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McKenney" To: Steven Rostedt Cc: linux-kernel@vger.kernel.org, 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, dhowells@redhat.com, edumazet@google.com, fweisbec@gmail.com, oleg@redhat.com, joel@joelfernandes.org, Byungchul Park Subject: Re: [PATCH tip/core/rcu 01/19] rcu: Refactor rcu_{nmi,irq}_{enter,exit}() Reply-To: paulmck@linux.vnet.ibm.com References: <20180829222021.GA29944@linux.vnet.ibm.com> <20180829222047.319-1-paulmck@linux.vnet.ibm.com> <20180830141032.76efd12c@gandalf.local.home> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20180830141032.76efd12c@gandalf.local.home> User-Agent: Mutt/1.5.21 (2010-09-15) X-TM-AS-GCONF: 00 x-cbid: 18083023-0072-0000-0000-0000039A22E3 X-IBM-SpamModules-Scores: X-IBM-SpamModules-Versions: BY=3.00009641; HX=3.00000242; KW=3.00000007; PH=3.00000004; SC=3.00000266; SDB=6.01081231; UDB=6.00557790; IPR=6.00861216; MB=3.00023023; MTD=3.00000008; XFM=3.00000015; UTC=2018-08-30 23:02:08 X-IBM-AV-DETECTION: SAVI=unused REMOTE=unused XFE=unused x-cbparentid: 18083023-0073-0000-0000-00004941BC21 Message-Id: <20180830230205.GV4225@linux.vnet.ibm.com> X-Proofpoint-Virus-Version: vendor=fsecure engine=2.50.10434:,, definitions=2018-08-30_08:,, signatures=0 X-Proofpoint-Spam-Details: rule=outbound_notspam policy=outbound score=0 priorityscore=1501 malwarescore=0 suspectscore=0 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=8.0.1-1807170000 definitions=main-1808300229 Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Thu, Aug 30, 2018 at 02:10:32PM -0400, Steven Rostedt wrote: > On Wed, 29 Aug 2018 15:20:29 -0700 > "Paul E. McKenney" wrote: > > > This commit also changes order of execution from this: > > > > rcu_dynticks_task_exit(); > > rcu_dynticks_eqs_exit(); > > trace_rcu_dyntick(); > > rcu_cleanup_after_idle(); > > > > To this: > > > > rcu_dynticks_task_exit(); > > rcu_dynticks_eqs_exit(); > > rcu_cleanup_after_idle(); > > trace_rcu_dyntick(); > > > > In other words, the calls to trace_rcu_dyntick() and trace_rcu_dyntick() > > How is trace_rcu_dyntick() and trace_rcu_dyntick reversed ? ;-) Very carefully? I changed the first trace_rcu_dyntick() to rcu_cleanup_after_idle(), good catch! > > are reversed. This has no functional effect because the real > > concern is whether a given call is before or after the call to > > rcu_dynticks_eqs_exit(), and this patch does not change that. Before the > > call to rcu_dynticks_eqs_exit(), RCU is not yet watching the current > > CPU and after that call RCU is watching. > > > > A similar switch in calling order happens on the idle-entry path, with > > similar lack of effect for the same reasons. > > > > Suggested-by: Paul E. McKenney > > Signed-off-by: Byungchul Park > > Signed-off-by: Paul E. McKenney > > --- > > kernel/rcu/tree.c | 61 +++++++++++++++++++++++++++++++---------------- > > 1 file changed, 41 insertions(+), 20 deletions(-) > > > > diff --git a/kernel/rcu/tree.c b/kernel/rcu/tree.c > > index 0b760c1369f7..0adf77923e8b 100644 > > --- a/kernel/rcu/tree.c > > +++ b/kernel/rcu/tree.c > > @@ -771,17 +771,18 @@ void rcu_user_enter(void) > > #endif /* CONFIG_NO_HZ_FULL */ > > > > /** > > - * rcu_nmi_exit - inform RCU of exit from NMI context > > + * rcu_nmi_exit_common - inform RCU of exit from NMI context > > + * @irq: Is this call from rcu_irq_exit? > > * > > * If we are returning from the outermost NMI handler that interrupted an > > * RCU-idle period, update rdtp->dynticks and rdtp->dynticks_nmi_nesting > > * to let the RCU grace-period handling know that the CPU is back to > > * being RCU-idle. > > * > > - * If you add or remove a call to rcu_nmi_exit(), be sure to test > > + * If you add or remove a call to rcu_nmi_exit_common(), be sure to test > > * with CONFIG_RCU_EQS_DEBUG=y. > > As this is a static function, this description doesn't make sense. You > need to move the description down to the new rcu_nmi_exit() below. Heh! This will give git a chance to show off its conflict-resolution capabilities!!! Let's see how it does... Not bad! It resolved the conflicts automatically despite the code movement. Nice!!! ;-) > Other than that... > > Reviewed-by: Steven Rostedt (VMware) Of course my penalty for my lack of faith in git is a second rebase to pull this in. ;-) Thank you for your review and comments! Thanx, Paul > -- Steve > > > > */ > > -void rcu_nmi_exit(void) > > +static __always_inline void rcu_nmi_exit_common(bool irq) > > { > > struct rcu_dynticks *rdtp = this_cpu_ptr(&rcu_dynticks); > > > > @@ -807,7 +808,22 @@ void rcu_nmi_exit(void) > > /* This NMI interrupted an RCU-idle CPU, restore RCU-idleness. */ > > trace_rcu_dyntick(TPS("Startirq"), rdtp->dynticks_nmi_nesting, 0, rdtp->dynticks); > > WRITE_ONCE(rdtp->dynticks_nmi_nesting, 0); /* Avoid store tearing. */ > > + > > + if (irq) > > + rcu_prepare_for_idle(); > > + > > rcu_dynticks_eqs_enter(); > > + > > + if (irq) > > + rcu_dynticks_task_enter(); > > +} > > + > > +/** > > + * rcu_nmi_exit - inform RCU of exit from NMI context > > + */ > > +void rcu_nmi_exit(void) > > +{ > > + rcu_nmi_exit_common(false); > > } > > > > /** > > @@ -831,14 +847,8 @@ void rcu_nmi_exit(void) > > */ > > void rcu_irq_exit(void) > > { > > - struct rcu_dynticks *rdtp = this_cpu_ptr(&rcu_dynticks); > > - > > lockdep_assert_irqs_disabled(); > > - if (rdtp->dynticks_nmi_nesting == 1) > > - rcu_prepare_for_idle(); > > - rcu_nmi_exit(); > > - if (rdtp->dynticks_nmi_nesting == 0) > > - rcu_dynticks_task_enter(); > > + rcu_nmi_exit_common(true); > > } > > > > /* > > @@ -921,7 +931,8 @@ void rcu_user_exit(void) > > #endif /* CONFIG_NO_HZ_FULL */ > > > > /** > > - * rcu_nmi_enter - inform RCU of entry to NMI context > > + * rcu_nmi_enter_common - inform RCU of entry to NMI context > > + * @irq: Is this call from rcu_irq_enter? > > * > > * If the CPU was idle from RCU's viewpoint, update rdtp->dynticks and > > * rdtp->dynticks_nmi_nesting to let the RCU grace-period handling know > > @@ -929,10 +940,10 @@ void rcu_user_exit(void) > > * long as the nesting level does not overflow an int. (You will probably > > * run out of stack space first.) > > * > > - * If you add or remove a call to rcu_nmi_enter(), be sure to test > > + * If you add or remove a call to rcu_nmi_enter_common(), be sure to test > > * with CONFIG_RCU_EQS_DEBUG=y. > > */ > > -void rcu_nmi_enter(void) > > +static __always_inline void rcu_nmi_enter_common(bool irq) > > { > > struct rcu_dynticks *rdtp = this_cpu_ptr(&rcu_dynticks); > > long incby = 2; > > @@ -949,7 +960,15 @@ void rcu_nmi_enter(void) > > * period (observation due to Andy Lutomirski). > > */ > > if (rcu_dynticks_curr_cpu_in_eqs()) { > > + > > + if (irq) > > + rcu_dynticks_task_exit(); > > + > > rcu_dynticks_eqs_exit(); > > + > > + if (irq) > > + rcu_cleanup_after_idle(); > > + > > incby = 1; > > } > > trace_rcu_dyntick(incby == 1 ? TPS("Endirq") : TPS("++="), > > @@ -960,6 +979,14 @@ void rcu_nmi_enter(void) > > barrier(); > > } > > > > +/** > > + * rcu_nmi_enter - inform RCU of entry to NMI context > > + */ > > +void rcu_nmi_enter(void) > > +{ > > + rcu_nmi_enter_common(false); > > +} > > + > > /** > > * rcu_irq_enter - inform RCU that current CPU is entering irq away from idle > > * > > @@ -984,14 +1011,8 @@ void rcu_nmi_enter(void) > > */ > > void rcu_irq_enter(void) > > { > > - struct rcu_dynticks *rdtp = this_cpu_ptr(&rcu_dynticks); > > - > > lockdep_assert_irqs_disabled(); > > - if (rdtp->dynticks_nmi_nesting == 0) > > - rcu_dynticks_task_exit(); > > - rcu_nmi_enter(); > > - if (rdtp->dynticks_nmi_nesting == 1) > > - rcu_cleanup_after_idle(); > > + rcu_nmi_enter_common(true); > > } > > > > /* >