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-bus-vfio-mdev | 113 ++++++++++++++++++++++++++ 1 file changed, 113 insertions(+) create mode 100644 Documentation/ABI/testing/sysfs-bus-vfio-mdev (limited to 'Documentation/ABI/testing/sysfs-bus-vfio-mdev') diff --git a/Documentation/ABI/testing/sysfs-bus-vfio-mdev b/Documentation/ABI/testing/sysfs-bus-vfio-mdev new file mode 100644 index 000000000..59fc80426 --- /dev/null +++ b/Documentation/ABI/testing/sysfs-bus-vfio-mdev @@ -0,0 +1,113 @@ +What: /sys/...//mdev_supported_types/ +Date: October 2016 +Contact: Kirti Wankhede +Description: + This directory contains list of directories of currently + supported mediated device types and their details for + . Supported type attributes are defined by the + vendor driver who registers with Mediated device framework. + Each supported type is a directory whose name is created + by adding the device driver string as a prefix to the + string provided by the vendor driver. + +What: /sys/...//mdev_supported_types// +Date: October 2016 +Contact: Kirti Wankhede +Description: + This directory gives details of supported type, like name, + description, available_instances, device_api etc. + 'device_api' and 'available_instances' are mandatory + attributes to be provided by vendor driver. 'name', + 'description' and other vendor driver specific attributes + are optional. + +What: /sys/.../mdev_supported_types//create +Date: October 2016 +Contact: Kirti Wankhede +Description: + Writing UUID to this file will create mediated device of + type for parent device . This is a + write-only file. + For example:: + + # echo "83b8f4f2-509f-382f-3c1e-e6bfe0fa1001" > \ + /sys/devices/foo/mdev_supported_types/foo-1/create + +What: /sys/.../mdev_supported_types//devices/ +Date: October 2016 +Contact: Kirti Wankhede +Description: + This directory contains symbolic links pointing to mdev + devices sysfs entries which are created of this . + +What: /sys/.../mdev_supported_types//available_instances +Date: October 2016 +Contact: Kirti Wankhede +Description: + Reading this attribute will show the number of mediated + devices of type that can be created. This is a + readonly file. +Users: + Userspace applications interested in creating mediated + device of that type. Userspace application should check + the number of available instances could be created before + creating mediated device of this type. + +What: /sys/.../mdev_supported_types//device_api +Date: October 2016 +Contact: Kirti Wankhede +Description: + Reading this attribute will show VFIO device API supported + by this type. For example, "vfio-pci" for a PCI device, + "vfio-platform" for platform device. + +What: /sys/.../mdev_supported_types//name +Date: October 2016 +Contact: Kirti Wankhede +Description: + Reading this attribute will show human readable name of the + mediated device that will get created of type . + This is optional attribute. For example: "Grid M60-0Q" +Users: + Userspace applications interested in knowing the name of + a particular that can help in understanding the + type of mediated device. + +What: /sys/.../mdev_supported_types//description +Date: October 2016 +Contact: Kirti Wankhede +Description: + Reading this attribute will show description of the type of + mediated device that will get created of type . + This is optional attribute. For example: + "2 heads, 512M FB, 2560x1600 maximum resolution" +Users: + Userspace applications interested in knowing the details of + a particular that can help in understanding the + features provided by that type of mediated device. + +What: /sys/.../// +Date: October 2016 +Contact: Kirti Wankhede +Description: + This directory represents device directory of mediated + device. It contains all the attributes related to mediated + device. + +What: /sys/...///mdev_type +Date: October 2016 +Contact: Kirti Wankhede +Description: + This is symbolic link pointing to supported type, + directory of which this mediated device is created. + +What: /sys/...///remove +Date: October 2016 +Contact: Kirti Wankhede +Description: + Writing '1' to this file destroys the mediated device. The + vendor driver can fail the remove() callback if that device + is active and the vendor driver doesn't support hot unplug. + Example:: + + # echo 1 > /sys/bus/mdev/devices//remove -- cgit v1.3.1