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/rtc-cdev | 50 ++++++++++++++++++++++++++++++++++++++ 1 file changed, 50 insertions(+) create mode 100644 Documentation/ABI/testing/rtc-cdev (limited to 'Documentation/ABI/testing/rtc-cdev') diff --git a/Documentation/ABI/testing/rtc-cdev b/Documentation/ABI/testing/rtc-cdev new file mode 100644 index 000000000..cec099a27 --- /dev/null +++ b/Documentation/ABI/testing/rtc-cdev @@ -0,0 +1,50 @@ +What: /dev/rtcX +Date: April 2005 +KernelVersion: 2.6.12 +Contact: linux-rtc@vger.kernel.org +Description: + The ioctl interface to drivers for real-time clocks (RTCs). + Following actions are supported: + + * RTC_RD_TIME, RTC_SET_TIME: Read or set the RTC time. Time + format is a Gregorian calendar date and 24 hour wall clock + time. + + * RTC_AIE_ON, RTC_AIE_OFF: Enable or disable the alarm interrupt + for RTCs that support alarms + + * RTC_ALM_READ, RTC_ALM_SET: Read or set the alarm time for + RTCs that support alarms. Can be set up to 24 hours in the + future. Requires a separate RTC_AIE_ON call to enable the + alarm interrupt. (Prefer to use RTC_WKALM_*) + + * RTC_WKALM_RD, RTC_WKALM_SET: For RTCs that support a more + powerful interface, which can issue alarms beyond 24 hours and + enable IRQs in the same request. + + * RTC_PIE_ON, RTC_PIE_OFF: Enable or disable the periodic + interrupt for RTCs that support periodic interrupts. + + * RTC_UIE_ON, RTC_UIE_OFF: Enable or disable the update + interrupt for RTCs that support it. + + * RTC_IRQP_READ, RTC_IRQP_SET: Read or set the frequency for + periodic interrupts for RTCs that support periodic interrupts. + Requires a separate RTC_PIE_ON call to enable the periodic + interrupts. + + * RTC_VL_READ: Read the voltage inputs status of the RTC when + supported. The value is a bit field of RTC_VL_*, giving the + status of the main and backup voltages. + + * RTC_VL_CLEAR: Clear the voltage status of the RTC. Some RTCs + need user interaction when the backup power provider is + replaced or charged to be able to clear the status. + + The ioctl() calls supported by the older /dev/rtc interface are + also supported by the newer RTC class framework. However, + because the chips and systems are not standardized, some PC/AT + functionality might not be provided. And in the same way, some + newer features -- including those enabled by ACPI -- are exposed + by the RTC class framework, but can't be supported by the older + driver. -- cgit v1.3.1