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-class-mic | 178 ++++++++++++++++++++++++++++++ 1 file changed, 178 insertions(+) create mode 100644 Documentation/ABI/testing/sysfs-class-mic (limited to 'Documentation/ABI/testing/sysfs-class-mic') diff --git a/Documentation/ABI/testing/sysfs-class-mic b/Documentation/ABI/testing/sysfs-class-mic new file mode 100644 index 000000000..5e5f36d10 --- /dev/null +++ b/Documentation/ABI/testing/sysfs-class-mic @@ -0,0 +1,178 @@ +What: /sys/class/mic/ +Date: October 2013 +KernelVersion: 3.13 +Contact: Sudeep Dutt +Description: + The mic class directory belongs to Intel MIC devices and + provides information per MIC device. An Intel MIC device is a + PCIe form factor add-in Coprocessor card based on the Intel Many + Integrated Core (MIC) architecture that runs a Linux OS. + +What: /sys/class/mic/mic +Date: October 2013 +KernelVersion: 3.13 +Contact: Sudeep Dutt +Description: + The directories /sys/class/mic/mic0, /sys/class/mic/mic1 etc., + represent MIC devices (0,1,..etc). Each directory has + information specific to that MIC device. + +What: /sys/class/mic/mic/family +Date: October 2013 +KernelVersion: 3.13 +Contact: Sudeep Dutt +Description: + Provides information about the Coprocessor family for an Intel + MIC device. For example - "x100" + +What: /sys/class/mic/mic/stepping +Date: October 2013 +KernelVersion: 3.13 +Contact: Sudeep Dutt +Description: + Provides information about the silicon stepping for an Intel + MIC device. For example - "A0" or "B0" + +What: /sys/class/mic/mic/state +Date: October 2013 +KernelVersion: 3.13 +Contact: Sudeep Dutt +Description: + When read, this entry provides the current state of an Intel + MIC device in the context of the card OS. Possible values that + will be read are: + + + =============== =============================================== + "ready" The MIC device is ready to boot the card OS. + On reading this entry after an OSPM resume, + a "boot" has to be written to this entry if + the card was previously shutdown during OSPM + suspend. + "booting" The MIC device has initiated booting a card OS. + "online" The MIC device has completed boot and is online + "shutting_down" The card OS is shutting down. + "resetting" A reset has been initiated for the MIC device + "reset_failed" The MIC device has failed to reset. + =============== =============================================== + + When written, this sysfs entry triggers different state change + operations depending upon the current state of the card OS. + Acceptable values are: + + + ========== =================================================== + "boot" Boot the card OS image specified by the combination + of firmware, ramdisk, cmdline and bootmode + sysfs entries. + "reset" Initiates device reset. + "shutdown" Initiates card OS shutdown. + ========== =================================================== + +What: /sys/class/mic/mic/shutdown_status +Date: October 2013 +KernelVersion: 3.13 +Contact: Sudeep Dutt +Description: + An Intel MIC device runs a Linux OS during its operation. This + OS can shutdown because of various reasons. When read, this + entry provides the status on why the card OS was shutdown. + Possible values are: + + ========== =================================================== + "nop" shutdown status is not applicable, when the card OS + is "online" + "crashed" Shutdown because of a HW or SW crash. + "halted" Shutdown because of a halt command. + "poweroff" Shutdown because of a poweroff command. + "restart" Shutdown because of a restart command. + ========== =================================================== + +What: /sys/class/mic/mic/cmdline +Date: October 2013 +KernelVersion: 3.13 +Contact: Sudeep Dutt +Description: + An Intel MIC device runs a Linux OS during its operation. Before + booting this card OS, it is possible to pass kernel command line + options to configure various features in it, similar to + self-bootable machines. When read, this entry provides + information about the current kernel command line options set to + boot the card OS. This entry can be written to change the + existing kernel command line options. Typically, the user would + want to read the current command line options, append new ones + or modify existing ones and then write the whole kernel command + line back to this entry. + +What: /sys/class/mic/mic/firmware +Date: October 2013 +KernelVersion: 3.13 +Contact: Sudeep Dutt +Description: + When read, this sysfs entry provides the path name under + /lib/firmware/ where the firmware image to be booted on the + card can be found. The entry can be written to change the + firmware image location under /lib/firmware/. + +What: /sys/class/mic/mic/ramdisk +Date: October 2013 +KernelVersion: 3.13 +Contact: Sudeep Dutt +Description: + When read, this sysfs entry provides the path name under + /lib/firmware/ where the ramdisk image to be used during card + OS boot can be found. The entry can be written to change + the ramdisk image location under /lib/firmware/. + +What: /sys/class/mic/mic/bootmode +Date: October 2013 +KernelVersion: 3.13 +Contact: Sudeep Dutt +Description: + When read, this sysfs entry provides the current bootmode for + the card. This sysfs entry can be written with the following + valid strings: + a) linux - Boot a Linux image. + b) flash - Boot an image for flash updates. + +What: /sys/class/mic/mic/log_buf_addr +Date: October 2013 +KernelVersion: 3.13 +Contact: Sudeep Dutt +Description: + An Intel MIC device runs a Linux OS during its operation. For + debugging purpose and early kernel boot messages, the user can + access the card OS log buffer via debugfs. When read, this entry + provides the kernel virtual address of the buffer where the card + OS log buffer can be read. This entry is written by the host + configuration daemon to set the log buffer address. The correct + log buffer address to be written can be found in the System.map + file of the card OS. + +What: /sys/class/mic/mic/log_buf_len +Date: October 2013 +KernelVersion: 3.13 +Contact: Sudeep Dutt +Description: + An Intel MIC device runs a Linux OS during its operation. For + debugging purpose and early kernel boot messages, the user can + access the card OS log buffer via debugfs. When read, this entry + provides the kernel virtual address where the card OS log buffer + length can be read. This entry is written by host configuration + daemon to set the log buffer length address. The correct log + buffer length address to be written can be found in the + System.map file of the card OS. + +What: /sys/class/mic/mic/heartbeat_enable +Date: March 2015 +KernelVersion: 4.4 +Contact: Ashutosh Dixit +Description: + The MIC drivers detect and inform user space about card crashes + via a heartbeat mechanism (see the description of + shutdown_status above). User space can turn off this + notification by setting heartbeat_enable to 0 and enable it by + setting this entry to 1. If this notification is disabled it is + the responsibility of user space to detect card crashes via + alternative means such as a network ping. This setting is + enabled by default. -- cgit v1.3.1