From: Peter Zijlstra <peterz@infradead.org>
To: Will Deacon <will.deacon@arm.com>
Cc: mingo@kernel.org, linux-kernel@vger.kernel.org,
longman@redhat.com, andrea.parri@amarulasolutions.com,
tglx@linutronix.de
Subject: Re: [RFC][PATCH 2/3] locking/qspinlock: Rework some comments
Date: Tue, 2 Oct 2018 15:43:58 +0200 [thread overview]
Message-ID: <20181002134358.GD26858@hirez.programming.kicks-ass.net> (raw)
In-Reply-To: <20181002132005.GE16422@arm.com>
On Tue, Oct 02, 2018 at 02:20:05PM +0100, Will Deacon wrote:
> > Ah, so the reason I write it like so is because when we get here,
> > val.locked_pending == 0, per the atomic_cond_read_acquire() condition.
>
> Ah, and I vaguely remember discussing this before. The way I read these
> transition diagrams, I find it most useful if they correspond to the lock
> word in memory. That way, it makes it clear about exactly which fields are
> stable, and which can be concurrently modified. So in the comment above,
> saying:
>
> *,*,0 -> *,*,1 : lock, contended
>
> is really helpful, because it clearly says "we're taking the lock, but the
> rest of the lock word could be modified by others at the same time", whereas
> saying:
>
> *,0,0 -> *,0,1 : lock, contended
>
> implies to me that pending is stable and cannot be set concurrently.
Fair enough, will restore.
next prev parent reply other threads:[~2018-10-02 13:44 UTC|newest]
Thread overview: 32+ messages / expand[flat|nested] mbox.gz Atom feed top
2018-09-26 11:01 [RFC][PATCH 0/3] locking/qspinlock: Improve determinism for x86 Peter Zijlstra
2018-09-26 11:01 ` [RFC][PATCH 1/3] locking/qspinlock: Re-order code Peter Zijlstra
2018-10-01 17:17 ` Will Deacon
2018-09-26 11:01 ` [RFC][PATCH 2/3] locking/qspinlock: Rework some comments Peter Zijlstra
2018-10-01 17:17 ` Will Deacon
2018-10-01 19:10 ` Peter Zijlstra
2018-10-02 13:20 ` Will Deacon
2018-10-02 13:43 ` Peter Zijlstra [this message]
2018-09-26 11:01 ` [RFC][PATCH 3/3] locking/qspinlock: Optimize for x86 Peter Zijlstra
2018-09-26 16:30 ` Waiman Long
2018-09-26 17:54 ` Peter Zijlstra
2018-09-27 7:29 ` Peter Zijlstra
2018-09-26 20:52 ` Andrea Parri
2018-09-27 7:17 ` Peter Zijlstra
2018-09-27 7:47 ` Andrea Parri
2018-09-27 7:59 ` Peter Zijlstra
2018-09-27 8:13 ` Andrea Parri
2018-09-27 8:57 ` Peter Zijlstra
2018-09-27 12:16 ` David Laight
2018-10-01 17:17 ` Will Deacon
2018-10-01 20:00 ` Peter Zijlstra
2018-10-02 13:19 ` Will Deacon
2018-10-02 14:14 ` Peter Zijlstra
2018-10-02 12:31 ` Andrea Parri
2018-10-02 13:22 ` Will Deacon
2018-10-02 13:44 ` Andrea Parri
2018-09-26 15:01 ` [RFC][PATCH 0/3] locking/qspinlock: Improve determinism " Sebastian Andrzej Siewior
2018-09-26 15:08 ` Thomas Gleixner
2018-09-26 15:38 ` Sebastian Andrzej Siewior
2018-09-26 16:20 ` Waiman Long
2018-09-26 17:51 ` Peter Zijlstra
2018-09-26 23:21 ` Waiman Long
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=20181002134358.GD26858@hirez.programming.kicks-ass.net \
--to=peterz@infradead.org \
--cc=andrea.parri@amarulasolutions.com \
--cc=linux-kernel@vger.kernel.org \
--cc=longman@redhat.com \
--cc=mingo@kernel.org \
--cc=tglx@linutronix.de \
--cc=will.deacon@arm.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).