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-rnbd-client | 133 ++++++++++++++++++++++ 1 file changed, 133 insertions(+) create mode 100644 Documentation/ABI/testing/sysfs-class-rnbd-client (limited to 'Documentation/ABI/testing/sysfs-class-rnbd-client') diff --git a/Documentation/ABI/testing/sysfs-class-rnbd-client b/Documentation/ABI/testing/sysfs-class-rnbd-client new file mode 100644 index 000000000..0b5997ab3 --- /dev/null +++ b/Documentation/ABI/testing/sysfs-class-rnbd-client @@ -0,0 +1,133 @@ +What: /sys/class/rnbd-client +Date: Feb 2020 +KernelVersion: 5.7 +Contact: Jack Wang Danil Kipnis +Description: Provide information about RNBD-client. + All sysfs files that are not read-only provide the usage information on read: + + Example:: + + # cat /sys/class/rnbd-client/ctl/map_device + + > Usage: echo "sessname= path=<[srcaddr,]dstaddr> + > [path=<[srcaddr,]dstaddr>] device_path= + > [access_mode=] > map_device + > + > addr ::= [ ip: | ip: | gid: ] + +What: /sys/class/rnbd-client/ctl/map_device +Date: Feb 2020 +KernelVersion: 5.7 +Contact: Jack Wang Danil Kipnis +Description: Expected format is the following:: + + sessname= + path=<[srcaddr,]dstaddr> [path=<[srcaddr,]dstaddr> ...] + device_path= + [access_mode=] + + Where: + + sessname: + accepts a string not bigger than 256 chars, which identifies + a given session on the client and on the server. + I.e. "clt_hostname-srv_hostname" could be a natural choice. + + path: + describes a connection between the client and the server by + specifying destination and, when required, the source address. + The addresses are to be provided in the following format:: + + ip: + ip: + gid: + + for example:: + + path=ip:10.0.0.66 + + The single addr is treated as the destination. + The connection will be established to this server from any client IP address. + + :: + + path=ip:10.0.0.66,ip:10.0.1.66 + + First addr is the source address and the second is the destination. + + If multiple "path=" options are specified multiple connection + will be established and data will be sent according to + the selected multipath policy (see RTRS mp_policy sysfs entry description). + + device_path: + Path to the block device on the server side. Path is specified + relative to the directory on server side configured in the + 'dev_search_path' module parameter of the rnbd_server. + The rnbd_server prepends the received from client + with and tries to open the + / block device. On success, + a /dev/rnbd device file, a /sys/block/rnbd/ + directory and an entry in /sys/class/rnbd-client/ctl/devices + will be created. + + If 'dev_search_path' contains '%SESSNAME%', then each session can + have different devices namespace, e.g. server was configured with + the following parameter "dev_search_path=/run/rnbd-devs/%SESSNAME%", + client has this string "sessname=blya device_path=sda", then server + will try to open: /run/rnbd-devs/blya/sda. + + access_mode: + the access_mode parameter specifies if the device is to be + mapped as "ro" read-only or "rw" read-write. The server allows + a device to be exported in rw mode only once. The "migration" + access mode has to be specified if a second mapping in read-write + mode is desired. + + By default "rw" is used. + + nr_poll_queues + specifies the number of poll-mode queues. If the IO has HIPRI flag, + the block-layer will send the IO via the poll-mode queue. + For fast network and device the polling is faster than interrupt-base + IO handling because it saves time for context switching, switching to + another process, handling the interrupt and switching back to the + issuing process. + + Set -1 if you want to set it as the number of CPUs + By default rnbd client creates only irq-mode queues. + + NOTICE: MUST make a unique session for a device using the poll-mode queues. + + Exit Codes: + + If the device is already mapped it will fail with EEXIST. If the input + has an invalid format it will return EINVAL. If the device path cannot + be found on the server, it will fail with ENOENT. + + Finding device file after mapping + --------------------------------- + + After mapping, the device file can be found by: + o The symlink /sys/class/rnbd-client/ctl/devices/@ + points to /sys/block/. The last part of the symlink destination + is the same as the device name. By extracting the last part of the + path the path to the device /dev/ can be build. + + * /dev/block/$(cat /sys/class/rnbd-client/ctl/devices/@/dev) + + How to find the of the device is described on the next + section. + +What: /sys/class/rnbd-client/ctl/devices/ +Date: Feb 2020 +KernelVersion: 5.7 +Contact: Jack Wang Danil Kipnis +Description: For each device mapped on the client a new symbolic link is created as + /sys/class/rnbd-client/ctl/devices/@, which points + to the block device created by rnbd (/sys/block/rnbd/). + The of each device is created as follows: + + - If the 'device_path' provided during mapping contains slashes ("/"), + they are replaced by exclamation mark ("!") and used as as the + . Otherwise, the will be the same as the + "device_path" provided. -- cgit v1.3.1