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-tty | 166 ++++++++++++++++++++++++++++++++++++ 1 file changed, 166 insertions(+) create mode 100644 Documentation/ABI/testing/sysfs-tty (limited to 'Documentation/ABI/testing/sysfs-tty') diff --git a/Documentation/ABI/testing/sysfs-tty b/Documentation/ABI/testing/sysfs-tty new file mode 100644 index 000000000..895c47f05 --- /dev/null +++ b/Documentation/ABI/testing/sysfs-tty @@ -0,0 +1,166 @@ +What: /sys/class/tty/console/active +Date: Nov 2010 +Contact: Kay Sievers +Description: + Shows the list of currently configured + console devices, like 'tty1 ttyS0'. + The last entry in the file is the active + device connected to /dev/console. + The file supports poll() to detect virtual + console switches. + +What: /sys/class/tty/tty/active +Date: Nov 2010 +Contact: Kay Sievers +Description: + Shows the currently active virtual console + device, like 'tty1'. + The file supports poll() to detect virtual + console switches. + +What: /sys/class/tty/ttyS/uartclk +Date: Sep 2012 +Contact: Tomas Hlavacek +Description: + Shows the current uartclk value associated with the + UART port in serial_core, that is bound to TTY like ttyS0. + uartclk = 16 * baud_base + + These sysfs values expose the TIOCGSERIAL interface via + sysfs rather than via ioctls. + +What: /sys/class/tty/ttyS/type +Date: October 2012 +Contact: Alan Cox +Description: + Shows the current tty type for this port. + + These sysfs values expose the TIOCGSERIAL interface via + sysfs rather than via ioctls. + +What: /sys/class/tty/ttyS/line +Date: October 2012 +Contact: Alan Cox +Description: + Shows the current tty line number for this port. + + These sysfs values expose the TIOCGSERIAL interface via + sysfs rather than via ioctls. + +What: /sys/class/tty/ttyS/port +Date: October 2012 +Contact: Alan Cox +Description: + Shows the current tty port I/O address for this port. + + These sysfs values expose the TIOCGSERIAL interface via + sysfs rather than via ioctls. + +What: /sys/class/tty/ttyS/irq +Date: October 2012 +Contact: Alan Cox +Description: + Shows the current primary interrupt for this port. + + These sysfs values expose the TIOCGSERIAL interface via + sysfs rather than via ioctls. + +What: /sys/class/tty/ttyS/flags +Date: October 2012 +Contact: Alan Cox +Description: + Show the tty port status flags for this port. + + These sysfs values expose the TIOCGSERIAL interface via + sysfs rather than via ioctls. + +What: /sys/class/tty/ttyS/xmit_fifo_size +Date: October 2012 +Contact: Alan Cox +Description: + Show the transmit FIFO size for this port. + + These sysfs values expose the TIOCGSERIAL interface via + sysfs rather than via ioctls. + +What: /sys/class/tty/ttyS/close_delay +Date: October 2012 +Contact: Alan Cox +Description: + Show the closing delay time for this port in centiseconds. + + These sysfs values expose the TIOCGSERIAL interface via + sysfs rather than via ioctls. + +What: /sys/class/tty/ttyS/closing_wait +Date: October 2012 +Contact: Alan Cox +Description: + Show the close wait time for this port in centiseconds. + + Waiting forever is represented as 0. If waiting on close is + disabled then the value is 65535. + + These sysfs values expose the TIOCGSERIAL interface via + sysfs rather than via ioctls. + +What: /sys/class/tty/ttyS/custom_divisor +Date: October 2012 +Contact: Alan Cox +Description: + Show the custom divisor if any that is set on this port. + + These sysfs values expose the TIOCGSERIAL interface via + sysfs rather than via ioctls. + +What: /sys/class/tty/ttyS/io_type +Date: October 2012 +Contact: Alan Cox +Description: + Show the I/O type that is to be used with the iomem base + address. + + These sysfs values expose the TIOCGSERIAL interface via + sysfs rather than via ioctls. + +What: /sys/class/tty/ttyS/iomem_base +Date: October 2012 +Contact: Alan Cox +Description: + The I/O memory base for this port. + + These sysfs values expose the TIOCGSERIAL interface via + sysfs rather than via ioctls. + +What: /sys/class/tty/ttyS/iomem_reg_shift +Date: October 2012 +Contact: Alan Cox +Description: + Show the register shift indicating the spacing to be used + for accesses on this iomem address. + + These sysfs values expose the TIOCGSERIAL interface via + sysfs rather than via ioctls. + +What: /sys/class/tty/ttyS/rx_trig_bytes +Date: May 2014 +Contact: Yoshihiro YUNOMAE +Description: + Shows current RX interrupt trigger bytes or sets the + user specified value to change it for the FIFO buffer. + Users can show or set this value regardless of opening the + serial device file or not. + + The RX trigger can be set one of four kinds of values for UART + serials. When users input a meaning less value to this I/F, + the RX trigger is changed to the nearest lower value for the + device specification. For example, when user sets 7bytes on + 16550A, which has 1/4/8/14 bytes trigger, the RX trigger is + automatically changed to 4 bytes. + +What: /sys/class/tty/ttyS/console +Date: February 2020 +Contact: Andy Shevchenko +Description: + Allows user to detach or attach back the given device as + kernel console. It shows and accepts a boolean variable. -- cgit v1.3.1