From: Petr Mladek <pmladek@suse.com>
To: John Ogness <john.ogness@linutronix.de>
Cc: Peter Zijlstra <peterz@infradead.org>,
linux-kernel@vger.kernel.org,
Sergey Senozhatsky <sergey.senozhatsky.work@gmail.com>,
Steven Rostedt <rostedt@goodmis.org>,
Linus Torvalds <torvalds@linux-foundation.org>,
Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
Andrea Parri <andrea.parri@amarulasolutions.com>,
Thomas Gleixner <tglx@linutronix.de>,
Sergey Senozhatsky <sergey.senozhatsky@gmail.com>
Subject: Re: [RFC PATCH v2 1/2] printk-rb: add a new printk ringbuffer implementation
Date: Thu, 27 Jun 2019 10:28:03 +0200 [thread overview]
Message-ID: <20190627082803.7aduwbwxwejyhgan@pathway.suse.cz> (raw)
In-Reply-To: <87k1d8koo3.fsf@linutronix.de>
On Wed 2019-06-26 23:43:56, John Ogness wrote:
> Here is where I have massive problems communicating. I don't understand
> why you say the barrier is _between_ newest and next. I would say the
> barrier is _on_ newest to _synchronize_ with next (or something). I am
> struggling with terminology. (To be honest, I'd much rather just post
> litmus tests.)
>
> For example, if we have:
>
> WRITE_ONCE(&a, 1);
> WRITE_ONCE(&b, 1);
> WRITE_ONCE(&c, 1);
> smp_store_release(&d, 1);
>
> and:
>
> local_d = smp_load_acquire(&d);
> local_a = READ_ONCE(&a);
> local_b = READ_ONCE(&b);
> local_c = READ_ONCE(&c);
>
> How do you describe that? Do you say the memory barrier is between a and
> d? Or between a, b, c, d? (a, b, c aren't ordered, but they are one-way
> synchronized with d).
>
> I would say there is a barrier on d to synchronize a, b, c.
Barriers are always paired. We need to know what variables are
synchonized against each other, what is the reason and where
is the counter part.
I think that it might be done many ways. I am familiar with
bariers in kernel/livepatch/ code. They use rather long description.
But I find it pretty useful especially when the problem is
complicated and more bariers are involved in a single
transition.
Best Regards,
Petr
next prev parent reply other threads:[~2019-06-27 8:28 UTC|newest]
Thread overview: 62+ messages / expand[flat|nested] mbox.gz Atom feed top
2019-06-07 16:23 [RFC PATCH v2 0/2] printk: new ringbuffer implementation John Ogness
2019-06-07 16:23 ` [RFC PATCH v2 1/2] printk-rb: add a new printk " John Ogness
2019-06-18 4:51 ` Sergey Senozhatsky
2019-06-18 22:12 ` John Ogness
2019-06-25 6:45 ` Sergey Senozhatsky
2019-06-25 7:15 ` Sergey Senozhatsky
2019-06-25 8:44 ` John Ogness
2019-06-25 9:06 ` Petr Mladek
2019-06-25 10:03 ` Sergey Senozhatsky
2019-06-25 12:03 ` John Ogness
2019-06-26 2:08 ` Sergey Senozhatsky
2019-06-26 7:16 ` John Ogness
2019-06-26 7:45 ` Sergey Senozhatsky
2019-06-26 7:47 ` Petr Mladek
2019-06-26 7:59 ` Sergey Senozhatsky
2019-06-25 9:09 ` Sergey Senozhatsky
2019-06-18 11:12 ` Peter Zijlstra
2019-06-18 22:18 ` John Ogness
2019-06-18 11:22 ` Peter Zijlstra
2019-06-18 22:30 ` John Ogness
2019-06-19 10:46 ` Andrea Parri
2019-06-20 22:50 ` John Ogness
2019-06-21 12:16 ` Andrea Parri
2019-06-19 11:08 ` Peter Zijlstra
2019-06-18 11:47 ` Peter Zijlstra
2019-06-20 22:23 ` John Ogness
2019-06-26 22:40 ` Peter Zijlstra
2019-06-26 22:53 ` Peter Zijlstra
2019-06-28 9:50 ` John Ogness
2019-06-28 15:44 ` Peter Zijlstra
2019-06-28 16:07 ` Peter Zijlstra
2019-07-01 10:39 ` John Ogness
2019-07-01 14:10 ` Peter Zijlstra
2019-07-01 14:11 ` Peter Zijlstra
2019-06-29 21:05 ` Andrea Parri
2019-06-30 2:03 ` John Ogness
2019-06-30 14:08 ` Andrea Parri
2019-07-02 14:13 ` John Ogness
2019-06-26 22:47 ` Peter Zijlstra
2019-06-21 14:05 ` Petr Mladek
2019-06-24 8:33 ` John Ogness
2019-06-24 14:09 ` Petr Mladek
2019-06-25 13:29 ` John Ogness
2019-06-26 8:29 ` Petr Mladek
2019-06-26 9:09 ` John Ogness
2019-06-26 21:16 ` Peter Zijlstra
2019-06-26 21:43 ` John Ogness
2019-06-27 8:28 ` Petr Mladek [this message]
2019-07-04 10:33 ` [PATCH POC] printk_ringbuffer: Alternative implementation of lockless printk ringbuffer Petr Mladek
2019-07-04 14:59 ` John Ogness
2019-07-08 15:23 ` Petr Mladek
2019-07-09 1:34 ` John Ogness
2019-07-09 9:06 ` Petr Mladek
2019-07-09 10:21 ` John Ogness
2019-07-09 11:58 ` Petr Mladek
2019-08-14 3:46 ` John Ogness
2019-06-24 13:55 ` [RFC PATCH v2 1/2] printk-rb: add a new printk ringbuffer implementation John Ogness
2019-06-25 8:55 ` Sergey Senozhatsky
2019-06-25 9:19 ` John Ogness
2019-06-07 16:23 ` [RFC PATCH v2 2/2] printk-rb: add test module John Ogness
2019-06-17 21:09 ` [RFC PATCH v2 0/2] printk: new ringbuffer implementation Thomas Gleixner
2019-06-18 7:15 ` Petr Mladek
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