From: Peter Zijlstra <peterz@infradead.org>
To: Davidlohr Bueso <dave@stgolabs.net>
Cc: mingo@kernel.org, will@kernel.org, oleg@redhat.com,
tglx@linutronix.de, linux-kernel@vger.kernel.org,
bigeasy@linutronix.de, juri.lelli@redhat.com,
williams@redhat.com, bristot@redhat.com, longman@redhat.com,
jack@suse.com
Subject: Re: [PATCH 5/5] locking/percpu-rwsem: Remove the embedded rwsem
Date: Tue, 17 Dec 2019 11:45:19 +0100 [thread overview]
Message-ID: <20191217104519.GD2844@hirez.programming.kicks-ass.net> (raw)
In-Reply-To: <20191118231935.7wvkozof3ocubxej@linux-p48b>
On Mon, Nov 18, 2019 at 03:19:35PM -0800, Davidlohr Bueso wrote:
> Similarly, afaict we can get rid of __percpu_up_read() and put the
> slowpath all into percpu_up_read(). Also explicitly mention the
> single task nature of the writer (which is a better comment for
> the rcuwait_wake_up()).
> static inline void percpu_down_read(struct percpu_rw_semaphore *sem)
> {
> @@ -103,10 +102,23 @@ static inline void percpu_up_read(struct percpu_rw_semaphore *sem)
> /*
> * Same as in percpu_down_read().
> */
> + if (likely(rcu_sync_is_idle(&sem->rss))) {
> __this_cpu_dec(*sem->read_count);
> + goto done;
> + }
> +
> + /*
> + * slowpath; reader will only ever wake a single blocked writer.
> + */
> + smp_mb(); /* B matches C */
> + /*
> + * In other words, if they see our decrement (presumably to
> + * aggregate zero, as that is the only time it matters) they
> + * will also see our critical section.
> + */
> + __this_cpu_dec(*sem->read_count);
> + rcuwait_wake_up(&sem->writer);
> +done:
> preempt_enable();
> }
Let me write that as a normal if () { } else { }.
But yes, that's small enough I suppose.
next prev parent reply other threads:[~2019-12-17 10:45 UTC|newest]
Thread overview: 23+ messages / expand[flat|nested] mbox.gz Atom feed top
2019-11-13 10:21 [PATCH 0/5] locking: Percpu-rwsem rewrite Peter Zijlstra
2019-11-13 10:21 ` [PATCH 1/5] locking/percpu-rwsem, lockdep: Make percpu-rwsem use its own lockdep_map Peter Zijlstra
2019-11-15 20:39 ` Davidlohr Bueso
2020-01-08 1:33 ` [PATCH] locking/percpu-rwsem: Add might_sleep() for writer locking Davidlohr Bueso
2020-01-08 1:33 ` Davidlohr Bueso
2020-02-11 12:48 ` [tip: locking/core] " tip-bot2 for Davidlohr Bueso
2019-11-13 10:21 ` [PATCH 2/5] locking/percpu-rwsem: Convert to bool Peter Zijlstra
2019-11-13 10:21 ` [PATCH 3/5] locking/percpu-rwsem: Move __this_cpu_inc() into the slowpath Peter Zijlstra
2019-11-13 10:21 ` [PATCH 4/5] locking/percpu-rwsem: Extract __percpu_down_read_trylock() Peter Zijlstra
2019-11-18 16:28 ` Oleg Nesterov
2019-11-13 10:21 ` [PATCH 5/5] locking/percpu-rwsem: Remove the embedded rwsem Peter Zijlstra
2019-11-18 19:53 ` Davidlohr Bueso
2019-11-18 23:19 ` Davidlohr Bueso
2019-12-17 10:45 ` Peter Zijlstra [this message]
2019-12-17 10:35 ` Peter Zijlstra
2019-11-18 21:52 ` Waiman Long
2019-12-17 10:28 ` Peter Zijlstra
2019-11-19 13:50 ` Waiman Long
2019-11-19 15:58 ` Oleg Nesterov
2019-11-19 16:28 ` Waiman Long
2019-12-17 10:26 ` Peter Zijlstra
2019-12-17 10:28 ` Peter Zijlstra
2019-11-15 17:14 ` [PATCH 0/5] locking: Percpu-rwsem rewrite Juri Lelli
Reply instructions:
You may reply publicly to this message via plain-text email
using any one of the following methods:
* Save the following mbox file, import it into your mail client,
and reply-to-all from there: mbox
Avoid top-posting and favor interleaved quoting:
https://en.wikipedia.org/wiki/Posting_style#Interleaved_style
* Reply using the --to, --cc, and --in-reply-to
switches of git-send-email(1):
git send-email \
--in-reply-to=20191217104519.GD2844@hirez.programming.kicks-ass.net \
--to=peterz@infradead.org \
--cc=bigeasy@linutronix.de \
--cc=bristot@redhat.com \
--cc=dave@stgolabs.net \
--cc=jack@suse.com \
--cc=juri.lelli@redhat.com \
--cc=linux-kernel@vger.kernel.org \
--cc=longman@redhat.com \
--cc=mingo@kernel.org \
--cc=oleg@redhat.com \
--cc=tglx@linutronix.de \
--cc=will@kernel.org \
--cc=williams@redhat.com \
/path/to/YOUR_REPLY
https://kernel.org/pub/software/scm/git/docs/git-send-email.html
* If your mail client supports setting the In-Reply-To header
via mailto: links, try the mailto: link
Be sure your reply has a Subject: header at the top and a blank line
before the message body.
This is a public inbox, see mirroring instructions
for how to clone and mirror all data and code used for this inbox;
as well as URLs for NNTP newsgroup(s).