From: Oleg Nesterov <oleg@redhat.com>
To: Peter Zijlstra <peterz@infradead.org>
Cc: Will Deacon <will.deacon@kernel.org>,
Ingo Molnar <mingo@kernel.org>,
Thomas Gleixner <tglx@linutronix.de>,
linux-kernel@vger.kernel.org, bigeasy@linutronix.de,
juri.lelli@redhat.com, williams@redhat.com, bristot@redhat.com,
longman@redhat.com, dave@stgolabs.net, jack@suse.com
Subject: Re: [PATCH] locking/percpu_rwsem: Rewrite to not use rwsem
Date: Wed, 30 Oct 2019 15:21:10 +0100 [thread overview]
Message-ID: <20191030142110.GA17800@redhat.com> (raw)
In-Reply-To: <20191029184739.GA3079@worktop.programming.kicks-ass.net>
On 10/29, Peter Zijlstra wrote:
>
> I like that symmetry, but see below ...
...
> > void __percpu_up_read(struct percpu_rw_semaphore *sem)
> > {
> > smp_mb();
> >
> > __this_cpu_dec(*sem->read_count);
> >
> preempt_enable();
> > wake_up(&sem->waiters);
> preempt_disable()
>
> and this (sadly) means there's a bunch of back-to-back
> preempt_disable()+preempt_enable() calls.
Hmm. Where did these enable+disable come from?
void __percpu_up_read(struct percpu_rw_semaphore *sem)
{
smp_mb();
__this_cpu_dec(*sem->read_count);
wake_up(&sem->waiters);
}
should work just fine?
Oleg.
next prev parent reply other threads:[~2019-10-30 14:21 UTC|newest]
Thread overview: 19+ messages / expand[flat|nested] mbox.gz Atom feed top
2019-08-05 14:02 [PATCH] locking/percpu_rwsem: Rewrite to not use rwsem Peter Zijlstra
2019-08-05 14:43 ` Boqun Feng
2019-08-05 14:58 ` Boqun Feng
2019-08-05 15:43 ` Peter Zijlstra
2019-08-06 14:15 ` Boqun Feng
2019-08-06 16:17 ` Oleg Nesterov
2019-08-06 17:15 ` Peter Zijlstra
2019-08-07 9:56 ` Oleg Nesterov
2019-10-29 18:47 ` Peter Zijlstra
2019-10-30 14:21 ` Oleg Nesterov [this message]
2019-10-30 16:09 ` Peter Zijlstra
2019-10-30 17:52 ` Peter Zijlstra
2019-10-30 18:47 ` Peter Zijlstra
2019-10-30 19:31 ` Peter Zijlstra
2019-10-31 6:11 ` Peter Zijlstra
2019-08-07 14:45 ` Will Deacon
2019-10-29 19:06 ` Peter Zijlstra
2019-10-30 15:57 ` Oleg Nesterov
2019-10-30 16:47 ` Peter Zijlstra
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