linux-kernel - Re: [PATCH 01/20 -v5] printk - dont wakeup klogd with interrupts disabled

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Message-Id: <1201114213.13596.29.camel@imap.mvista.com>
Date:	Wed, 23 Jan 2008 10:50:12 -0800
From:	Daniel Walker <dwalker@...sta.com>
To:	Steven Rostedt <rostedt@...dmis.org>
Cc:	LKML <linux-kernel@...r.kernel.org>, Ingo Molnar <mingo@...e.hu>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Peter Zijlstra <a.p.zijlstra@...llo.nl>,
	Christoph Hellwig <hch@...radead.org>,
	Mathieu Desnoyers <mathieu.desnoyers@...ymtl.ca>,
	Gregory Haskins <ghaskins@...ell.com>,
	Arnaldo Carvalho de Melo <acme@...stprotocols.net>,
	Thomas Gleixner <tglx@...utronix.de>,
	Tim Bird <tim.bird@...sony.com>,
	Sam Ravnborg <sam@...nborg.org>,
	"Frank Ch. Eigler" <fche@...hat.com>,
	Jan Kiszka <jan.kiszka@...mens.com>,
	John Stultz <johnstul@...ibm.com>,
	Arjan van de Ven <arjan@...radead.org>,
	Steven Rostedt <srostedt@...hat.com>
Subject: Re: [PATCH 01/20 -v5] printk - dont wakeup klogd with interrupts
	disabled


On Wed, 2008-01-23 at 13:43 -0500, Steven Rostedt wrote:
> On Wed, 23 Jan 2008, Daniel Walker wrote:
> 
> >
> > On Wed, 2008-01-23 at 13:18 -0500, Steven Rostedt wrote:
> >
> > > The wakeup hook in schedule is when we find out that we hit our max. I
> > > could postpone that somehow, but that would require more glue code than I
> > > would like to add.
> >
> > Which hook specifically ?
> 
> The wakeup tracer does a print on max when the new task is about to be
> switched to (in context_switch).

You can't move that hook to when the task actually starts running (i.e.
at the end of schedule() )..

> >
> > > As for -rt, we've disabled printk for consoles not ATOMIC safe. So the
> > > only consoles that will print in atomic sections so far are, earlyprintk
> > > and the VGA.
> >
> > Is this code you added recently for tracing?
> 
> Nope, it's been there for a few releases and had nothing to do with the
> latency tracer.
> 
> <looks at code>
> 
> Hmm, seems that only the "hack" fix is in upstream. The Red Hat version
> has the better fix, but mainline didn't get it. OK, I'll add that to the
> next -rt release.

mainline ? The problem I'm thinking of was directly tracing related..

Daniel

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