linux-arch.vger.kernel.org archive mirror
 help / color / mirror / Atom feed
From: Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
To: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Marco Elver <elver@google.com>, Will Deacon <will@kernel.org>,
	paulmck <paulmck@kernel.org>,
	Peter Zijlstra <peterz@infradead.org>,
	Segher Boessenkool <segher@kernel.crashing.org>,
	linux-kernel <linux-kernel@vger.kernel.org>,
	Alan Stern <stern@rowland.harvard.edu>,
	Andrea Parri <parri.andrea@gmail.com>,
	Boqun Feng <boqun.feng@gmail.com>,
	Nicholas Piggin <npiggin@gmail.com>,
	David Howells <dhowells@redhat.com>,
	j alglave <j.alglave@ucl.ac.uk>,
	luc maranget <luc.maranget@inria.fr>, akiyks <akiyks@gmail.com>,
	linux-toolchains <linux-toolchains@vger.kernel.org>,
	linux-arch <linux-arch@vger.kernel.org>
Subject: Re: [RFC PATCH] LKMM: Add ctrl_dep() macro for control dependency
Date: Fri, 1 Oct 2021 13:28:01 -0400 (EDT)	[thread overview]
Message-ID: <1097444747.48074.1633109281556.JavaMail.zimbra@efficios.com> (raw)
In-Reply-To: <CAHk-=whcN4ACLFvst0THwwpUFK4DDSM4O_frSoUQJ1m+0ENWjw@mail.gmail.com>

----- On Oct 1, 2021, at 12:20 PM, Linus Torvalds torvalds@linux-foundation.org wrote:
[...]
> But again - a lot of these made-up examples are exactly that: made up.
> For us to have a ctrl_dep() macro, I really want to see an actual
> honest-to-goodness case of this that we can point to.

I've spent some quality time staring at generated assembler diff in the past
days, and looking for code patterns of refcount_dec_and_test users, without
much success. There are some cases which end up working by chance, e.g. in
cases where the if leg has a smp_acquire__after_ctrl_dep and the else leg has
code that emits a barrier(), but I did not find any buggy generated
code per se. In order to observe those issues in real life, we would
really need to have identical then/else legs to the branch.

Thanks,

Mathieu

-- 
Mathieu Desnoyers
EfficiOS Inc.
http://www.efficios.com

  reply	other threads:[~2021-10-01 17:28 UTC|newest]

Thread overview: 35+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2021-09-28 21:15 [RFC PATCH] LKMM: Add ctrl_dep() macro for control dependency Mathieu Desnoyers
2021-09-29 12:06 ` Marco Elver
2021-10-01 15:45   ` Mathieu Desnoyers
2021-10-01 16:20     ` Linus Torvalds
2021-10-01 17:28       ` Mathieu Desnoyers [this message]
2021-10-01 18:18         ` Linus Torvalds
2021-09-29 12:28 ` Florian Weimer
2021-09-29 17:41   ` Segher Boessenkool
2021-09-29 19:46     ` Florian Weimer
2021-10-01 16:13     ` Mathieu Desnoyers
2021-10-01 16:26       ` Florian Weimer
2021-10-01 16:35         ` Linus Torvalds
2021-10-10 14:02           ` Florian Weimer
2021-10-14  0:01             ` Paul E. McKenney
2021-10-14  2:14               ` Alan Stern
2021-10-14 16:14                 ` Paul E. McKenney
2021-10-14 15:58               ` Florian Weimer
2021-10-14 16:23                 ` Paul E. McKenney
2021-10-14 18:19                   ` Florian Weimer
2021-10-14 21:09                     ` Paul E. McKenney
2021-10-14 22:36                       ` Linus Torvalds
2021-09-30 13:28   ` Mathieu Desnoyers
2021-09-29 14:47 ` Linus Torvalds
2021-09-29 14:54   ` Linus Torvalds
2021-09-29 19:50     ` Mathieu Desnoyers
2021-09-29 20:13       ` Mathieu Desnoyers
2021-09-29 19:27   ` Mathieu Desnoyers
2021-09-29 22:14     ` Linus Torvalds
2021-09-29 21:47 ` Segher Boessenkool
2021-09-29 23:57   ` Paul E. McKenney
2021-10-01 15:28     ` Mathieu Desnoyers
2021-10-01 22:53       ` Paul E. McKenney
2021-10-01 19:10     ` Segher Boessenkool
2021-10-01 22:50       ` Paul E. McKenney
2021-10-02 14:29       ` Alan Stern

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=1097444747.48074.1633109281556.JavaMail.zimbra@efficios.com \
    --to=mathieu.desnoyers@efficios.com \
    --cc=akiyks@gmail.com \
    --cc=boqun.feng@gmail.com \
    --cc=dhowells@redhat.com \
    --cc=elver@google.com \
    --cc=j.alglave@ucl.ac.uk \
    --cc=linux-arch@vger.kernel.org \
    --cc=linux-kernel@vger.kernel.org \
    --cc=linux-toolchains@vger.kernel.org \
    --cc=luc.maranget@inria.fr \
    --cc=npiggin@gmail.com \
    --cc=parri.andrea@gmail.com \
    --cc=paulmck@kernel.org \
    --cc=peterz@infradead.org \
    --cc=segher@kernel.crashing.org \
    --cc=stern@rowland.harvard.edu \
    --cc=torvalds@linux-foundation.org \
    --cc=will@kernel.org \
    /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).