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Date: Sat, 20 Sep 2014 20:08:00 +0200 From: Peter Zijlstra <peterz@...radead.org> To: Steven Rostedt <rostedt@...dmis.org> Cc: Joe Perches <joe@...ches.com>, Jan Kara <jack@...e.cz>, Markus Trippelsdorf <markus@...ppelsdorf.de>, Geert Uytterhoeven <geert@...ux-m68k.org>, "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>, Andrew Morton <akpm@...ux-foundation.org> Subject: Re: [PATCH] printk: git rid of [sched_delayed] message for printk_deferred On Sat, Sep 20, 2014 at 12:30:01PM -0400, Steven Rostedt wrote: > On Sat, 20 Sep 2014 09:10:47 -0700 > Joe Perches <joe@...ches.com> wrote: > > > On Sat, 2014-09-20 at 17:47 +0200, Peter Zijlstra wrote: > > > On a whole, printk() is entirely useless for debugging these days, its > > > far too fragile/unreliable to be taken seriously so I really don't care > > > on that point either. > > > > That's unfortunate. > > > > Care to enumerate the issues that you believe make > > printk too fragile/unreliable for debugging? > > I seldom use printk these days. It's far too limited in its uses. For > one, most things worth debugging happen thousands of times a second, > and printk will just slow things down to a crawl if it is used. > Another, is that it can not be used in most critical sections (NMI > handlers and anything that deals with the scheduler). Also, as it no > longer blocks when another CPU is doing a printk, a bug can happen > which crashes the system and the output of that bug will never get > printed due to the delayed output from another CPU having the console > lock. If you're trying to debug a dying machine the early_serial_console which basically only does a stream of OUTBs to the right port is the only reliable thing. For anything else, trace_printk(). Now all I need to figure out is how to keep suspend from killing the early_serial_console setup :-) -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@...r.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
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