linux-kernel - Re: [PATCH] percpu: use KERN_CONT in pcpu_dump_alloc

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Date:	Sun, 1 Apr 2012 15:29:51 +0200
From:	Kay Sievers <kay@...y.org>
To:	Tejun Heo <tj@...nel.org>
Cc:	Joe Perches <joe@...ches.com>,
	Christoph Lameter <cl@...ux-foundation.org>,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH] percpu: use KERN_CONT in pcpu_dump_alloc_info()

On Thu, Mar 29, 2012 at 22:11, Tejun Heo <tj@...nel.org> wrote:
> On Thu, Mar 29, 2012 at 1:06 PM, Joe Perches <joe@...ches.com> wrote:
>> It'd be just for avoidance of any other possible
>> interleaving from other threads.
>>
>> It's an __init function so that's not too likely,
>> but if it every happens...
>
> Ah, okay.  Forgot about that.  Yeah, the kernel is single threaded at
> that point, so it shouldn't matter. The code is rather complex so
> something simpler would be nice, I agree.
>
> Another thing is that we seem to have structured logging coming our
> way and maybe userspace can deal with racing continuing printks? Not
> sure how different streams could be distinguished tho. Maybe the
> printing task can be used to group them? Kay, is this something
> structured logging would solve?

The kernel's printk() uses a static scratch buffer of 1024 chars. The
prototype for the printk() with facility and structure support I have,
does a bit better and more reliable 'buffered IO' than the current
one.

If interleaved printk messages are still a problem, we could allocate
a per-cpu scratch buffer and all continuation lines which stay on the
same CPU would share the same buffer before it is committed to the
global log buffer.

Kay
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