rules! options {
pub const parse_list: Option<&str> = Some("a space-separated list of strings");
pub const parse_opt_list: Option<&str> = Some("a space-separated list of strings");
pub const parse_opt_comma_list: Option<&str> = Some("a comma-separated list of strings");
pub const parse_threads: Option<&str> = Some("a number");
pub const parse_uint: Option<&str> = Some("a number");
pub const parse_passes: Option<&str> =
Some("a space-separated list of passes, or `all`");
@@ -956,6 +957,14 @@ macro_rules! options {
}
}

fn parse_threads(slot: &mut usize, v: Option<&str>) -> bool {
match v.and_then(|s| s.parse().ok()) {
Some(0) => { *slot = ::num_cpus::get(); true },
Some(i) => { *slot = i; true },
None => false
}
}

fn parse_uint(slot: &mut usize, v: Option<&str>) -> bool {
match v.and_then(|s| s.parse().ok()) {
Some(i) => { *slot = i; true },
@@ -1259,7 +1268,11 @@ options! {DebuggingOptions, DebuggingSetter, basic_debugging_options,
"prints the LLVM optimization passes being run"),
ast_json: bool = (false, parse_bool, [UNTRACKED],
"print the AST as JSON and halt"),
threads: Option<usize> = (None, parse_opt_uint, [UNTRACKED],
// We default to 1 here since we want to behave like
// a sequential compiler for now. This'll likely be adjusted
// in the future. Note that -Zthreads=0 is the way to get
// the num_cpus behavior.
threads: usize = (1, parse_threads, [UNTRACKED],
"use a thread pool with N threads"),
ast_json_noexpand: bool = (false, parse_bool, [UNTRACKED],
"print the pre-expansion AST as JSON and halt"),
@@ -2160,14 +2173,14 @@ pub fn build_session_options_and_crate_config(
}
}

if debugging_opts.threads == Some(0) {
if debugging_opts.threads == 0 {
early_error(
error_format,
"value for threads must be a positive non-zero integer",
);
}

if debugging_opts.threads.unwrap_or(1) > 1 && debugging_opts.fuel.is_some() {
if debugging_opts.threads > 1 && debugging_opts.fuel.is_some() {
early_error(
error_format,
"optimization fuel is incompatible with multiple threads",
@@ -897,16 +897,10 @@ impl Session {
ret
}

/// Returns the number of query threads that should be used for this
/// compilation
pub fn threads_from_count(query_threads: Option<usize>) -> usize {
query_threads.unwrap_or(::num_cpus::get())
}

/// Returns the number of query threads that should be used for this
/// compilation
pub fn threads(&self) -> usize {
Self::threads_from_count(self.opts.debugging_opts.threads)
self.opts.debugging_opts.threads
}

/// Returns the number of codegen units that should be used for this
@@ -147,5 +147,8 @@ where
F: FnOnce() -> R + Send,
R: Send,
{
util::spawn_thread_pool(edition, None, &None, f)
// the 1 here is duplicating code in config.opts.debugging_opts.threads
// which also defaults to 1; it ultimately doesn't matter as the default
// isn't threaded, and just ignores this parameter
util::spawn_thread_pool(edition, 1, &None, f)
}
@@ -173,7 +173,7 @@ pub fn scoped_thread<F: FnOnce() -> R + Send, R: Send>(cfg: thread::Builder, f:
#[cfg(not(parallel_compiler))]
pub fn spawn_thread_pool<F: FnOnce() -> R + Send, R: Send>(
edition: Edition,
_threads: Option<usize>,
_threads: usize,
stderr: &Option<Arc<Mutex<Vec<u8>>>>,
f: F,
) -> R {
@@ -198,7 +198,7 @@ pub fn spawn_thread_pool<F: FnOnce() -> R + Send, R: Send>(
#[cfg(parallel_compiler)]
pub fn spawn_thread_pool<F: FnOnce() -> R + Send, R: Send>(
edition: Edition,
threads: Option<usize>,
threads: usize,
stderr: &Option<Arc<Mutex<Vec<u8>>>>,
f: F,
) -> R {
@@ -209,7 +209,7 @@ pub fn spawn_thread_pool<F: FnOnce() -> R + Send, R: Send>(
let mut config = ThreadPoolBuilder::new()
.acquire_thread_handler(jobserver::acquire_thread)
.release_thread_handler(jobserver::release_thread)
.num_threads(Session::threads_from_count(threads))
.num_threads(threads)
.deadlock_handler(|| unsafe { ty::query::handle_deadlock() });

if let Some(size) = get_stack_size() {

0 comments on commit 1a1067d

Please sign in to comment.
You can’t perform that action at this time.