linux-kernel - Re: -rt doesn't compile for UML

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Message-ID: <20071128160501.GA7986@elte.hu>
Date:	Wed, 28 Nov 2007 17:05:01 +0100
From:	Ingo Molnar <mingo@...e.hu>
To:	Miklos Szeredi <miklos@...redi.hu>
Cc:	jdike@...toit.com, user-mode-linux-devel@...ts.sourceforge.net,
	linux-kernel@...r.kernel.org
Subject: Re: -rt doesn't compile for UML


* Miklos Szeredi <miklos@...redi.hu> wrote:

> > it doesnt need it - turn IRQOFF_TRACING off.
> 
> # CONFIG_CRITICAL_IRQSOFF_TIMING is not set
> 
> This seems to be off.
> 
> But latency_trace.c uses irqs_disabled_flags(), which is defined in 
> <linux/irqflags.h> only if CONFIG_TRACE_IRQFLAGS_SUPPORT is set.
> 
> So perhaps latency_trace.c should be using raw_irqs_disabled_flags() 
> instead.  But UML doesn't define that either and I have no idea how to 
> do that, so this is still not solved yet.

irqs_disabled_flags() gives us a nonessential bit of the trace output:

                 _------=> CPU#
                / _-----=> irqs-off
               | / _----=> need-resched
               || / _---=> hardirq/softirq
               ||| / _--=> preempt-depth
               |||| /
               |||||     delay
   cmd     pid ||||| time  |   caller
      \   /    |||||   \   |   /
 privoxy-12926 1.Ns1    0us : ktime_get_ts (ktime_get)
 privoxy-12926 1.Ns1    0us : getnstimeofday (ktime_get_ts)
 privoxy-12926 1.Ns1    1us : set_normalized_timespec (ktime_get_ts)
 privoxy-12926 1.Ns1    1us : rb_first (htb_dequeue)

it's the 'irqs-off' flag, which is 'd', 'D' or '.'.

so you can define irqs_off_flags to always-0 and you should be able to 
get pretty good traces still. It should have no functional impact.

	Ingo
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