Recently we had a discussion about cond_resched unconditionally recording a voluntary context switch [1].
Lets add a comment clarifying that how this API is to be used. [1] https://lkml.kernel.org/r/1526027434-21237-1-git-send-email-byungchul.p...@lge.com Signed-off-by: Joel Fernandes (Google) <j...@joelfernandes.org> --- include/linux/rcupdate.h | 11 ++++++++--- 1 file changed, 8 insertions(+), 3 deletions(-) diff --git a/include/linux/rcupdate.h b/include/linux/rcupdate.h index 743226176350..a9881007ece6 100644 --- a/include/linux/rcupdate.h +++ b/include/linux/rcupdate.h @@ -159,8 +159,12 @@ static inline void rcu_init_nohz(void) { } } while (0) /* - * Note a voluntary context switch for RCU-tasks benefit. This is a - * macro rather than an inline function to avoid #include hell. + * Note an attempt to perform a voluntary context switch for RCU-tasks benefit. + * + * This is called even in situations where a context switch didn't really + * happen even though it was requested. The caller uses it to indicate + * traversal of an RCU-tasks quiescent state. This is a macro rather than an + * inline function to avoid #include hell. */ #ifdef CONFIG_TASKS_RCU #define rcu_note_voluntary_context_switch_lite(t) \ @@ -187,7 +191,8 @@ static inline void exit_tasks_rcu_finish(void) { } #endif /* #else #ifdef CONFIG_TASKS_RCU */ /** - * cond_resched_tasks_rcu_qs - Report potential quiescent states to RCU + * cond_resched_tasks_rcu_qs - Report potential quiescent states to RCU. + * The quiescent state report is made even if cond_resched() did nothing. * * This macro resembles cond_resched(), except that it is defined to * report potential quiescent states to RCU-tasks even if the cond_resched() -- 2.17.0.441.gb46fe60e1d-goog
