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/ldm.rst | 121 ++++++++++++++++++++++++++++++++++++++ 1 file changed, 121 insertions(+) create mode 100644 Documentation/admin-guide/ldm.rst (limited to 'Documentation/admin-guide/ldm.rst') diff --git a/Documentation/admin-guide/ldm.rst b/Documentation/admin-guide/ldm.rst new file mode 100644 index 000000000..12c571368 --- /dev/null +++ b/Documentation/admin-guide/ldm.rst @@ -0,0 +1,121 @@ +========================================== +LDM - Logical Disk Manager (Dynamic Disks) +========================================== + +:Author: Originally Written by FlatCap - Richard Russon . +:Last Updated: Anton Altaparmakov on 30 March 2007 for Windows Vista. + +Overview +-------- + +Windows 2000, XP, and Vista use a new partitioning scheme. It is a complete +replacement for the MSDOS style partitions. It stores its information in a +1MiB journalled database at the end of the physical disk. The size of +partitions is limited only by disk space. The maximum number of partitions is +nearly 2000. + +Any partitions created under the LDM are called "Dynamic Disks". There are no +longer any primary or extended partitions. Normal MSDOS style partitions are +now known as Basic Disks. + +If you wish to use Spanned, Striped, Mirrored or RAID 5 Volumes, you must use +Dynamic Disks. The journalling allows Windows to make changes to these +partitions and filesystems without the need to reboot. + +Once the LDM driver has divided up the disk, you can use the MD driver to +assemble any multi-partition volumes, e.g. Stripes, RAID5. + +To prevent legacy applications from repartitioning the disk, the LDM creates a +dummy MSDOS partition containing one disk-sized partition. This is what is +supported with the Linux LDM driver. + +A newer approach that has been implemented with Vista is to put LDM on top of a +GPT label disk. This is not supported by the Linux LDM driver yet. + + +Example +------- + +Below we have a 50MiB disk, divided into seven partitions. + +.. note:: + + The missing 1MiB at the end of the disk is where the LDM database is + stored. + ++-------++--------------+---------+-----++--------------+---------+----+ +|Device || Offset Bytes | Sectors | MiB || Size Bytes | Sectors | MiB| ++=======++==============+=========+=====++==============+=========+====+ +|hda || 0 | 0 | 0 || 52428800 | 102400 | 50| ++-------++--------------+---------+-----++--------------+---------+----+ +|hda1 || 51380224 | 100352 | 49 || 1048576 | 2048 | 1| ++-------++--------------+---------+-----++--------------+---------+----+ +|hda2 || 16384 | 32 | 0 || 6979584 | 13632 | 6| ++-------++--------------+---------+-----++--------------+---------+----+ +|hda3 || 6995968 | 13664 | 6 || 10485760 | 20480 | 10| ++-------++--------------+---------+-----++--------------+---------+----+ +|hda4 || 17481728 | 34144 | 16 || 4194304 | 8192 | 4| ++-------++--------------+---------+-----++--------------+---------+----+ +|hda5 || 21676032 | 42336 | 20 || 5242880 | 10240 | 5| ++-------++--------------+---------+-----++--------------+---------+----+ +|hda6 || 26918912 | 52576 | 25 || 10485760 | 20480 | 10| ++-------++--------------+---------+-----++--------------+---------+----+ +|hda7 || 37404672 | 73056 | 35 || 13959168 | 27264 | 13| ++-------++--------------+---------+-----++--------------+---------+----+ + +The LDM Database may not store the partitions in the order that they appear on +disk, but the driver will sort them. + +When Linux boots, you will see something like:: + + hda: 102400 sectors w/32KiB Cache, CHS=50/64/32 + hda: [LDM] hda1 hda2 hda3 hda4 hda5 hda6 hda7 + + +Compiling LDM Support +--------------------- + +To enable LDM, choose the following two options: + + - "Advanced partition selection" CONFIG_PARTITION_ADVANCED + - "Windows Logical Disk Manager (Dynamic Disk) support" CONFIG_LDM_PARTITION + +If you believe the driver isn't working as it should, you can enable the extra +debugging code. This will produce a LOT of output. The option is: + + - "Windows LDM extra logging" CONFIG_LDM_DEBUG + +N.B. The partition code cannot be compiled as a module. + +As with all the partition code, if the driver doesn't see signs of its type of +partition, it will pass control to another driver, so there is no harm in +enabling it. + +If you have Dynamic Disks but don't enable the driver, then all you will see +is a dummy MSDOS partition filling the whole disk. You won't be able to mount +any of the volumes on the disk. + + +Booting +------- + +If you enable LDM support, then lilo is capable of booting from any of the +discovered partitions. However, grub does not understand the LDM partitioning +and cannot boot from a Dynamic Disk. + + +More Documentation +------------------ + +There is an Overview of the LDM together with complete Technical Documentation. +It is available for download. + + http://www.linux-ntfs.org/ + +If you have any LDM questions that aren't answered in the documentation, email +me. + +Cheers, + FlatCap - Richard Russon + ldm@flatcap.org + -- cgit v1.3.1