From: Petr Mladek <pmladek@suse.com>
To: John Ogness <john.ogness@linutronix.de>
Cc: Peter Zijlstra <peterz@infradead.org>,
Sergey Senozhatsky <sergey.senozhatsky.work@gmail.com>,
Sergey Senozhatsky <sergey.senozhatsky@gmail.com>,
Steven Rostedt <rostedt@goodmis.org>,
Linus Torvalds <torvalds@linux-foundation.org>,
Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
Andrea Parri <parri.andrea@gmail.com>,
Thomas Gleixner <tglx@linutronix.de>,
Paul McKenney <paulmck@kernel.org>,
kexec@lists.infradead.org, linux-kernel@vger.kernel.org
Subject: Re: [PATCH v4 0/4] printk: replace ringbuffer
Date: Wed, 8 Jul 2020 17:20:05 +0200 [thread overview]
Message-ID: <20200708152005.GF4751@alley> (raw)
In-Reply-To: <20200707145932.8752-1-john.ogness@linutronix.de>
On Tue 2020-07-07 17:05:28, John Ogness wrote:
> Hello,
>
> Here is a v4 for the first series to rework the printk
> subsystem. The v3 is here [0]. This first series
> only replaces the existing ringbuffer implementation. No locking
> is removed. The semantics/behavior of printk are kept the same
> except for a minor optimization that is reverted (patch 3).
>
> Despite minor changes to the ringbuffer code since v3 (comments,
> function names, very minor refactoring), the ringbuffer logic
> itself has not changed. And, in particular, the memory barriers
> have been exactly preserved from v3. For this reason I deem it
> appropriate to keep Paul's reviewed by tag (patch 2).
>
> RFC patches for various userspace tools to dump the kernel log
> are available: crash [1], makedumpfile [2], kexec-tools [3].
>
> Finally, I would like to thank some people/organizations that
> helped with performing ringbuffer stress tests on big or rare
> hardware that I do not have access to:
>
> - Prarit Bhargava of Red Hat (x86_64, ppc64le power8)
> - Michael Cree of Debian (alpha)
> - Jeff Scheel of OSU Open Source Lab (ppc64le power8 kvm)
OK, I think that we are ready to try this in linux-next.
I am going to push it there via printk/linux.git.
I have a good feeling about the patchset. The great thing is that
the access is still synchronized using logbuf_lock so that we do not
have to deal with races for the moment.
Of course, there are still many potential problems. The following comes
to my mind:
+ Bugs in the algorithm logic or implementation might prevent
showing any messages on consoles or via syslog or /dev/kmsg.
We did our best to avoid it.
+ Debugging tools accessing the buffer directly would need to
understand the new structure. Fortunately John provided
patches for the most prominent ones.
+ Small devices might complain about less effective use of memory.
Part of descriptors and dictionaries ring buffers might stay
unused. But it hopefully could get tuned.
This is basically just a start of the journey. I hope that it will be a
good one.
Best Regards,
Petr
next prev parent reply other threads:[~2020-07-08 15:20 UTC|newest]
Thread overview: 26+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-07-07 14:59 [PATCH v4 0/4] printk: replace ringbuffer John Ogness
2020-07-07 14:59 ` [PATCH v4 1/4] crash: add VMCOREINFO macro to define offset in a struct declared by typedef John Ogness
2020-07-07 14:59 ` [PATCH v4 2/4] printk: add lockless ringbuffer John Ogness
2020-07-07 14:59 ` [PATCH v4 3/4] Revert "printk: lock/unlock console only for new logbuf entries" John Ogness
2020-07-08 14:34 ` Petr Mladek
2020-07-09 1:20 ` Sergey Senozhatsky
2020-07-07 14:59 ` [PATCH v4 4/4] printk: use the lockless ringbuffer John Ogness
2020-07-07 19:25 ` kernel test robot
2020-07-08 13:18 ` John Ogness
2020-07-08 14:35 ` Petr Mladek
2020-07-08 19:24 ` kernel test robot
2020-07-09 7:14 ` [printk] 18a2dc6982: ltp.kmsg01.fail kernel test robot
2020-07-09 8:33 ` Sergey Senozhatsky
2020-07-09 10:14 ` John Ogness
2020-07-09 10:59 ` Petr Mladek
2020-07-09 11:13 ` Petr Mladek
2020-07-09 11:17 ` John Ogness
2020-07-09 12:25 ` Petr Mladek
2020-07-09 13:07 ` Sergey Senozhatsky
2020-07-09 14:41 ` Petr Mladek
2020-07-08 15:20 ` Petr Mladek [this message]
2020-07-09 7:03 ` [PATCH v4 0/4] printk: replace ringbuffer John Ogness
2020-07-10 9:11 ` Petr Mladek
2020-07-10 9:52 ` John Ogness
2020-07-10 14:15 ` Petr Mladek
2020-07-14 2:56 ` Sergey Senozhatsky
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