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Message-ID: <20190904121946.GZ2369@hirez.programming.kicks-ass.net>
Date: Wed, 4 Sep 2019 14:19:46 +0200
From: Peter Zijlstra <peterz@...radead.org>
To: Petr Mladek <pmladek@...e.com>
Cc: John Ogness <john.ogness@...utronix.de>,
linux-kernel@...r.kernel.org,
Andrea Parri <andrea.parri@...rulasolutions.com>,
Sergey Senozhatsky <sergey.senozhatsky@...il.com>,
Sergey Senozhatsky <sergey.senozhatsky.work@...il.com>,
Steven Rostedt <rostedt@...dmis.org>,
Brendan Higgins <brendanhiggins@...gle.com>,
Thomas Gleixner <tglx@...utronix.de>,
Linus Torvalds <torvalds@...ux-foundation.org>,
Greg Kroah-Hartman <gregkh@...uxfoundation.org>
Subject: Re: numlist_pop(): Re: [RFC PATCH v4 1/9] printk-rb: add a new
printk ringbuffer implementation
On Tue, Aug 20, 2019 at 10:15:18AM +0200, Petr Mladek wrote:
> do {
> tail_id = atomic_long_read(&nl->tail_id);
>
> /*
> * Read might fail when the tail node has been removed
> * and reused in parallel.
> */
> if (!numlist_read(nl, tail_id, NULL, &next_id))
> continue;
>
> /* Make sure the node is not the only node on the list. */
> if (next_id == tail_id)
> return NULL;
>
> /* cC: Make sure the node is not busy. */
> if (nl->busy(tail_id, nl->busy_arg))
> return NULL;
>
> while (atomic_long_cmpxchg_relaxed(&nl->tail_id, tail_id, next_id) !=
> tail_id);
Both you and John should have a look at atomic*_try_cmpxchg*(); with
that you can write the above as:
tail_id = atomic_long_read(&nl->tai_id);
do {
...
} while (!atomic_long_try_cmpxchg_relaxed(&nl->tail_id, &tail_id, next_id));
And get better code-gen to boot.
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