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/admin-guide/sysctl/index.rst | 107 +++++++++++++++++++++++++++++ 1 file changed, 107 insertions(+) create mode 100644 Documentation/admin-guide/sysctl/index.rst (limited to 'Documentation/admin-guide/sysctl/index.rst') diff --git a/Documentation/admin-guide/sysctl/index.rst b/Documentation/admin-guide/sysctl/index.rst new file mode 100644 index 000000000..50f00514f --- /dev/null +++ b/Documentation/admin-guide/sysctl/index.rst @@ -0,0 +1,107 @@ +=========================== +Documentation for /proc/sys +=========================== + +Copyright (c) 1998, 1999, Rik van Riel + +------------------------------------------------------------------------------ + +'Why', I hear you ask, 'would anyone even _want_ documentation +for them sysctl files? If anybody really needs it, it's all in +the source...' + +Well, this documentation is written because some people either +don't know they need to tweak something, or because they don't +have the time or knowledge to read the source code. + +Furthermore, the programmers who built sysctl have built it to +be actually used, not just for the fun of programming it :-) + +------------------------------------------------------------------------------ + +Legal blurb: + +As usual, there are two main things to consider: + +1. you get what you pay for +2. it's free + +The consequences are that I won't guarantee the correctness of +this document, and if you come to me complaining about how you +screwed up your system because of wrong documentation, I won't +feel sorry for you. I might even laugh at you... + +But of course, if you _do_ manage to screw up your system using +only the sysctl options used in this file, I'd like to hear of +it. Not only to have a great laugh, but also to make sure that +you're the last RTFMing person to screw up. + +In short, e-mail your suggestions, corrections and / or horror +stories to: + +Rik van Riel. + +-------------------------------------------------------------- + +Introduction +============ + +Sysctl is a means of configuring certain aspects of the kernel +at run-time, and the /proc/sys/ directory is there so that you +don't even need special tools to do it! +In fact, there are only four things needed to use these config +facilities: + +- a running Linux system +- root access +- common sense (this is especially hard to come by these days) +- knowledge of what all those values mean + +As a quick 'ls /proc/sys' will show, the directory consists of +several (arch-dependent?) subdirs. Each subdir is mainly about +one part of the kernel, so you can do configuration on a piece +by piece basis, or just some 'thematic frobbing'. + +This documentation is about: + +=============== =============================================================== +abi/ execution domains & personalities +<$ARCH> tuning controls for various CPU architecture (e.g. csky, s390) +crypto/ cryptographic subsystem +debug/ debugging features +dev/ device specific information (e.g. dev/cdrom/info) +fs/ specific filesystems + filehandle, inode, dentry and quota tuning + binfmt_misc +kernel/ global kernel info / tuning + miscellaneous stuff + some architecture-specific controls + security (LSM) stuff +net/ networking stuff, for documentation look in: + +proc/ +sunrpc/ SUN Remote Procedure Call (NFS) +user/ Per user namespace limits +vm/ memory management tuning + buffer and cache management +xen/ Xen hypervisor controls +=============== =============================================================== + +These are the subdirs I have on my system or have been discovered by +searching through the source code. There might be more or other subdirs +in another setup. If you see another dir, I'd really like to hear about +it :-) + +.. toctree:: + :maxdepth: 1 + + abi + crypto + debug + fs + kernel + net + sunrpc + user + vm + xen -- cgit v1.3.1