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authorPaul E. McKenney <paulmck@kernel.org>2019-11-28 03:36:45 +0300
committerPaul E. McKenney <paulmck@kernel.org>2019-12-09 23:32:59 +0300
commitdf1e849ae4559544ff00ff5052eefe2479750539 (patch)
treebe1bac3d41c0d6daec68af70e174ff0896599430 /include/linux/tick.h
parent28f0361fdfab267a392cd6a6401446c9ea64de95 (diff)
downloadlinux-df1e849ae4559544ff00ff5052eefe2479750539.tar.xz
rcu: Enable tick for nohz_full CPUs slow to provide expedited QS
An expedited grace period can be stalled by a nohz_full CPU looping in kernel context. This possibility is currently handled by some carefully crafted checks in rcu_read_unlock_special() that enlist help from ksoftirqd when permitted by the scheduler. However, it is exactly these checks that require the scheduler avoid holding any of its rq or pi locks across rcu_read_unlock() without also having held them across the entire RCU read-side critical section. It would therefore be very nice if expedited grace periods could handle nohz_full CPUs looping in kernel context without such checks. This commit therefore adds code to the expedited grace period's wait and cleanup code that forces the scheduler-clock interrupt on for CPUs that fail to quickly supply a quiescent state. "Quickly" is currently a hard-coded single-jiffy delay. Signed-off-by: Paul E. McKenney <paulmck@kernel.org>
Diffstat (limited to 'include/linux/tick.h')
-rw-r--r--include/linux/tick.h5
1 files changed, 4 insertions, 1 deletions
diff --git a/include/linux/tick.h b/include/linux/tick.h
index 7896f792d3b0..7340613c7eff 100644
--- a/include/linux/tick.h
+++ b/include/linux/tick.h
@@ -109,8 +109,10 @@ enum tick_dep_bits {
TICK_DEP_BIT_PERF_EVENTS = 1,
TICK_DEP_BIT_SCHED = 2,
TICK_DEP_BIT_CLOCK_UNSTABLE = 3,
- TICK_DEP_BIT_RCU = 4
+ TICK_DEP_BIT_RCU = 4,
+ TICK_DEP_BIT_RCU_EXP = 5
};
+#define TICK_DEP_BIT_MAX TICK_DEP_BIT_RCU_EXP
#define TICK_DEP_MASK_NONE 0
#define TICK_DEP_MASK_POSIX_TIMER (1 << TICK_DEP_BIT_POSIX_TIMER)
@@ -118,6 +120,7 @@ enum tick_dep_bits {
#define TICK_DEP_MASK_SCHED (1 << TICK_DEP_BIT_SCHED)
#define TICK_DEP_MASK_CLOCK_UNSTABLE (1 << TICK_DEP_BIT_CLOCK_UNSTABLE)
#define TICK_DEP_MASK_RCU (1 << TICK_DEP_BIT_RCU)
+#define TICK_DEP_MASK_RCU_EXP (1 << TICK_DEP_BIT_RCU_EXP)
#ifdef CONFIG_NO_HZ_COMMON
extern bool tick_nohz_enabled;