From: Will Deacon <will.deacon@arm.com>
To: Alan Stern <stern@rowland.harvard.edu>
Cc: Andrea Parri <parri.andrea@gmail.com>,
"Paul E. McKenney" <paulmck@linux.vnet.ibm.com>,
linux-kernel@vger.kernel.org, linux-arch@vger.kernel.org,
mingo@kernel.org, peterz@infradead.org, boqun.feng@gmail.com,
npiggin@gmail.com, dhowells@redhat.com, j.alglave@ucl.ac.uk,
luc.maranget@inria.fr, akiyks@gmail.com
Subject: Re: [PATCH RFC LKMM 1/7] tools/memory-model: Add extra ordering for locks and remove it for ordinary release/acquire
Date: Fri, 31 Aug 2018 17:06:40 +0100 [thread overview]
Message-ID: <20180831160640.GG30626@arm.com> (raw)
In-Reply-To: <Pine.LNX.4.44L0.1808311042340.4901-100000@netrider.rowland.org>
On Fri, Aug 31, 2018 at 10:52:54AM -0400, Alan Stern wrote:
> On Fri, 31 Aug 2018, Andrea Parri wrote:
> > On Thu, Aug 30, 2018 at 05:31:32PM -0400, Alan Stern wrote:
> > > On Thu, 30 Aug 2018, Andrea Parri wrote:
> > > > (Remark: ordinary release/acquire are building blocks for code such as
> > > > qspinlock, (q)rwlock, mutex, rwsem, ... and what else??).
> > >
> > > But are these building blocks used the same way for all architectures?
> >
> > The more, the better! (because then we have the LKMM tools)
> >
> > We already discussed the "fast path" example: the fast paths of the
> > above all resemble:
> >
> > *_lock(s): atomic_cmpxchg_acquire(&s->val, UNLOCKED_VAL, LOCKED_VAL) ...
> > *_unlock(s): ... atomic_set_release(&s->val, UNLOCKED_VAL)
> >
> > When I read this code, I think "Of course." (unless some arch. has
> > messed the implementation of cmpxchg_* up, which can happen...); but
> > then I read the subject line of this patch and I think "Wait, what?".
> >
> > You can argue that this is not generic code, sure; but why on Earth
> > would you like to do so?!
>
> Because the code might not work! On RISC-V, for example, the
> implementation of ordinary release/acquire is currently not as strong
> as atomic release/acquire.
>
> Yes, it's true that implementing locks with atomic_cmpxchg_acquire
> should be correct on all existing architectures. And Paul has invited
> a patch to modify the LKMM accordingly. If you feel that such a change
> would be a useful enhancement to the LKMM's applicability, please write
> it.
Yes, please! That would be the "RmW" discussion which Andrea partially
quoted earlier on, so getting that going independently from this patch
sounds like a great idea to me.
Cheers,
Will
next prev parent reply other threads:[~2018-08-31 16:06 UTC|newest]
Thread overview: 112+ messages / expand[flat|nested] mbox.gz Atom feed top
2018-08-29 21:10 [PATCH RFC memory-model 0/7] Memory-model changes Paul E. McKenney
2018-08-29 21:10 ` Paul E. McKenney
2018-08-29 21:10 ` [PATCH RFC LKMM 1/7] tools/memory-model: Add extra ordering for locks and remove it for ordinary release/acquire Paul E. McKenney
2018-08-29 21:10 ` Paul E. McKenney
2018-08-30 12:50 ` Andrea Parri
2018-08-30 12:50 ` Andrea Parri
2018-08-30 21:31 ` Alan Stern
2018-08-30 21:31 ` Alan Stern
2018-08-31 9:17 ` Andrea Parri
2018-08-31 9:17 ` Andrea Parri
2018-08-31 14:52 ` Alan Stern
2018-08-31 14:52 ` Alan Stern
2018-08-31 16:06 ` Will Deacon [this message]
2018-08-31 16:06 ` Will Deacon
2018-08-31 18:28 ` Andrea Parri
2018-08-31 18:28 ` Andrea Parri
2018-09-03 9:01 ` Andrea Parri
2018-09-03 9:01 ` Andrea Parri
2018-09-03 17:04 ` Will Deacon
2018-09-03 17:04 ` Will Deacon
2018-09-04 8:11 ` Andrea Parri
2018-09-04 8:11 ` Andrea Parri
2018-09-04 19:09 ` Alan Stern
2018-09-04 19:09 ` Alan Stern
2018-09-05 7:21 ` Andrea Parri
2018-09-05 7:21 ` Andrea Parri
2018-09-05 14:33 ` Akira Yokosawa
2018-09-05 14:33 ` Akira Yokosawa
2018-09-05 14:53 ` Paul E. McKenney
2018-09-05 14:53 ` Paul E. McKenney
2018-09-05 15:00 ` Andrea Parri
2018-09-05 15:00 ` Andrea Parri
2018-09-05 15:04 ` Akira Yokosawa
2018-09-05 15:04 ` Akira Yokosawa
2018-09-05 15:24 ` Andrea Parri
2018-09-05 15:24 ` Andrea Parri
2018-09-03 17:52 ` Alan Stern
2018-09-03 17:52 ` Alan Stern
2018-09-03 18:28 ` Andrea Parri
2018-09-03 18:28 ` Andrea Parri
2018-09-06 1:25 ` Alan Stern
2018-09-06 1:25 ` Alan Stern
2018-09-06 9:36 ` Andrea Parri
2018-09-06 9:36 ` Andrea Parri
2018-09-07 16:00 ` Alan Stern
2018-09-07 16:00 ` Alan Stern
2018-09-07 16:09 ` Will Deacon
2018-09-07 16:09 ` Will Deacon
2018-09-07 16:39 ` Daniel Lustig
2018-09-07 16:39 ` Daniel Lustig
2018-09-07 17:38 ` Alan Stern
2018-09-07 17:38 ` Alan Stern
2018-09-08 0:04 ` Daniel Lustig
2018-09-08 0:04 ` Daniel Lustig
2018-09-08 9:58 ` Andrea Parri
2018-09-08 9:58 ` Andrea Parri
2018-09-11 19:31 ` Alan Stern
2018-09-11 19:31 ` Alan Stern
2018-09-11 20:03 ` Paul E. McKenney
2018-09-11 20:03 ` Paul E. McKenney
2018-09-12 14:24 ` Alan Stern
2018-09-12 14:24 ` Alan Stern
2018-09-13 17:07 ` Alan Stern
2018-09-13 17:07 ` Alan Stern
2018-09-14 14:37 ` Andrea Parri
2018-09-14 14:37 ` Andrea Parri
2018-09-14 16:29 ` Alan Stern
2018-09-14 16:29 ` Alan Stern
2018-09-14 19:44 ` Andrea Parri
2018-09-14 19:44 ` Andrea Parri
2018-09-14 21:08 ` [PATCH v5] " Alan Stern
2018-09-14 21:08 ` Alan Stern
2018-09-15 3:56 ` Paul E. McKenney
2018-09-15 3:56 ` Paul E. McKenney
2018-09-03 17:05 ` [PATCH RFC LKMM 1/7] " Will Deacon
2018-09-03 17:05 ` Will Deacon
2018-08-31 17:55 ` Andrea Parri
2018-08-31 17:55 ` Andrea Parri
2018-08-29 21:10 ` [PATCH RFC LKMM 2/7] doc: Replace smp_cond_acquire() with smp_cond_load_acquire() Paul E. McKenney
2018-08-29 21:10 ` Paul E. McKenney
2018-09-14 16:59 ` Will Deacon
2018-09-14 16:59 ` Will Deacon
2018-09-14 18:20 ` Paul E. McKenney
2018-09-14 18:20 ` Paul E. McKenney
2018-08-29 21:10 ` [PATCH RFC LKMM 3/7] EXP tools/memory-model: Add more LKMM limitations Paul E. McKenney
2018-08-29 21:10 ` Paul E. McKenney
2018-08-30 9:17 ` Andrea Parri
2018-08-30 9:17 ` Andrea Parri
2018-08-30 22:18 ` Paul E. McKenney
2018-08-30 22:18 ` Paul E. McKenney
2018-08-31 9:43 ` Andrea Parri
2018-08-31 9:43 ` Andrea Parri
2018-09-06 18:34 ` Paul E. McKenney
2018-09-06 18:34 ` Paul E. McKenney
2018-08-29 21:10 ` [PATCH RFC LKMM 4/7] tools/memory-model: Fix a README typo Paul E. McKenney
2018-08-29 21:10 ` Paul E. McKenney
2018-08-29 21:10 ` [PATCH RFC LKMM 5/7] EXP tools/memory-model: Add scripts to check github litmus tests Paul E. McKenney
2018-08-29 21:10 ` Paul E. McKenney
2018-08-29 21:10 ` [PATCH RFC LKMM 6/7] EXP tools/memory-model: Make scripts take "-j" abbreviation for "--jobs" Paul E. McKenney
2018-08-29 21:10 ` Paul E. McKenney
2018-08-29 21:10 ` [PATCH RFC LKMM 7/7] EXP tools/memory-model: Add .cfg and .cat files for s390 Paul E. McKenney
2018-08-29 21:10 ` Paul E. McKenney
2018-08-31 16:06 ` Will Deacon
2018-08-31 16:06 ` Will Deacon
2018-09-01 17:08 ` Paul E. McKenney
2018-09-01 17:08 ` Paul E. McKenney
2018-09-14 16:36 ` [PATCH RFC memory-model 0/7] Memory-model changes Paul E. McKenney
2018-09-14 16:36 ` Paul E. McKenney
2018-09-14 17:19 ` Alan Stern
2018-09-14 17:19 ` Alan Stern
2018-09-14 18:29 ` Paul E. McKenney
2018-09-14 18:29 ` Paul E. McKenney
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=20180831160640.GG30626@arm.com \
--to=will.deacon@arm.com \
--cc=akiyks@gmail.com \
--cc=boqun.feng@gmail.com \
--cc=dhowells@redhat.com \
--cc=j.alglave@ucl.ac.uk \
--cc=linux-arch@vger.kernel.org \
--cc=linux-kernel@vger.kernel.org \
--cc=luc.maranget@inria.fr \
--cc=mingo@kernel.org \
--cc=npiggin@gmail.com \
--cc=parri.andrea@gmail.com \
--cc=paulmck@linux.vnet.ibm.com \
--cc=peterz@infradead.org \
--cc=stern@rowland.harvard.edu \
/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).