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Message-Id: <1339786674-25265-1-git-send-email-paulmck@linux.vnet.ibm.com> Date: Fri, 15 Jun 2012 11:57:49 -0700 From: "Paul E. McKenney" <paulmck@...ux.vnet.ibm.com> To: linux-kernel@...r.kernel.org Cc: mingo@...e.hu, laijs@...fujitsu.com, dipankar@...ibm.com, akpm@...ux-foundation.org, mathieu.desnoyers@...ymtl.ca, josh@...htriplett.org, niv@...ibm.com, tglx@...utronix.de, peterz@...radead.org, rostedt@...dmis.org, Valdis.Kletnieks@...edu, dhowells@...hat.com, eric.dumazet@...il.com, darren@...art.com, fweisbec@...il.com, patches@...aro.org, "Paul E. McKenney" <paulmck@...ux.vnet.ibm.com> Subject: [PATCH tip/core/rcu 1/6] rcu: Update documentation to cover call_srcu() and srcu_barrier(). From: "Paul E. McKenney" <paulmck@...ux.vnet.ibm.com> The advent of call_srcu() and srcu_barrier() obsoleted some of the documentation, so this commit brings that up to date. Signed-off-by: Paul E. McKenney <paulmck@...ux.vnet.ibm.com> --- Documentation/RCU/checklist.txt | 39 +++++++++++++++++++------------------ Documentation/RCU/rcubarrier.txt | 6 +++- Documentation/RCU/torture.txt | 9 ++++++++ Documentation/RCU/whatisRCU.txt | 6 ++-- 4 files changed, 36 insertions(+), 24 deletions(-) diff --git a/Documentation/RCU/checklist.txt b/Documentation/RCU/checklist.txt index 5c8d749..fc103d7 100644 --- a/Documentation/RCU/checklist.txt +++ b/Documentation/RCU/checklist.txt @@ -162,9 +162,9 @@ over a rather long period of time, but improvements are always welcome! when publicizing a pointer to a structure that can be traversed by an RCU read-side critical section. -5. If call_rcu(), or a related primitive such as call_rcu_bh() or - call_rcu_sched(), is used, the callback function must be - written to be called from softirq context. In particular, +5. If call_rcu(), or a related primitive such as call_rcu_bh(), + call_rcu_sched(), or call_srcu() is used, the callback function + must be written to be called from softirq context. In particular, it cannot block. 6. Since synchronize_rcu() can block, it cannot be called from @@ -202,11 +202,12 @@ over a rather long period of time, but improvements are always welcome! updater uses call_rcu_sched() or synchronize_sched(), then the corresponding readers must disable preemption, possibly by calling rcu_read_lock_sched() and rcu_read_unlock_sched(). - If the updater uses synchronize_srcu(), the the corresponding - readers must use srcu_read_lock() and srcu_read_unlock(), - and with the same srcu_struct. The rules for the expedited - primitives are the same as for their non-expedited counterparts. - Mixing things up will result in confusion and broken kernels. + If the updater uses synchronize_srcu() or call_srcu(), + the the corresponding readers must use srcu_read_lock() and + srcu_read_unlock(), and with the same srcu_struct. The rules for + the expedited primitives are the same as for their non-expedited + counterparts. Mixing things up will result in confusion and + broken kernels. One exception to this rule: rcu_read_lock() and rcu_read_unlock() may be substituted for rcu_read_lock_bh() and rcu_read_unlock_bh() @@ -333,14 +334,14 @@ over a rather long period of time, but improvements are always welcome! victim CPU from ever going offline.) 14. SRCU (srcu_read_lock(), srcu_read_unlock(), srcu_dereference(), - synchronize_srcu(), and synchronize_srcu_expedited()) may only - be invoked from process context. Unlike other forms of RCU, it - -is- permissible to block in an SRCU read-side critical section - (demarked by srcu_read_lock() and srcu_read_unlock()), hence the - "SRCU": "sleepable RCU". Please note that if you don't need - to sleep in read-side critical sections, you should be using - RCU rather than SRCU, because RCU is almost always faster and - easier to use than is SRCU. + synchronize_srcu(), synchronize_srcu_expedited(), and call_srcu()) + may only be invoked from process context. Unlike other forms of + RCU, it -is- permissible to block in an SRCU read-side critical + section (demarked by srcu_read_lock() and srcu_read_unlock()), + hence the "SRCU": "sleepable RCU". Please note that if you + don't need to sleep in read-side critical sections, you should be + using RCU rather than SRCU, because RCU is almost always faster + and easier to use than is SRCU. If you need to enter your read-side critical section in a hardirq or exception handler, and then exit that same read-side @@ -353,8 +354,8 @@ over a rather long period of time, but improvements are always welcome! cleanup_srcu_struct(). These are passed a "struct srcu_struct" that defines the scope of a given SRCU domain. Once initialized, the srcu_struct is passed to srcu_read_lock(), srcu_read_unlock() - synchronize_srcu(), and synchronize_srcu_expedited(). A given - synchronize_srcu() waits only for SRCU read-side critical + synchronize_srcu(), synchronize_srcu_expedited(), and call_srcu(). + A given synchronize_srcu() waits only for SRCU read-side critical sections governed by srcu_read_lock() and srcu_read_unlock() calls that have been passed the same srcu_struct. This property is what makes sleeping read-side critical sections tolerable -- @@ -374,7 +375,7 @@ over a rather long period of time, but improvements are always welcome! requiring SRCU's read-side deadlock immunity or low read-side realtime latency. - Note that, rcu_assign_pointer() relates to SRCU just as they do + Note that, rcu_assign_pointer() relates to SRCU just as it does to other forms of RCU. 15. The whole point of call_rcu(), synchronize_rcu(), and friends diff --git a/Documentation/RCU/rcubarrier.txt b/Documentation/RCU/rcubarrier.txt index e439a0e..a511fe6 100644 --- a/Documentation/RCU/rcubarrier.txt +++ b/Documentation/RCU/rcubarrier.txt @@ -261,8 +261,10 @@ Answers to Quick Quizzes Quick Quiz #1: Why is there no srcu_barrier()? -Answer: Since there is no call_srcu(), there can be no outstanding SRCU - callbacks. Therefore, there is no need to wait for them. +Answer: There really is an srcu_barrier() now that there is a call_srcu(). + Before call_srcu(), there were no SRCU callbacks, and there was + therefore no need to wait for them, and therefore there was + no srcu_barrier(). Quick Quiz #2: Is there any other situation where rcu_barrier() might be required? diff --git a/Documentation/RCU/torture.txt b/Documentation/RCU/torture.txt index 4ddf391..7dce8a1 100644 --- a/Documentation/RCU/torture.txt +++ b/Documentation/RCU/torture.txt @@ -174,11 +174,20 @@ torture_type The type of RCU to test, with string values as follows: and synchronize_rcu_bh_expedited(). "srcu": srcu_read_lock(), srcu_read_unlock() and + call_srcu(). + + "srcu_sync": srcu_read_lock(), srcu_read_unlock() and synchronize_srcu(). "srcu_expedited": srcu_read_lock(), srcu_read_unlock() and synchronize_srcu_expedited(). + "srcu_raw": srcu_read_lock_raw(), srcu_read_unlock_raw(), + and call_srcu(). + + "srcu_raw_sync": srcu_read_lock_raw(), srcu_read_unlock_raw(), + and synchronize_srcu(). + "sched": preempt_disable(), preempt_enable(), and call_rcu_sched(). diff --git a/Documentation/RCU/whatisRCU.txt b/Documentation/RCU/whatisRCU.txt index 6bbe8dc..69ee188 100644 --- a/Documentation/RCU/whatisRCU.txt +++ b/Documentation/RCU/whatisRCU.txt @@ -833,9 +833,9 @@ sched: Critical sections Grace period Barrier SRCU: Critical sections Grace period Barrier - srcu_read_lock synchronize_srcu N/A - srcu_read_unlock synchronize_srcu_expedited - srcu_read_lock_raw + srcu_read_lock synchronize_srcu srcu_barrier + srcu_read_unlock call_srcu + srcu_read_lock_raw synchronize_srcu_expedited srcu_read_unlock_raw srcu_dereference -- 1.7.8 -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@...r.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
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