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-rtc | 91 +++++++++++++++++++++++++++++++ 1 file changed, 91 insertions(+) create mode 100644 Documentation/ABI/testing/sysfs-class-rtc (limited to 'Documentation/ABI/testing/sysfs-class-rtc') diff --git a/Documentation/ABI/testing/sysfs-class-rtc b/Documentation/ABI/testing/sysfs-class-rtc new file mode 100644 index 000000000..95984289a --- /dev/null +++ b/Documentation/ABI/testing/sysfs-class-rtc @@ -0,0 +1,91 @@ +What: /sys/class/rtc/ +Date: March 2006 +KernelVersion: 2.6.17 +Contact: linux-rtc@vger.kernel.org +Description: + The rtc/ class subdirectory belongs to the RTC subsystem. + +What: /sys/class/rtc/rtcX/ +Date: March 2006 +KernelVersion: 2.6.17 +Contact: linux-rtc@vger.kernel.org +Description: + The /sys/class/rtc/rtc{0,1,2,3,...} directories correspond + to each RTC device. + +What: /sys/class/rtc/rtcX/date +Date: March 2006 +KernelVersion: 2.6.17 +Contact: linux-rtc@vger.kernel.org +Description: + (RO) RTC-provided date in YYYY-MM-DD format + +What: /sys/class/rtc/rtcX/hctosys +Date: September 2009 +KernelVersion: 2.6.32 +Contact: linux-rtc@vger.kernel.org +Description: + (RO) 1 if the RTC provided the system time at boot via the + CONFIG_RTC_HCTOSYS kernel option, 0 otherwise + +What: /sys/class/rtc/rtcX/max_user_freq +Date: October 2007 +KernelVersion: 2.6.24 +Contact: linux-rtc@vger.kernel.org +Description: + (RW) The maximum interrupt rate an unprivileged user may request + from this RTC. + +What: /sys/class/rtc/rtcX/name +Date: March 2006 +KernelVersion: 2.6.17 +Contact: linux-rtc@vger.kernel.org +Description: + (RO) The name of the RTC corresponding to this sysfs directory + +What: /sys/class/rtc/rtcX/range +Date: January 2018 +KernelVersion: 4.16 +Contact: linux-rtc@vger.kernel.org +Description: + Valid time range for the RTC, as seconds from epoch, formatted + as [min, max] + +What: /sys/class/rtc/rtcX/since_epoch +Date: March 2006 +KernelVersion: 2.6.17 +Contact: linux-rtc@vger.kernel.org +Description: + (RO) RTC-provided time as the number of seconds since the epoch + +What: /sys/class/rtc/rtcX/time +Date: March 2006 +KernelVersion: 2.6.17 +Contact: linux-rtc@vger.kernel.org +Description: + (RO) RTC-provided time in 24-hour notation (hh:mm:ss) + +What: /sys/class/rtc/rtcX/offset +Date: February 2016 +KernelVersion: 4.6 +Contact: linux-rtc@vger.kernel.org +Description: + (RW) The amount which the rtc clock has been adjusted in + firmware. Visible only if the driver supports clock offset + adjustment. The unit is parts per billion, i.e. The number of + clock ticks which are added to or removed from the rtc's base + clock per billion ticks. A positive value makes a day pass more + slowly, longer, and a negative value makes a day pass more + quickly. + +What: /sys/class/rtc/rtcX/wakealarm +Date: February 2007 +KernelVersion: 2.6.20 +Contact: linux-rtc@vger.kernel.org +Description: + (RW) The time at which the clock will generate a system wakeup + event. This is a one shot wakeup event, so must be reset after + wake if a daily wakeup is required. Format is seconds since the + epoch by default, or if there's a leading +, seconds in the + future, or if there is a leading +=, seconds ahead of the + current alarm. -- cgit v1.3.1