Lines Matching +full:parameter +full:- +full:less
1 .. SPDX-License-Identifier: GPL-2.0
9 options that can be used to fine-tune the detector's operation. Finally,
20 - A CPU looping in an RCU read-side critical section.
22 - A CPU looping with interrupts disabled.
24 - A CPU looping with preemption disabled.
26 - A CPU looping with bottom halves disabled.
28 - For !CONFIG_PREEMPTION kernels, a CPU looping anywhere in the kernel
33 - Booting Linux using a console connection that is too slow to
34 keep up with the boot-time console-message rate. For example,
36 with boot-time message rates, and will frequently result in
40 - Anything that prevents RCU's grace-period kthreads from running.
41 This can result in the "All QSes seen" console-log message.
44 result in the ``rcu_.*kthread starved for`` console-log message,
47 - A CPU-bound real-time task in a CONFIG_PREEMPTION kernel, which might
48 happen to preempt a low-priority task in the middle of an RCU
49 read-side critical section. This is especially damaging if
50 that low-priority task is not permitted to run on any other CPU,
54 memory, you might see stall-warning messages.
56 - A CPU-bound real-time task in a CONFIG_PREEMPT_RT kernel that
62 CONFIG_PREEMPT_RCU case, you might see stall-warning
65 You can use the rcutree.kthread_prio kernel boot parameter to
68 can increase your system's context-switch rate and thus degrade
71 - A periodic interrupt whose handler takes longer than the time
74 Note that certain high-overhead debugging options, for example
79 - Testing a workload on a fast system, tuning the stall-warning
81 running the same workload with the same stall-warning timeout on a
82 slow system. Note that thermal throttling and on-demand governors
85 - A hardware or software issue shuts off the scheduler-clock
86 interrupt on a CPU that is not in dyntick-idle mode. This
90 - A hardware or software issue that prevents time-based wakeups
96 the ``rcu_.*timer wakeup didn't happen for`` console-log message,
99 - A bug in the RCU implementation.
101 - A hardware failure. This is quite unlikely, but has occurred
107 The RCU, RCU-sched, and RCU-tasks implementations have CPU stall warning.
125 Fine-Tuning the RCU CPU Stall Detector
128 The rcuupdate.rcu_cpu_stall_suppress module parameter disables RCU's
130 periods. This module parameter enables CPU stall detection by default,
131 but may be overridden via boot-time parameter or at runtime via sysfs.
136 ----------------------------
138 This kernel configuration parameter defines the period of time
143 This configuration parameter may be changed at runtime via the
145 this parameter is checked only at the beginning of a cycle.
146 So if you are 10 seconds into a 40-second stall, setting this
147 sysfs parameter to (say) five will shorten the timeout for the
152 Stall-warning messages may be enabled and disabled completely via
156 ---------------------
162 macro, not a kernel configuration parameter.)
165 -------------------
168 own warnings, as this often gives better-quality stack traces.
173 parameter.)
176 -------------------------------
178 This boot/sysfs parameter controls the RCU-tasks stall warning
179 interval. A value of zero or less suppresses RCU-tasks stall
180 warnings. A positive value sets the stall-warning interval
181 in seconds. An RCU-tasks stall warning starts with the line:
186 task stalling the current RCU-tasks grace period.
189 Interpreting RCU's CPU Stall-Detector "Splats"
192 For non-RCU-tasks flavors of RCU, when a CPU detects that some other
196 2-...: (3 GPs behind) idle=06c/0/0 softirq=1453/1455 fqs=0
197 16-...: (0 ticks this GP) idle=81c/0/0 softirq=764/764 fqs=0
201 causing stalls, and that the stall was affecting RCU-sched. This message
208 in a self-detected stall.
212 ticks this GP)" indicates that this CPU has not taken any scheduling-clock
215 The "idle=" portion of the message prints the dyntick-idle state.
216 The hex number before the first "/" is the low-order 12 bits of the
217 dynticks counter, which will have an even-numbered value if the CPU
218 is in dyntick-idle mode and an odd-numbered value otherwise. The hex
220 a small non-negative number if in the idle loop (as shown above) and a
228 example, if the CPU might have been in dyntick-idle mode for an extended
231 across repeated stall-warning messages, it is possible that RCU's softirq
233 the stalled CPU is spinning with interrupts are disabled, or, in -rt
234 kernels, if a high-priority process is starving RCU's softirq handler.
236 The "fqs=" shows the number of force-quiescent-state idle/offline
237 detection passes that the grace-period kthread has made across this
243 period (in this case 2603), the grace-period sequence number (7075), and
252 The "last_accelerate:" prints the low-order 16 bits (in hex) of the
255 rcu_prepare_for_idle(). "dyntick_enabled: 1" indicates that dyntick-idle
259 there will be a spurious stall-warning message, which will include
265 possible for a zero-jiffy stall to be flagged in this case, depending
266 on how the stall warning and the grace-period initialization happen to
272 grace period has nevertheless failed to end, the stall-warning splat
275 …n, last rcu_preempt kthread activity 23807 (4297905177-4297881370), jiffies_till_next_fqs=3, root …
278 since the grace-period kthread ran. The "jiffies_till_next_fqs"
280 of jiffies between force-quiescent-state scans, in this case three,
281 which is way less than 23807. Finally, the root rcu_node structure's
282 ->qsmask field is printed, which will normally be zero.
284 If the relevant grace-period kthread has been unable to run prior to
288 rcu_sched kthread starved for 23807 jiffies! g7075 f0x0 RCU_GP_WAIT_FQS(3) ->state=0x1 ->cpu=5
291 Starving the grace-period kthreads of CPU time can of course result
294 grace-period sequence number, the "f" precedes the ->gp_flags command
295 to the grace-period kthread, the "RCU_GP_WAIT_FQS" indicates that the
297 task_struct ->state field, and the "cpu" indicates that the grace-period
300 If the relevant grace-period kthread does not wake from FQS wait in a
303 kthread timer wakeup didn't happen for 23804 jiffies! g7076 f0x0 RCU_GP_WAIT_FQS(5) ->state=0x402
311 Possible timer handling issue on cpu=4 timer-softirq=11142
313 Here "cpu" indicates that the grace-period kthread last ran on CPU 4,
314 where it queued the fqs timer. The number following the "timer-softirq"
328 If a stall lasts long enough, multiple stall-warning messages will
342 INFO: rcu_sched detected expedited stalls on CPUs/tasks: { 7-... } 21119 jiffies s: 73 root: 0x2/.
353 grace-period sequence counter is 73. The fact that this last value is