linux-kernel - Re: IRQ off latency of printk is very high

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Date:	Thu, 25 Oct 2007 18:12:38 -0500
From:	Matt Mackall <mpm@...enic.com>
To:	Tim Bird <tim.bird@...sony.com>
Cc:	Mathieu Desnoyers <mathieu.desnoyers@...ymtl.ca>,
	linux kernel <linux-kernel@...r.kernel.org>,
	Ingo Molnar <mingo@...hat.com>, Jon Smirl <jonsmirl@...oo.com>
Subject: Re: IRQ off latency of printk is very high

On Thu, Oct 25, 2007 at 03:52:28PM -0700, Tim Bird wrote:
> Mathieu Desnoyers wrote:
> > It might help to read this thread I posted on LKML in January 2006
> > explaining the problem, which led to some discussion about the issue.
> > 
> > http://lkml.org/lkml/2006/6/3/48
> 
> This is very helpful.  Jon Smirl's answer seems to give the
> rationale for supporting printk output in interrupt context.
> I'm not sure, however, if extending the interrupt off period
> to cover the console output is required.  It didn't until
> Ingo changed it in 2.6.17.

Hmm, I see this at the beginning of the post-BK era (2.6.12-rc2):

	        spin_lock_irqsave(&logbuf_lock, flags);
		...
		spin_unlock(&logbuf_lock);
		call_console_drivers(_con_start, _log_end);
		local_irq_restore(flags);

-- 
Mathematics is the supreme nostalgia of our time.
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