From 0d6526f82c3cdefcca47f73f5fc08dc6f335eac6 Mon Sep 17 00:00:00 2001 From: Tim Chen Date: Mon, 21 Sep 2026 17:37:22 -0700 Subject: sched/cache: Keep nr_pref_llc_running in the runnable domain, to fix LLC mis-scheduling bug alb_break_llc() decides whether to break LLC preference during active load balance. It does so by testing that every runnable fair task on the source rq prefers its LLC: env->src_rq->nr_pref_llc_running == env->src_rq->cfs.h_nr_runnable But the two counters cover different sets. nr_pref_llc_running is updated in account_llc_enqueue()/account_llc_dequeue(), next to cfs_rq->nr_queued, so it follows queued tasks. h_nr_runnable is updated in set_delayed()/ clear_delayed() and drops delay-dequeued tasks. So under DELAY_DEQUEUE, a preferring task that goes to sleep stays counted in nr_pref_llc_running while h_nr_runnable falls. The equality then breaks, alb_break_llc() returns false, and active balance is free to pull a task off its preferred LLC. Active balance only moves runnable tasks, and this is the only LLC check it consults: once the stopper runs, LBF_ACTIVE_LB skips the per-task test in can_migrate_task(). The runnable set is the one we want. Fix it on the counter side. A task should be counted in nr_pref_llc_running exactly while it is both queued on its preferred LLC (pref_llc_queued) and runnable (!sched_delayed). Define that membership once in task_pref_llc_runnable(), and adjust the counter only through pref_llc_running_inc()/pref_llc_running_dec() from the four sites that change either input: account_llc_enqueue(), account_llc_dequeue(), set_delayed() and clear_delayed(). Gating every update on the same predicate keeps the delay, wake and dequeue paths from double-counting or underflowing; see the comments at those sites for the ordering. nr_llc_running and sd->llc_counts are not touched and stay on queued semantics. Fixes: 714059f79ff0 ("sched/cache: Handle moving single tasks to/from their preferred LLC") Closes: https://lore.kernel.org/lkml/20260827135000.735138-1-zhanxusheng@xiaomi.com/ Reported-by: Zhan Xusheng Suggested-by: Chen Yu Signed-off-by: Tim Chen Signed-off-by: Peter Zijlstra (Intel) Signed-off-by: Ingo Molnar Reviewed-by: Kayra Cizmeci Cc: # v7.2.x Link: https://patch.msgid.link/06af61afedac32e6477f57feb4d658f6c411c3af.1790035273.git.tim.c.chen@linux.intel.com --- rust/syn/file.rs | 127 +++++++++++++++++++++++++++++++++++++++++++++++++++++++ 1 file changed, 127 insertions(+) create mode 100644 rust/syn/file.rs (limited to 'rust/syn/file.rs') diff --git a/rust/syn/file.rs b/rust/syn/file.rs new file mode 100644 index 000000000..ce2d2680c --- /dev/null +++ b/rust/syn/file.rs @@ -0,0 +1,127 @@ +// SPDX-License-Identifier: Apache-2.0 OR MIT + +use crate::attr::Attribute; +use crate::item::Item; + +ast_struct! { + /// A complete file of Rust source code. + /// + /// Typically `File` objects are created with [`parse_file`]. + /// + /// [`parse_file`]: crate::parse_file + /// + /// # Example + /// + /// Parse a Rust source file into a `syn::File` and print out a debug + /// representation of the syntax tree. + /// + /// ``` + /// use std::env; + /// use std::fs; + /// use std::process; + /// + /// fn main() { + /// # } + /// # + /// # fn fake_main() { + /// let mut args = env::args(); + /// let _ = args.next(); // executable name + /// + /// let filename = match (args.next(), args.next()) { + /// (Some(filename), None) => filename, + /// _ => { + /// eprintln!("Usage: dump-syntax path/to/filename.rs"); + /// process::exit(1); + /// } + /// }; + /// + /// let src = fs::read_to_string(&filename).expect("unable to read file"); + /// let syntax = syn::parse_file(&src).expect("unable to parse file"); + /// + /// // Debug impl is available if Syn is built with "extra-traits" feature. + /// println!("{:#?}", syntax); + /// } + /// ``` + /// + /// Running with its own source code as input, this program prints output + /// that begins with: + /// + /// ```text + /// File { + /// shebang: None, + /// attrs: [], + /// items: [ + /// Use( + /// ItemUse { + /// attrs: [], + /// vis: Inherited, + /// use_token: Use, + /// leading_colon: None, + /// tree: Path( + /// UsePath { + /// ident: Ident( + /// std, + /// ), + /// colon2_token: Colon2, + /// tree: Name( + /// UseName { + /// ident: Ident( + /// env, + /// ), + /// }, + /// ), + /// }, + /// ), + /// semi_token: Semi, + /// }, + /// ), + /// ... + /// ``` + #[cfg_attr(docsrs, doc(cfg(feature = "full")))] + pub struct File { + pub shebang: Option, + pub attrs: Vec, + pub items: Vec, + } +} + +#[cfg(feature = "parsing")] +pub(crate) mod parsing { + use crate::attr::Attribute; + use crate::error::Result; + use crate::file::File; + use crate::parse::{Parse, ParseStream}; + + #[cfg_attr(docsrs, doc(cfg(feature = "parsing")))] + impl Parse for File { + fn parse(input: ParseStream) -> Result { + Ok(File { + shebang: None, + attrs: input.call(Attribute::parse_inner)?, + items: { + let mut items = Vec::new(); + while !input.is_empty() { + items.push(input.parse()?); + } + items + }, + }) + } + } +} + +#[cfg(feature = "printing")] +mod printing { + use crate::attr::FilterAttrs; + use crate::file::File; + use proc_macro2::TokenStream; + use quote::{ToTokens, TokenStreamExt}; + + #[cfg_attr(docsrs, doc(cfg(feature = "printing")))] + impl ToTokens for File { + fn to_tokens(&self, tokens: &mut TokenStream) { + tokens.append_all(self.attrs.inner()); + tokens.append_all(&self.items); + } + } +} -- cgit v1.3.1