From: "Paul E. McKenney" <paulmck@kernel.org>
To: Neeraj Upadhyay <neeraju@codeaurora.org>
Cc: rcu@vger.kernel.org, linux-kernel@vger.kernel.org,
kernel-team@fb.com, mingo@kernel.org, jiangshanlai@gmail.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
Subject: Re: [PATCH RFC tip/core/rcu 3/5] srcu: Provide internal interface to start a Tree SRCU grace period
Date: Fri, 20 Nov 2020 16:37:20 -0800 [thread overview]
Message-ID: <20201121003720.GQ1437@paulmck-ThinkPad-P72> (raw)
In-Reply-To: <69c05cd0-8187-49a7-5b2d-1a10ba42fa44@codeaurora.org>
On Fri, Nov 20, 2020 at 05:06:50PM +0530, Neeraj Upadhyay wrote:
>
>
> On 11/17/2020 6:10 AM, paulmck@kernel.org wrote:
> > From: "Paul E. McKenney" <paulmck@kernel.org>
> >
> > There is a need for a polling interface for SRCU grace periods.
> > This polling needs to initiate an SRCU grace period without having
> > to queue (and manage) a callback. This commit therefore splits the
> > Tree SRCU __call_srcu() function into callback-initialization and
> > queuing/start-grace-period portions, with the latter in a new function
> > named srcu_gp_start_if_needed(). This function may be passed a NULL
> > callback pointer, in which case it will refrain from queuing anything.
> >
> > Why have the new function mess with queuing? Locking considerations,
> > of course!
> >
> > Link: https://lore.kernel.org/rcu/20201112201547.GF3365678@moria.home.lan/
> > Reported-by: Kent Overstreet <kent.overstreet@gmail.com>
> > Signed-off-by: Paul E. McKenney <paulmck@kernel.org>
> > ---
>
> Reviewed-by: Neeraj Upadhyay <neeraju@codeaurora.org>
I applied both Reviewed-bys, thank you!
Thanx, Paul
> Thanks
> Neeraj
>
> > kernel/rcu/srcutree.c | 66 +++++++++++++++++++++++++++++----------------------
> > 1 file changed, 37 insertions(+), 29 deletions(-)
> >
> > diff --git a/kernel/rcu/srcutree.c b/kernel/rcu/srcutree.c
> > index 79b7081..d930ece 100644
> > --- a/kernel/rcu/srcutree.c
> > +++ b/kernel/rcu/srcutree.c
> > @@ -808,6 +808,42 @@ static void srcu_leak_callback(struct rcu_head *rhp)
> > }
> > /*
> > + * Start an SRCU grace period, and also queue the callback if non-NULL.
> > + */
> > +static void srcu_gp_start_if_needed(struct srcu_struct *ssp, struct rcu_head *rhp, bool do_norm)
> > +{
> > + unsigned long flags;
> > + int idx;
> > + bool needexp = false;
> > + bool needgp = false;
> > + unsigned long s;
> > + struct srcu_data *sdp;
> > +
> > + idx = srcu_read_lock(ssp);
> > + sdp = raw_cpu_ptr(ssp->sda);
> > + spin_lock_irqsave_rcu_node(sdp, flags);
> > + rcu_segcblist_enqueue(&sdp->srcu_cblist, rhp);
> > + rcu_segcblist_advance(&sdp->srcu_cblist,
> > + rcu_seq_current(&ssp->srcu_gp_seq));
> > + s = rcu_seq_snap(&ssp->srcu_gp_seq);
> > + (void)rcu_segcblist_accelerate(&sdp->srcu_cblist, s);
> > + if (ULONG_CMP_LT(sdp->srcu_gp_seq_needed, s)) {
> > + sdp->srcu_gp_seq_needed = s;
> > + needgp = true;
> > + }
> > + if (!do_norm && ULONG_CMP_LT(sdp->srcu_gp_seq_needed_exp, s)) {
> > + sdp->srcu_gp_seq_needed_exp = s;
> > + needexp = true;
> > + }
> > + spin_unlock_irqrestore_rcu_node(sdp, flags);
> > + if (needgp)
> > + srcu_funnel_gp_start(ssp, sdp, s, do_norm);
> > + else if (needexp)
> > + srcu_funnel_exp_start(ssp, sdp->mynode, s);
> > + srcu_read_unlock(ssp, idx);
> > +}
> > +
> > +/*
> > * Enqueue an SRCU callback on the srcu_data structure associated with
> > * the current CPU and the specified srcu_struct structure, initiating
> > * grace-period processing if it is not already running.
> > @@ -838,13 +874,6 @@ static void srcu_leak_callback(struct rcu_head *rhp)
> > static void __call_srcu(struct srcu_struct *ssp, struct rcu_head *rhp,
> > rcu_callback_t func, bool do_norm)
> > {
> > - unsigned long flags;
> > - int idx;
> > - bool needexp = false;
> > - bool needgp = false;
> > - unsigned long s;
> > - struct srcu_data *sdp;
> > -
> > check_init_srcu_struct(ssp);
> > if (debug_rcu_head_queue(rhp)) {
> > /* Probable double call_srcu(), so leak the callback. */
> > @@ -853,28 +882,7 @@ static void __call_srcu(struct srcu_struct *ssp, struct rcu_head *rhp,
> > return;
> > }
> > rhp->func = func;
> > - idx = srcu_read_lock(ssp);
> > - sdp = raw_cpu_ptr(ssp->sda);
> > - spin_lock_irqsave_rcu_node(sdp, flags);
> > - rcu_segcblist_enqueue(&sdp->srcu_cblist, rhp);
> > - rcu_segcblist_advance(&sdp->srcu_cblist,
> > - rcu_seq_current(&ssp->srcu_gp_seq));
> > - s = rcu_seq_snap(&ssp->srcu_gp_seq);
> > - (void)rcu_segcblist_accelerate(&sdp->srcu_cblist, s);
> > - if (ULONG_CMP_LT(sdp->srcu_gp_seq_needed, s)) {
> > - sdp->srcu_gp_seq_needed = s;
> > - needgp = true;
> > - }
> > - if (!do_norm && ULONG_CMP_LT(sdp->srcu_gp_seq_needed_exp, s)) {
> > - sdp->srcu_gp_seq_needed_exp = s;
> > - needexp = true;
> > - }
> > - spin_unlock_irqrestore_rcu_node(sdp, flags);
> > - if (needgp)
> > - srcu_funnel_gp_start(ssp, sdp, s, do_norm);
> > - else if (needexp)
> > - srcu_funnel_exp_start(ssp, sdp->mynode, s);
> > - srcu_read_unlock(ssp, idx);
> > + srcu_gp_start_if_needed(ssp, rhp, do_norm);
> > }
> > /**
> >
>
> --
> QUALCOMM INDIA, on behalf of Qualcomm Innovation Center, Inc. is a member of
> the Code Aurora Forum, hosted by The Linux Foundation
next prev parent reply other threads:[~2020-11-21 0:37 UTC|newest]
Thread overview: 23+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-11-17 0:40 [PATCH tip/core/rcu 0/5] Provide SRCU polling grace-period interfaces Paul E. McKenney
2020-11-17 0:40 ` [PATCH RFC tip/core/rcu 1/5] srcu: Make Tiny SRCU use multi-bit grace-period counter paulmck
2020-11-19 8:14 ` Neeraj Upadhyay
2020-11-19 18:00 ` Paul E. McKenney
2020-11-17 0:40 ` [PATCH RFC tip/core/rcu 2/5] srcu: Provide internal interface to start a Tiny SRCU grace period paulmck
2020-11-20 11:36 ` Neeraj Upadhyay
2020-11-17 0:40 ` [PATCH RFC tip/core/rcu 3/5] srcu: Provide internal interface to start a Tree " paulmck
2020-11-20 11:36 ` Neeraj Upadhyay
2020-11-21 0:37 ` Paul E. McKenney [this message]
2020-11-17 0:40 ` [PATCH RFC tip/core/rcu 4/5] srcu: Provide polling interfaces for Tiny SRCU grace periods paulmck
2020-11-20 11:58 ` Neeraj Upadhyay
2020-11-21 0:13 ` Paul E. McKenney
2020-11-22 14:27 ` Neeraj Upadhyay
2020-11-22 18:01 ` Paul E. McKenney
2020-11-23 4:34 ` Neeraj Upadhyay
2020-11-23 21:07 ` Paul E. McKenney
2020-11-17 0:40 ` [PATCH RFC tip/core/rcu 5/5] srcu: Provide polling interfaces for Tree " paulmck
2020-11-20 12:01 ` Neeraj Upadhyay
2020-11-21 0:16 ` Paul E. McKenney
2020-11-22 14:22 ` Neeraj Upadhyay
2020-11-21 0:58 ` [PATCH tip/core/rcu 0/5] Provide SRCU polling grace-period interfaces Paul E. McKenney
2020-11-21 1:05 ` Steven Rostedt
2020-11-21 1:12 ` Paul E. McKenney
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