From: "Joel Fernandes (Google)" <joel@joelfernandes.org>
To: linux-kernel@vger.kernel.org
Cc: "Joel Fernandes (Google)" <joel@joelfernandes.org>,
"Paul E. McKenney" <paulmck@linux.vnet.ibm.com>,
Josh Triplett <josh@joshtriplett.org>,
Steven Rostedt <rostedt@goodmis.org>,
Mathieu Desnoyers <mathieu.desnoyers@efficios.com>,
Lai Jiangshan <jiangshanlai@gmail.com>,
byungchul.park@lge.com, kernel-team@android.com
Subject: [PATCH RFC 2/8] rcu: Clarify usage of cond_resched for tasks-RCU
Date: Sun, 13 May 2018 20:15:35 -0700 [thread overview]
Message-ID: <20180514031541.67247-3-joel@joelfernandes.org> (raw)
In-Reply-To: <20180514031541.67247-1-joel@joelfernandes.org>
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.park@lge.com
Signed-off-by: Joel Fernandes (Google) <joel@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
next prev parent reply other threads:[~2018-05-14 3:16 UTC|newest]
Thread overview: 42+ messages / expand[flat|nested] mbox.gz Atom feed top
2018-05-14 3:15 [PATCH RFC 0/8] rcu fixes, clean ups for rcu/dev Joel Fernandes (Google)
2018-05-14 3:15 ` [PATCH RFC 1/8] rcu: Add comment documenting how rcu_seq_snap works Joel Fernandes (Google)
2018-05-14 3:47 ` Randy Dunlap
2018-05-14 5:05 ` Joel Fernandes
2018-05-14 17:38 ` Paul E. McKenney
2018-05-15 1:51 ` Joel Fernandes
2018-05-15 3:59 ` Paul E. McKenney
2018-05-15 7:02 ` Joel Fernandes
2018-05-15 12:55 ` Paul E. McKenney
2018-05-15 18:41 ` Joel Fernandes
2018-05-15 19:08 ` Paul E. McKenney
2018-05-15 22:55 ` Joel Fernandes
2018-05-16 15:45 ` Paul E. McKenney
2018-05-16 23:21 ` Joel Fernandes
2018-05-14 3:15 ` Joel Fernandes (Google) [this message]
2018-05-14 14:54 ` [PATCH RFC 2/8] rcu: Clarify usage of cond_resched for tasks-RCU Steven Rostedt
2018-05-14 17:22 ` Paul E. McKenney
2018-05-15 0:35 ` Joel Fernandes
2018-05-15 3:42 ` Paul E. McKenney
2018-05-14 3:15 ` [PATCH RFC 3/8] rcu: Add back the cpuend tracepoint Joel Fernandes (Google)
2018-05-14 18:12 ` Paul E. McKenney
2018-05-15 0:43 ` Joel Fernandes
2018-05-14 3:15 ` [PATCH RFC 4/8] rcu: Get rid of old c variable from places in tree RCU Joel Fernandes (Google)
2018-05-14 17:57 ` Paul E. McKenney
2018-05-15 0:41 ` Joel Fernandes
2018-05-14 3:15 ` [PATCH RFC 5/8] rcu: Use rcu_node as temporary variable in funnel locking loop Joel Fernandes (Google)
2018-05-14 18:00 ` Paul E. McKenney
2018-05-15 0:43 ` Joel Fernandes
2018-05-14 3:15 ` [PATCH RFC 6/8] rcu: Add back the Startedleaf tracepoint Joel Fernandes (Google)
2018-05-14 18:38 ` Paul E. McKenney
2018-05-15 0:57 ` Joel Fernandes
2018-05-15 3:46 ` Paul E. McKenney
2018-05-15 23:04 ` Joel Fernandes
2018-05-16 15:48 ` Paul E. McKenney
2018-05-16 23:13 ` Joel Fernandes
2018-05-14 3:15 ` [PATCH RFC 7/8] rcu: trace CleanupMore condition only if needed Joel Fernandes (Google)
2018-05-14 19:20 ` Paul E. McKenney
2018-05-15 1:01 ` Joel Fernandes
2018-05-15 3:47 ` Paul E. McKenney
2018-05-14 3:15 ` [PATCH RFC 8/8] rcu: Fix cpustart tracepoint gp_seq number Joel Fernandes (Google)
2018-05-14 20:33 ` Paul E. McKenney
2018-05-15 1:02 ` Joel Fernandes
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