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/tt.rs | 109 +++++++++++++++++++++++++++++++++++++++++++++++++++++++++ 1 file changed, 109 insertions(+) create mode 100644 rust/syn/tt.rs (limited to 'rust/syn/tt.rs') diff --git a/rust/syn/tt.rs b/rust/syn/tt.rs new file mode 100644 index 000000000..fc7adec3d --- /dev/null +++ b/rust/syn/tt.rs @@ -0,0 +1,109 @@ +// SPDX-License-Identifier: Apache-2.0 OR MIT + +use proc_macro2::{Delimiter, TokenStream, TokenTree}; +use std::hash::{Hash, Hasher}; + +pub(crate) struct TokenTreeHelper<'a>(pub &'a TokenTree); + +impl<'a> PartialEq for TokenTreeHelper<'a> { + fn eq(&self, other: &Self) -> bool { + use proc_macro2::Spacing; + + match (self.0, other.0) { + (TokenTree::Group(g1), TokenTree::Group(g2)) => { + match (g1.delimiter(), g2.delimiter()) { + (Delimiter::Parenthesis, Delimiter::Parenthesis) + | (Delimiter::Brace, Delimiter::Brace) + | (Delimiter::Bracket, Delimiter::Bracket) + | (Delimiter::None, Delimiter::None) => {} + _ => return false, + } + + let s1 = g1.stream().into_iter(); + let mut s2 = g2.stream().into_iter(); + + for item1 in s1 { + let item2 = match s2.next() { + Some(item) => item, + None => return false, + }; + if TokenTreeHelper(&item1) != TokenTreeHelper(&item2) { + return false; + } + } + s2.next().is_none() + } + (TokenTree::Punct(o1), TokenTree::Punct(o2)) => { + o1.as_char() == o2.as_char() + && match (o1.spacing(), o2.spacing()) { + (Spacing::Alone, Spacing::Alone) | (Spacing::Joint, Spacing::Joint) => true, + _ => false, + } + } + (TokenTree::Literal(l1), TokenTree::Literal(l2)) => l1.to_string() == l2.to_string(), + (TokenTree::Ident(s1), TokenTree::Ident(s2)) => s1 == s2, + _ => false, + } + } +} + +impl<'a> Hash for TokenTreeHelper<'a> { + fn hash(&self, h: &mut H) { + use proc_macro2::Spacing; + + match self.0 { + TokenTree::Group(g) => { + 0u8.hash(h); + match g.delimiter() { + Delimiter::Parenthesis => 0u8.hash(h), + Delimiter::Brace => 1u8.hash(h), + Delimiter::Bracket => 2u8.hash(h), + Delimiter::None => 3u8.hash(h), + } + + for item in g.stream() { + TokenTreeHelper(&item).hash(h); + } + 0xFFu8.hash(h); // terminator w/ a variant we don't normally hash + } + TokenTree::Punct(op) => { + 1u8.hash(h); + op.as_char().hash(h); + match op.spacing() { + Spacing::Alone => 0u8.hash(h), + Spacing::Joint => 1u8.hash(h), + } + } + TokenTree::Literal(lit) => (2u8, lit.to_string()).hash(h), + TokenTree::Ident(word) => (3u8, word).hash(h), + } + } +} + +pub(crate) struct TokenStreamHelper<'a>(pub &'a TokenStream); + +impl<'a> PartialEq for TokenStreamHelper<'a> { + fn eq(&self, other: &Self) -> bool { + let left = self.0.clone().into_iter().collect::>(); + let right = other.0.clone().into_iter().collect::>(); + if left.len() != right.len() { + return false; + } + for (a, b) in left.into_iter().zip(right) { + if TokenTreeHelper(&a) != TokenTreeHelper(&b) { + return false; + } + } + true + } +} + +impl<'a> Hash for TokenStreamHelper<'a> { + fn hash(&self, state: &mut H) { + let tts = self.0.clone().into_iter().collect::>(); + tts.len().hash(state); + for tt in tts { + TokenTreeHelper(&tt).hash(state); + } + } +} -- cgit v1.3.1