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-pps | 73 +++++++++++++++++++++++++++++++++++++ 1 file changed, 73 insertions(+) create mode 100644 Documentation/ABI/testing/sysfs-pps (limited to 'Documentation/ABI/testing/sysfs-pps') diff --git a/Documentation/ABI/testing/sysfs-pps b/Documentation/ABI/testing/sysfs-pps new file mode 100644 index 000000000..25028c7bc --- /dev/null +++ b/Documentation/ABI/testing/sysfs-pps @@ -0,0 +1,73 @@ +What: /sys/class/pps/ +Date: February 2008 +Contact: Rodolfo Giometti +Description: + The /sys/class/pps/ directory will contain files and + directories that will provide a unified interface to + the PPS sources. + +What: /sys/class/pps/ppsX/ +Date: February 2008 +Contact: Rodolfo Giometti +Description: + The /sys/class/pps/ppsX/ directory is related to X-th + PPS source into the system. Each directory will + contain files to manage and control its PPS source. + +What: /sys/class/pps/ppsX/assert +Date: February 2008 +Contact: Rodolfo Giometti +Description: + The /sys/class/pps/ppsX/assert file reports the assert events + and the assert sequence number of the X-th source in the form: + + .# + + If the source has no assert events the content of this file + is empty. + +What: /sys/class/pps/ppsX/clear +Date: February 2008 +Contact: Rodolfo Giometti +Description: + The /sys/class/pps/ppsX/clear file reports the clear events + and the clear sequence number of the X-th source in the form: + + .# + + If the source has no clear events the content of this file + is empty. + +What: /sys/class/pps/ppsX/mode +Date: February 2008 +Contact: Rodolfo Giometti +Description: + The /sys/class/pps/ppsX/mode file reports the functioning + mode of the X-th source in hexadecimal encoding. + + Please, refer to linux/include/linux/pps.h for further + info. + +What: /sys/class/pps/ppsX/echo +Date: February 2008 +Contact: Rodolfo Giometti +Description: + The /sys/class/pps/ppsX/echo file reports if the X-th does + or does not support an "echo" function. + +What: /sys/class/pps/ppsX/name +Date: February 2008 +Contact: Rodolfo Giometti +Description: + The /sys/class/pps/ppsX/name file reports the name of the + X-th source. + +What: /sys/class/pps/ppsX/path +Date: February 2008 +Contact: Rodolfo Giometti +Description: + The /sys/class/pps/ppsX/path file reports the path name of + the device connected with the X-th source. + + If the source is not connected with any device the content + of this file is empty. -- cgit v1.3.1