Commit 28b3ae42 authored by Uladzislau Rezki's avatar Uladzislau Rezki Committed by Paul E. McKenney
Browse files

rcu: Introduce CONFIG_RCU_EXP_CPU_STALL_TIMEOUT 



Currently both expedited and regular grace period stall warnings use
a single timeout value that with units of seconds.  However, recent
Android use cases problem require a sub-100-millisecond expedited RCU CPU
stall warning.  Given that expedited RCU grace periods normally complete
in far less than a single millisecond, especially for small systems,
this is not unreasonable.

Therefore introduce the CONFIG_RCU_EXP_CPU_STALL_TIMEOUT kernel
configuration that defaults to 20 msec on Android and remains the same
as that of the non-expedited stall warnings otherwise.  It also can be
changed in run-time via: /sys/.../parameters/rcu_exp_cpu_stall_timeout.

[ paulmck: Default of zero to use CONFIG_RCU_STALL_TIMEOUT. ]

Signed-off-by: default avatarUladzislau Rezki <uladzislau.rezki@sony.com>
Signed-off-by: default avatarUladzislau Rezki (Sony) <urezki@gmail.com>
Signed-off-by: default avatarPaul E. McKenney <paulmck@kernel.org>
parent 31231092

Documentation/RCU/stallwarn.rst

+20 −0
Original line number Diff line number Diff line
@@ -162,6 +162,26 @@ CONFIG_RCU_CPU_STALL_TIMEOUT 
	Stall-warning messages may be enabled and disabled completely via

	/sys/module/rcupdate/parameters/rcu_cpu_stall_suppress.



CONFIG_RCU_EXP_CPU_STALL_TIMEOUT

--------------------------------



	Same as the CONFIG_RCU_CPU_STALL_TIMEOUT parameter but only for

	the expedited grace period. This parameter defines the period

	of time that RCU will wait from the beginning of an expedited

	grace period until it issues an RCU CPU stall warning. This time

	period is normally 20 milliseconds on Android devices.	A zero

	value causes the CONFIG_RCU_CPU_STALL_TIMEOUT value to be used,

	after conversion to milliseconds.



	This configuration parameter may be changed at runtime via the

	/sys/module/rcupdate/parameters/rcu_exp_cpu_stall_timeout, however

	this parameter is checked only at the beginning of a cycle. If you

	are in a current stall cycle, setting it to a new value will change

	the timeout for the -next- stall.



	Stall-warning messages may be enabled and disabled completely via

	/sys/module/rcupdate/parameters/rcu_cpu_stall_suppress.



RCU_STALL_DELAY_DELTA

---------------------

Documentation/admin-guide/kernel-parameters.txt

+12 −0
Original line number Diff line number Diff line
@@ -4893,6 +4893,18 @@ 


	rcupdate.rcu_cpu_stall_timeout= [KNL]

			Set timeout for RCU CPU stall warning messages.

			The value is in seconds and the maximum allowed

			value is 300 seconds.



	rcupdate.rcu_exp_cpu_stall_timeout= [KNL]

			Set timeout for expedited RCU CPU stall warning

			messages.  The value is in milliseconds

			and the maximum allowed value is 21000

			milliseconds. Please note that this value is

			adjusted to an arch timer tick resolution.

			Setting this to zero causes the value from

			rcupdate.rcu_cpu_stall_timeout to be used (after

			conversion from seconds to milliseconds).



	rcupdate.rcu_expedited= [KNL]

			Use expedited grace-period primitives, for

kernel/rcu/Kconfig.debug

+14 −0
Original line number Diff line number Diff line
@@ -91,6 +91,20 @@ config RCU_CPU_STALL_TIMEOUT 
	  RCU grace period persists, additional CPU stall warnings are

	  printed at more widely spaced intervals.



config RCU_EXP_CPU_STALL_TIMEOUT

	int "Expedited RCU CPU stall timeout in milliseconds"

	depends on RCU_STALL_COMMON

	range 0 21000

	default 20 if ANDROID

	default 0 if !ANDROID

	help

	  If a given expedited RCU grace period extends more than the

	  specified number of milliseconds, a CPU stall warning is printed.

	  If the RCU grace period persists, additional CPU stall warnings

	  are printed at more widely spaced intervals.  A value of zero

	  says to use the RCU_CPU_STALL_TIMEOUT value converted from

	  seconds to milliseconds.



config RCU_TRACE

	bool "Enable tracing for RCU"

	depends on DEBUG_KERNEL

kernel/rcu/rcu.h

+2 −0
Original line number Diff line number Diff line
@@ -210,7 +210,9 @@ static inline bool rcu_stall_is_suppressed_at_boot(void) 
extern int rcu_cpu_stall_ftrace_dump;

extern int rcu_cpu_stall_suppress;

extern int rcu_cpu_stall_timeout;

extern int rcu_exp_cpu_stall_timeout;

int rcu_jiffies_till_stall_check(void);

int rcu_exp_jiffies_till_stall_check(void);



static inline bool rcu_stall_is_suppressed(void)

{

kernel/rcu/tree_exp.h

+2 −2
Original line number Diff line number Diff line
@@ -496,7 +496,7 @@ static void synchronize_rcu_expedited_wait(void) 
	struct rcu_node *rnp_root = rcu_get_root();



	trace_rcu_exp_grace_period(rcu_state.name, rcu_exp_gp_seq_endval(), TPS("startwait"));

	jiffies_stall = rcu_jiffies_till_stall_check();

	jiffies_stall = rcu_exp_jiffies_till_stall_check();

	jiffies_start = jiffies;

	if (tick_nohz_full_enabled() && rcu_inkernel_boot_has_ended()) {

		if (synchronize_rcu_expedited_wait_once(1))
@@ -571,7 +571,7 @@ static void synchronize_rcu_expedited_wait(void) 
				dump_cpu_task(cpu);

			}

		}

		jiffies_stall = 3 * rcu_jiffies_till_stall_check() + 3;

		jiffies_stall = 3 * rcu_exp_jiffies_till_stall_check() + 3;

	}

}