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McKenney" To: linux-kernel@vger.kernel.org Cc: mingo@kernel.org, jiangshanlai@gmail.com, dipankar@in.ibm.com, akpm@linux-foundation.org, mathieu.desnoyers@efficios.com, josh@joshtriplett.org, tglx@linutronix.de, peterz@infradead.org, rostedt@goodmis.org, dhowells@redhat.com, edumazet@google.com, fweisbec@gmail.com, oleg@redhat.com, joel@joelfernandes.org, "Paul E. McKenney" Subject: [PATCH tip/core/rcu 07/12] rcu: Update NOCB comments Date: Wed, 9 Jan 2019 13:28:29 -0800 X-Mailer: git-send-email 2.17.1 In-Reply-To: <20190109212816.GA32282@linux.ibm.com> References: <20190109212816.GA32282@linux.ibm.com> X-TM-AS-GCONF: 00 x-cbid: 19010921-0064-0000-0000-0000039410D7 X-IBM-SpamModules-Scores: X-IBM-SpamModules-Versions: BY=3.00010375; HX=3.00000242; KW=3.00000007; PH=3.00000004; SC=3.00000274; SDB=6.01144145; UDB=6.00595708; IPR=6.00924407; MB=3.00025056; MTD=3.00000008; XFM=3.00000015; UTC=2019-01-09 21:28:40 X-IBM-AV-DETECTION: SAVI=unused REMOTE=unused XFE=unused x-cbparentid: 19010921-0065-0000-0000-00003BF962E2 Message-Id: <20190109212834.1257-7-paulmck@linux.ibm.com> X-Proofpoint-Virus-Version: vendor=fsecure engine=2.50.10434:,, definitions=2019-01-09_10:,, signatures=0 X-Proofpoint-Spam-Details: rule=outbound_notspam policy=outbound score=0 priorityscore=1501 malwarescore=0 suspectscore=1 phishscore=0 bulkscore=0 spamscore=0 clxscore=1015 lowpriorityscore=0 mlxscore=0 impostorscore=0 mlxlogscore=999 adultscore=0 classifier=spam adjust=0 reason=mlx scancount=1 engine=8.0.1-1810050000 definitions=main-1901090171 Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org This commit updates a few obsolete comments in the RCU callback-offload code. Signed-off-by: Paul E. McKenney --- kernel/rcu/tree_plugin.h | 33 ++++++++++++++++----------------- 1 file changed, 16 insertions(+), 17 deletions(-) diff --git a/kernel/rcu/tree_plugin.h b/kernel/rcu/tree_plugin.h index b241c4b20549..f0019c2a2cbc 100644 --- a/kernel/rcu/tree_plugin.h +++ b/kernel/rcu/tree_plugin.h @@ -1857,22 +1857,24 @@ static void zero_cpu_stall_ticks(struct rcu_data *rdp) /* * Offload callback processing from the boot-time-specified set of CPUs - * specified by rcu_nocb_mask. For each CPU in the set, there is a - * kthread created that pulls the callbacks from the corresponding CPU, - * waits for a grace period to elapse, and invokes the callbacks. - * The no-CBs CPUs do a wake_up() on their kthread when they insert - * a callback into any empty list, unless the rcu_nocb_poll boot parameter - * has been specified, in which case each kthread actively polls its - * CPU. (Which isn't so great for energy efficiency, but which does - * reduce RCU's overhead on that CPU.) + * specified by rcu_nocb_mask. For the CPUs in the set, there are kthreads + * created that pull the callbacks from the corresponding CPU, wait for + * a grace period to elapse, and invoke the callbacks. These kthreads + * are organized into leaders, which manage incoming callbacks, wait for + * grace periods, and awaken followers, and the followers, which only + * invoke callbacks. Each leader is its own follower. The no-CBs CPUs + * do a wake_up() on their kthread when they insert a callback into any + * empty list, unless the rcu_nocb_poll boot parameter has been specified, + * in which case each kthread actively polls its CPU. (Which isn't so great + * for energy efficiency, but which does reduce RCU's overhead on that CPU.) * * This is intended to be used in conjunction with Frederic Weisbecker's * adaptive-idle work, which would seriously reduce OS jitter on CPUs * running CPU-bound user-mode computations. * - * Offloading of callback processing could also in theory be used as - * an energy-efficiency measure because CPUs with no RCU callbacks - * queued are more aggressive about entering dyntick-idle mode. + * Offloading of callbacks can also be used as an energy-efficiency + * measure because CPUs with no RCU callbacks queued are more aggressive + * about entering dyntick-idle mode. */ @@ -1976,10 +1978,7 @@ static void wake_nocb_leader_defer(struct rcu_data *rdp, int waketype, raw_spin_unlock_irqrestore(&rdp->nocb_lock, flags); } -/* - * Does the specified CPU need an RCU callback for this invocation - * of rcu_barrier()? - */ +/* Does rcu_barrier need to queue an RCU callback on the specified CPU? */ static bool rcu_nocb_cpu_needs_barrier(int cpu) { struct rcu_data *rdp = per_cpu_ptr(&rcu_data, cpu); @@ -1995,8 +1994,8 @@ static bool rcu_nocb_cpu_needs_barrier(int cpu) * callbacks would be posted. In the worst case, the first * barrier in rcu_barrier() suffices (but the caller cannot * necessarily rely on this, not a substitute for the caller - * getting the concurrency design right!). There must also be - * a barrier between the following load an posting of a callback + * getting the concurrency design right!). There must also be a + * barrier between the following load and posting of a callback * (if a callback is in fact needed). This is associated with an * atomic_inc() in the caller. */ -- 2.17.1