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-ptp | 142 ++++++++++++++++++++++++++++++++++++ 1 file changed, 142 insertions(+) create mode 100644 Documentation/ABI/testing/sysfs-ptp (limited to 'Documentation/ABI/testing/sysfs-ptp') diff --git a/Documentation/ABI/testing/sysfs-ptp b/Documentation/ABI/testing/sysfs-ptp new file mode 100644 index 000000000..9c317ac7c --- /dev/null +++ b/Documentation/ABI/testing/sysfs-ptp @@ -0,0 +1,142 @@ +What: /sys/class/ptp/ +Date: September 2010 +Contact: Richard Cochran +Description: + This directory contains files and directories + providing a standardized interface to the ancillary + features of PTP hardware clocks. + +What: /sys/class/ptp/ptp/ +Date: September 2010 +Contact: Richard Cochran +Description: + This directory contains the attributes of the Nth PTP + hardware clock registered into the PTP class driver + subsystem. + +What: /sys/class/ptp/ptp/clock_name +Date: September 2010 +Contact: Richard Cochran +Description: + This file contains the name of the PTP hardware clock + as a human readable string. The purpose of this + attribute is to provide the user with a "friendly + name" and to help distinguish PHY based devices from + MAC based ones. The string does not necessarily have + to be any kind of unique id. + +What: /sys/class/ptp/ptp/max_adjustment +Date: September 2010 +Contact: Richard Cochran +Description: + This file contains the PTP hardware clock's maximum + frequency adjustment value (a positive integer) in + parts per billion. + +What: /sys/class/ptp/ptp/max_vclocks +Date: May 2021 +Contact: Yangbo Lu +Description: + This file contains the maximum number of ptp vclocks. + Write integer to re-configure it. + +What: /sys/class/ptp/ptp/n_alarms +Date: September 2010 +Contact: Richard Cochran +Description: + This file contains the number of periodic or one shot + alarms offer by the PTP hardware clock. + +What: /sys/class/ptp/ptp/n_external_timestamps +Date: September 2010 +Contact: Richard Cochran +Description: + This file contains the number of external timestamp + channels offered by the PTP hardware clock. + +What: /sys/class/ptp/ptp/n_periodic_outputs +Date: September 2010 +Contact: Richard Cochran +Description: + This file contains the number of programmable periodic + output channels offered by the PTP hardware clock. + +What: /sys/class/ptp/ptp/n_pins +Date: March 2014 +Contact: Richard Cochran +Description: + This file contains the number of programmable pins + offered by the PTP hardware clock. + +What: /sys/class/ptp/ptp/n_vclocks +Date: May 2021 +Contact: Yangbo Lu +Description: + This file contains the number of virtual PTP clocks in + use. By default, the value is 0 meaning that only the + physical clock is in use. Setting the value creates + the corresponding number of virtual clocks and causes + the physical clock to become free running. Setting the + value back to 0 deletes the virtual clocks and + switches the physical clock back to normal, adjustable + operation. + +What: /sys/class/ptp/ptp/pins +Date: March 2014 +Contact: Richard Cochran +Description: + This directory contains one file for each programmable + pin offered by the PTP hardware clock. The file name + is the hardware dependent pin name. Reading from this + file produces two numbers, the assigned function (see + the `PTP_PF_` enumeration values in linux/ptp_clock.h) + and the channel number. The function and channel + assignment may be changed by two writing numbers into + the file. + +What: /sys/class/ptp/ptp/pps_available +Date: September 2010 +Contact: Richard Cochran +Description: + This file indicates whether the PTP hardware clock + supports a Pulse Per Second to the host CPU. Reading + "1" means that the PPS is supported, while "0" means + not supported. + +What: /sys/class/ptp/ptp/extts_enable +Date: September 2010 +Contact: Richard Cochran +Description: + This write-only file enables or disables external + timestamps. To enable external timestamps, write the + channel index followed by a "1" into the file. + To disable external timestamps, write the channel + index followed by a "0" into the file. + +What: /sys/class/ptp/ptp/fifo +Date: September 2010 +Contact: Richard Cochran +Description: + This file provides timestamps on external events, in + the form of three integers: channel index, seconds, + and nanoseconds. + +What: /sys/class/ptp/ptp/period +Date: September 2010 +Contact: Richard Cochran +Description: + This write-only file enables or disables periodic + outputs. To enable a periodic output, write five + integers into the file: channel index, start time + seconds, start time nanoseconds, period seconds, and + period nanoseconds. To disable a periodic output, set + all the seconds and nanoseconds values to zero. + +What: /sys/class/ptp/ptp/pps_enable +Date: September 2010 +Contact: Richard Cochran +Description: + This write-only file enables or disables delivery of + PPS events to the Linux PPS subsystem. To enable PPS + events, write a "1" into the file. To disable events, + write a "0" into the file. -- cgit v1.3.1