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 --- Documentation/ABI/testing/sysfs-class-powercap | 152 +++++++++++++++++++++++++ 1 file changed, 152 insertions(+) create mode 100644 Documentation/ABI/testing/sysfs-class-powercap (limited to 'Documentation/ABI/testing/sysfs-class-powercap') diff --git a/Documentation/ABI/testing/sysfs-class-powercap b/Documentation/ABI/testing/sysfs-class-powercap new file mode 100644 index 000000000..ca491ec4e --- /dev/null +++ b/Documentation/ABI/testing/sysfs-class-powercap @@ -0,0 +1,152 @@ +What: /sys/class/powercap/ +Date: September 2013 +KernelVersion: 3.13 +Contact: linux-pm@vger.kernel.org +Description: + The powercap/ class sub directory belongs to the power cap + subsystem. Refer to + Documentation/power/powercap/powercap.rst for details. + +What: /sys/class/powercap/ +Date: September 2013 +KernelVersion: 3.13 +Contact: linux-pm@vger.kernel.org +Description: + A is a unique name under /sys/class/powercap. + Here determines how the power is going to be + controlled. A can contain multiple power zones. + +What: /sys/class/powercap//enabled +Date: September 2013 +KernelVersion: 3.13 +Contact: linux-pm@vger.kernel.org +Description: + This allows to enable/disable power capping for a "control type". + This status affects every power zone using this "control_type. + +What: /sys/class/powercap// +Date: September 2013 +KernelVersion: 3.13 +Contact: linux-pm@vger.kernel.org +Description: + A power zone is a single or a collection of devices, which can + be independently monitored and controlled. A power zone sysfs + entry is qualified with the name of the . + E.g. intel-rapl:0:1:1. + +What: /sys/class/powercap/// +Date: September 2013 +KernelVersion: 3.13 +Contact: linux-pm@vger.kernel.org +Description: + Power zones may be organized in a hierarchy in which child + power zones provide monitoring and control for a subset of + devices under the parent. For example, if there is a parent + power zone for a whole CPU package, each CPU core in it can + be a child power zone. + +What: /sys/class/powercap/...//name +Date: September 2013 +KernelVersion: 3.13 +Contact: linux-pm@vger.kernel.org +Description: + Specifies the name of this power zone. + +What: /sys/class/powercap/...//energy_uj +Date: September 2013 +KernelVersion: 3.13 +Contact: linux-pm@vger.kernel.org +Description: + Current energy counter in micro-joules. Write "0" to reset. + If the counter can not be reset, then this attribute is + read-only. + +What: /sys/class/powercap/...//max_energy_range_uj +Date: September 2013 +KernelVersion: 3.13 +Contact: linux-pm@vger.kernel.org +Description: + Range of the above energy counter in micro-joules. + + +What: /sys/class/powercap/...//power_uw +Date: September 2013 +KernelVersion: 3.13 +Contact: linux-pm@vger.kernel.org +Description: + Current power in micro-watts. + +What: /sys/class/powercap/...//max_power_range_uw +Date: September 2013 +KernelVersion: 3.13 +Contact: linux-pm@vger.kernel.org +Description: + Range of the above power value in micro-watts. + +What: /sys/class/powercap/...//constraint_X_name +Date: September 2013 +KernelVersion: 3.13 +Contact: linux-pm@vger.kernel.org +Description: + Each power zone can define one or more constraints. Each + constraint can have an optional name. Here "X" can have values + from 0 to max integer. + +What: /sys/class/powercap/...//constraint_X_power_limit_uw +Date: September 2013 +KernelVersion: 3.13 +Contact: linux-pm@vger.kernel.org +Description: + Power limit in micro-watts should be applicable for + the time window specified by "constraint_X_time_window_us". + Here "X" can have values from 0 to max integer. + +What: /sys/class/powercap/...//constraint_X_time_window_us +Date: September 2013 +KernelVersion: 3.13 +Contact: linux-pm@vger.kernel.org +Description: + Time window in micro seconds. This is used along with + constraint_X_power_limit_uw to define a power constraint. + Here "X" can have values from 0 to max integer. + + +What: /sys/class/powercap//.../constraint_X_max_power_uw +Date: September 2013 +KernelVersion: 3.13 +Contact: linux-pm@vger.kernel.org +Description: + Maximum allowed power in micro watts for this constraint. + Here "X" can have values from 0 to max integer. + +What: /sys/class/powercap//.../constraint_X_min_power_uw +Date: September 2013 +KernelVersion: 3.13 +Contact: linux-pm@vger.kernel.org +Description: + Minimum allowed power in micro watts for this constraint. + Here "X" can have values from 0 to max integer. + +What: /sys/class/powercap/...//constraint_X_max_time_window_us +Date: September 2013 +KernelVersion: 3.13 +Contact: linux-pm@vger.kernel.org +Description: + Maximum allowed time window in micro seconds for this + constraint. Here "X" can have values from 0 to max integer. + +What: /sys/class/powercap/...//constraint_X_min_time_window_us +Date: September 2013 +KernelVersion: 3.13 +Contact: linux-pm@vger.kernel.org +Description: + Minimum allowed time window in micro seconds for this + constraint. Here "X" can have values from 0 to max integer. + +What: /sys/class/powercap/...//enabled +Date: September 2013 +KernelVersion: 3.13 +Contact: linux-pm@vger.kernel.org +Description: + This allows to enable/disable power capping at power zone level. + This applies to current power zone and its children. -- cgit v1.3.1