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The rcu_preempt_deferred_qs_irqrestore() function is invoked at the end of an RCU read-side critical section (for example, directly from rcu_read_unlock()) and, if .need_qs is set, invokes rcu_qs() to report the new quiescent state. This works, except that rcu_qs() only updates per-CPU state, leaving reporting of the actual quiescent state to a later call to rcu_report_qs_rdp(), for example from within a later RCU_SOFTIRQ instance. Although this approach is exactly what you want if you are more concerned about efficiency than about short grace periods, in CONFIG_RCU_STRICT_GRACE_PERIOD=y kernels, short grace periods are the name of the game. This commit therefore makes rcu_preempt_deferred_qs_irqrestore() directly invoke rcu_report_qs_rdp() in CONFIG_RCU_STRICT_GRACE_PERIOD=y, thus shortening grace periods. Historical note: To the best of my knowledge, causing rcu_read_unlock() to directly report a quiescent state first appeared in Jim Houston's and Joe Korty's JRCU. This is the second instance of a Linux-kernel RCU feature being inspired by JRCU, the first being RCU callback offloading (as in the RCU_NOCB_CPU Kconfig option). Reported-by Jann Horn <jannh@google.com> Signed-off-by: Paul E. McKenney <paulmck@kernel.org> |
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| .. | ||
| Kconfig | ||
| Kconfig.debug | ||
| Makefile | ||
| rcu.h | ||
| rcu_segcblist.c | ||
| rcu_segcblist.h | ||
| rcuperf.c | ||
| rcutorture.c | ||
| refscale.c | ||
| srcutiny.c | ||
| srcutree.c | ||
| sync.c | ||
| tasks.h | ||
| tiny.c | ||
| tree.c | ||
| tree.h | ||
| tree_exp.h | ||
| tree_plugin.h | ||
| tree_stall.h | ||
| update.c | ||