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 --- samples/rust/rust_soc.rs | 78 ++++++++++++++++++++++++++++++++++++++++++++++++ 1 file changed, 78 insertions(+) create mode 100644 samples/rust/rust_soc.rs (limited to 'samples/rust/rust_soc.rs') diff --git a/samples/rust/rust_soc.rs b/samples/rust/rust_soc.rs new file mode 100644 index 000000000..f5e5f2f9a --- /dev/null +++ b/samples/rust/rust_soc.rs @@ -0,0 +1,78 @@ +// SPDX-License-Identifier: GPL-2.0 + +//! Rust SoC Platform driver sample. + +use kernel::{ + acpi, + device::Core, + of, + platform, + prelude::*, + soc, + str::CString, + sync::aref::ARef, // +}; +use pin_init::pin_init_scope; + +#[pin_data] +struct SampleSocDriver { + pdev: ARef, + #[pin] + _dev_reg: soc::Registration, +} + +kernel::of_device_table!( + OF_TABLE, + ::IdInfo, + [(of::DeviceId::new(c"test,rust-device"), ())] +); + +kernel::acpi_device_table!( + ACPI_TABLE, + ::IdInfo, + [(acpi::DeviceId::new(c"LNUXBEEF"), ())] +); + +impl platform::Driver for SampleSocDriver { + type IdInfo = (); + type Data<'bound> = Self; + const OF_ID_TABLE: Option> = Some(&OF_TABLE); + const ACPI_ID_TABLE: Option> = Some(&ACPI_TABLE); + + fn probe<'bound>( + pdev: &'bound platform::Device>, + _info: Option<&'bound Self::IdInfo>, + ) -> impl PinInit + 'bound { + dev_dbg!(pdev, "Probe Rust SoC driver sample.\n"); + + let pdev = pdev.into(); + pin_init_scope(move || { + let machine = CString::try_from(c"My cool ACME15 dev board")?; + let family = CString::try_from(c"ACME")?; + let revision = CString::try_from(c"1.2")?; + let serial_number = CString::try_from(c"12345")?; + let soc_id = CString::try_from(c"ACME15")?; + + let attr = soc::Attributes { + machine: Some(machine), + family: Some(family), + revision: Some(revision), + serial_number: Some(serial_number), + soc_id: Some(soc_id), + }; + + Ok(try_pin_init!(SampleSocDriver { + pdev: pdev, + _dev_reg <- soc::Registration::new(attr), + }? Error)) + }) + } +} + +kernel::module_platform_driver! { + type: SampleSocDriver, + name: "rust_soc", + authors: ["Matthew Maurer"], + description: "Rust SoC Driver", + license: "GPL", +} -- cgit v1.3.1