From: "Paul E. McKenney" <paulmck@kernel.org>
To: John Ogness <john.ogness@linutronix.de>
Cc: rcu@vger.kernel.org, linux-kernel@vger.kernel.org,
kernel-team@fb.com, rostedt@goodmis.org,
Thomas Gleixner <tglx@linutronix.de>,
Petr Mladek <pmladek@suse.com>
Subject: Re: [PATCH RFC v2 rcu 1/8] srcu: Convert ->srcu_lock_count and ->srcu_unlock_count to atomic
Date: Fri, 30 Sep 2022 08:35:06 -0700 [thread overview]
Message-ID: <20220930153506.GD4196@paulmck-ThinkPad-P17-Gen-1> (raw)
In-Reply-To: <87ill4vrb9.fsf@jogness.linutronix.de>
On Fri, Sep 30, 2022 at 05:08:18PM +0206, John Ogness wrote:
> Hi Paul,
>
> On 2022-09-29, "Paul E. McKenney" <paulmck@kernel.org> wrote:
> > diff --git a/kernel/rcu/srcutree.c b/kernel/rcu/srcutree.c
> > index 1c304fec89c0..6fd0665f4d1f 100644
> > --- a/kernel/rcu/srcutree.c
> > +++ b/kernel/rcu/srcutree.c
> > @@ -636,7 +636,7 @@ int __srcu_read_lock(struct srcu_struct *ssp)
> > int idx;
> >
> > idx = READ_ONCE(ssp->srcu_idx) & 0x1;
> > - this_cpu_inc(ssp->sda->srcu_lock_count[idx]);
> > + this_cpu_inc(ssp->sda->srcu_lock_count[idx].counter);
> > smp_mb(); /* B */ /* Avoid leaking the critical section. */
> > return idx;
> > }
>
> Is there any particular reason that you are directly modifying @counter
> instead of raw_cpu_ptr()+atomic_long_inc() that do you in
> __srcu_read_lock_nmisafe() of patch 2?
Performance. From what I can see, this_cpu_inc() is way faster than
atomic_long_inc() on x86 and s390. Maybe also on loongarch. No idea
on arm64.
> > @@ -650,7 +650,7 @@ EXPORT_SYMBOL_GPL(__srcu_read_lock);
> > void __srcu_read_unlock(struct srcu_struct *ssp, int idx)
> > {
> > smp_mb(); /* C */ /* Avoid leaking the critical section. */
> > - this_cpu_inc(ssp->sda->srcu_unlock_count[idx]);
> > + this_cpu_inc(ssp->sda->srcu_unlock_count[idx].counter);
> > }
> > EXPORT_SYMBOL_GPL(__srcu_read_unlock);
>
> Ditto.
Ditto back at you! ;-)
> > @@ -1687,8 +1687,8 @@ void srcu_torture_stats_print(struct srcu_struct *ssp, char *tt, char *tf)
> > struct srcu_data *sdp;
> >
> > sdp = per_cpu_ptr(ssp->sda, cpu);
> > - u0 = data_race(sdp->srcu_unlock_count[!idx]);
> > - u1 = data_race(sdp->srcu_unlock_count[idx]);
> > + u0 = data_race(sdp->srcu_unlock_count[!idx].counter);
> > + u1 = data_race(sdp->srcu_unlock_count[idx].counter);
> >
> > /*
> > * Make sure that a lock is always counted if the corresponding
>
> And instead of atomic_long_read().
You are right, here I could just as well use atomic_long_read().
> > @@ -1696,8 +1696,8 @@ void srcu_torture_stats_print(struct srcu_struct *ssp, char *tt, char *tf)
> > */
> > smp_rmb();
> >
> > - l0 = data_race(sdp->srcu_lock_count[!idx]);
> > - l1 = data_race(sdp->srcu_lock_count[idx]);
> > + l0 = data_race(sdp->srcu_lock_count[!idx].counter);
> > + l1 = data_race(sdp->srcu_lock_count[idx].counter);
> >
> > c0 = l0 - u0;
> > c1 = l1 - u1;
>
> Ditto.
And here as well. ;-)
I will fix these, and thank you for looking this over!
Thanx, Paul
next prev parent reply other threads:[~2022-09-30 15:35 UTC|newest]
Thread overview: 60+ messages / expand[flat|nested] mbox.gz Atom feed top
2022-09-21 14:46 [PATCH rcu 0/4] NMI-safe SRCU reader API Paul E. McKenney
2022-09-21 14:46 ` [PATCH RFC rcu 1/4] srcu: Convert ->srcu_lock_count and ->srcu_unlock_count to atomic Paul E. McKenney
2022-09-21 14:46 ` [PATCH RFC rcu 2/4] srcu: Create and srcu_read_lock_nmisafe() and srcu_read_unlock_nmisafe() Paul E. McKenney
2022-09-21 14:46 ` [PATCH RFC rcu 3/4] srcu: Check for consistent per-CPU per-srcu_struct NMI safety Paul E. McKenney
2022-09-21 14:46 ` [PATCH RFC rcu 4/4] srcu: Check for consistent global " Paul E. McKenney
2022-09-29 18:07 ` [PATCH v2 rcu 0/8] NMI-safe SRCU reader API Paul E. McKenney
2022-09-29 18:07 ` [PATCH RFC v2 rcu 1/8] srcu: Convert ->srcu_lock_count and ->srcu_unlock_count to atomic Paul E. McKenney
2022-09-30 15:02 ` John Ogness
2022-09-30 15:35 ` Paul E. McKenney [this message]
2022-09-30 20:37 ` John Ogness
2022-10-01 16:51 ` Paul E. McKenney
2022-09-29 18:07 ` [PATCH RFC v2 rcu 2/8] srcu: Create an srcu_read_lock_nmisafe() and srcu_read_unlock_nmisafe() Paul E. McKenney
2022-10-02 15:55 ` Frederic Weisbecker
2022-10-02 15:57 ` Frederic Weisbecker
2022-10-02 16:10 ` Paul E. McKenney
2022-10-02 16:09 ` Paul E. McKenney
2022-10-02 21:47 ` Frederic Weisbecker
2022-10-02 23:46 ` Paul E. McKenney
2022-10-03 9:55 ` Frederic Weisbecker
2022-10-03 11:52 ` Paul E. McKenney
2022-10-18 14:31 ` John Ogness
2022-10-18 15:18 ` Paul E. McKenney
2022-09-29 18:07 ` [PATCH RFC v2 rcu 3/8] srcu: Check for consistent per-CPU per-srcu_struct NMI safety Paul E. McKenney
2022-10-02 22:06 ` Frederic Weisbecker
2022-10-02 23:51 ` Paul E. McKenney
2022-10-03 10:13 ` Frederic Weisbecker
2022-10-03 11:57 ` Paul E. McKenney
2022-10-03 12:37 ` Frederic Weisbecker
2022-10-03 13:32 ` Paul E. McKenney
2022-10-03 13:36 ` Frederic Weisbecker
2022-09-29 18:07 ` [PATCH RFC v2 rcu 4/8] srcu: Check for consistent global " Paul E. McKenney
2022-09-29 18:07 ` [PATCH RFC v2 rcu 5/8] arch/x86: Add ARCH_HAS_NMI_SAFE_THIS_CPU_OPS Kconfig option Paul E. McKenney
2022-09-29 18:07 ` [PATCH RFC v2 rcu 6/8] arch/arm64: " Paul E. McKenney
2022-10-05 11:12 ` Mark Rutland
2022-09-29 18:07 ` [PATCH RFC v2 rcu 7/8] arch/loongarch: " Paul E. McKenney
2022-09-29 18:07 ` [PATCH RFC v2 rcu 8/8] arch/s390: " Paul E. McKenney
2022-10-03 14:11 ` [PATCH v2 rcu 0/8] NMI-safe SRCU reader API Frederic Weisbecker
2022-10-03 16:38 ` Paul E. McKenney
2022-10-14 22:47 ` Joel Fernandes
2022-10-14 22:52 ` Joel Fernandes
2022-10-18 10:33 ` John Ogness
2022-10-18 15:24 ` Paul E. McKenney
2022-10-18 18:44 ` John Ogness
2022-10-18 18:59 ` Paul E. McKenney
2022-10-18 21:57 ` Paul E. McKenney
2022-10-19 11:13 ` John Ogness
2022-10-19 19:14 ` Paul E. McKenney
2022-10-19 21:38 ` John Ogness
2022-10-19 22:05 ` Frederic Weisbecker
2022-10-20 22:27 ` Paul E. McKenney
2022-10-20 22:41 ` Paul E. McKenney
2022-10-21 12:27 ` John Ogness
2022-10-21 13:59 ` Paul E. McKenney
2022-10-21 18:41 ` Paul E. McKenney
2022-10-24 6:15 ` John Ogness
2022-10-24 13:47 ` Paul E. McKenney
2022-10-27 9:31 ` John Ogness
2022-10-27 14:10 ` Paul E. McKenney
2022-10-27 14:39 ` John Ogness
2022-10-27 16:01 ` Paul E. McKenney
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