From: Jan Kara <jack@suse.cz>
To: One Thousand Gnomes <gnomes@lxorguk.ukuu.org.uk>
Cc: Jan Kara <jack@suse.cz>,
Andrew Morton <akpm@linux-foundation.org>,
LKML <linux-kernel@vger.kernel.org>,
pmladek@suse.cz, Frederic Weisbecker <fweisbec@gmail.com>,
Steven Rostedt <rostedt@goodmis.org>
Subject: Re: [PATCH 8/8] printk: Add config option for disabling printk offloading
Date: Wed, 26 Mar 2014 20:28:15 +0100 [thread overview]
Message-ID: <20140326192815.GC18118@quack.suse.cz> (raw)
In-Reply-To: <20140326172332.5f1e1bfb@alan.etchedpixels.co.uk>
On Wed 26-03-14 17:23:32, One Thousand Gnomes wrote:
> On Tue, 25 Mar 2014 18:55:01 +0100
> Jan Kara <jack@suse.cz> wrote:
>
> > Necessity for offloading of printing was observed only for large
> > systems. So add a config option (disabled by default) which removes most
> > of the overhead added by this functionality.
>
> If its an option it'll not get used. It ought to be automatic.
>
> I still think the mindset of this patch set is wrong. Only the device
> driver really knows what is good or bad. A large x86 connected to a
> network fake 16x50 serial port for example typically has a giant FIFO so
> 'bad' becomes 32K not 1000. A USB serial port already does async queueing
> so the value is 0.
I'd be very happy to take a patch which would do the propagation of
the information how fast the driver is from the driver into the printk. But
I have no knowledge of what console drivers do and how fast devices are
supposed to be and reading all that code just for the sake of this seems
like a bad investment of time to me.
I'm happy with a solution that the feature is disabled by default so people
don't have to pay the cost. For enterprise kernels which are supposed to
run on large enough machines that printk offload makes sense, the overhead
just doesn't matter IMHO.
> It also ignores priority so you might queue and loose an oops as a box
> goes down in preference to reporting debugging crap.
But that's no different to what happens now. Or am I missing something?
> All the afflicted consoles are serial, all go via the uart layer as far
> as I can see.
>
> The uart layer has a queue mechanism that could be used
I'm sorry, I don't follow here - what can the uart queueing be used for?
Honza
--
Jan Kara <jack@suse.cz>
SUSE Labs, CR
next prev parent reply other threads:[~2014-03-26 19:28 UTC|newest]
Thread overview: 30+ messages / expand[flat|nested] mbox.gz Atom feed top
2014-03-25 17:54 [PATCH 0/8 v4] printk: Cleanups and softlockup avoidance Jan Kara
2014-03-25 17:54 ` [PATCH 1/8] printk: Remove outdated comment Jan Kara
2014-03-25 17:54 ` [PATCH 2/8] printk: Release lockbuf_lock before calling console_trylock_for_printk() Jan Kara
2014-04-23 20:56 ` Andrew Morton
2014-04-24 10:18 ` Jan Kara
2014-03-25 17:54 ` [PATCH 3/8] printk: Enable interrupts " Jan Kara
2014-03-25 17:54 ` [PATCH 4/8] printk: Remove separate printk_sched buffers and use printk buf instead Jan Kara
2014-05-05 18:37 ` Steven Rostedt
2014-03-25 17:54 ` [PATCH 5/8] printk: Hand over printing to console if printing too long Jan Kara
2014-03-25 17:54 ` [PATCH 6/8] printk: Start printing handover kthreads on demand Jan Kara
2014-03-26 17:16 ` One Thousand Gnomes
2014-03-26 19:06 ` Jan Kara
2014-03-25 17:55 ` [PATCH 7/8] kernel: Avoid softlockups in stop_machine() during heavy printing Jan Kara
2014-03-25 17:55 ` [PATCH 8/8] printk: Add config option for disabling printk offloading Jan Kara
2014-03-26 17:23 ` One Thousand Gnomes
2014-03-26 19:28 ` Jan Kara [this message]
2014-04-18 18:54 ` Andrew Morton
2014-04-22 10:22 ` One Thousand Gnomes
2014-04-23 11:08 ` Jan Kara
2014-04-23 12:35 ` One Thousand Gnomes
2014-04-23 14:29 ` Jan Kara
2014-04-23 18:17 ` Andrew Morton
2014-04-23 21:16 ` One Thousand Gnomes
2014-04-23 21:41 ` Jiri Kosina
2014-04-24 14:00 ` One Thousand Gnomes
2014-05-15 21:28 ` Jan Kara
2014-04-23 9:30 ` Jan Kara
2014-04-08 14:27 ` [PATCH 0/8 v4] printk: Cleanups and softlockup avoidance Jan Kara
2014-04-08 19:02 ` Andrew Morton
-- strict thread matches above, loose matches on Subject: below --
2014-03-14 16:21 [PATCH 0/8 v3] " Jan Kara
2014-03-14 16:21 ` [PATCH 8/8] printk: Add config option for disabling printk offloading Jan Kara
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