linux-kernel - Re: [PATCH v4 1/5] irq: add tracepoint to softirq

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Date:	Fri, 03 Sep 2010 11:39:36 -0400
From:	Steven Rostedt <rostedt@...dmis.org>
To:	Frederic Weisbecker <fweisbec@...il.com>
Cc:	Koki Sanagi <sanagi.koki@...fujitsu.com>, netdev@...r.kernel.org,
	linux-kernel@...r.kernel.org, davem@...emloft.net,
	kaneshige.kenji@...fujitsu.com, izumi.taku@...fujitsu.com,
	kosaki.motohiro@...fujitsu.com, nhorman@...driver.com,
	laijs@...fujitsu.com, scott.a.mcmillan@...el.com,
	eric.dumazet@...il.com, mathieu.desnoyers@...ymtl.ca
Subject: Re: [PATCH v4 1/5] irq: add tracepoint to softirq_raise

On Fri, 2010-09-03 at 17:29 +0200, Frederic Weisbecker wrote:

> >  #define softirq_name(sirq) { sirq##_SOFTIRQ, #sirq }
> >  #define show_softirq_name(val)				\
> > @@ -93,7 +95,10 @@ DECLARE_EVENT_CLASS(softirq,
> >  	),
> >  
> >  	TP_fast_assign(
> > -		__entry->vec = (int)(h - vec);
> > +		if (vec)
> > +			__entry->vec = (int)(h - vec);
> > +		else
> > +			__entry->vec = *((int *)h);
> >  	),
> 
> 
> 
> It seems that this will break softirq_entry/exit tracepoints.
> __entry->vec will deref vec->action() for these two, which is not
> what we want.

But for trace_softirq_entry and trace_softirq_exit, vec will not be
NULL.


> 
> If you can't have the same tracepoint signature for the three, just
> split the new one in a seperate TRACE_EVENT().

It may be a bit of a hack, and questionable about adding another
TRACE_EVENT(). There still is a pretty good space savings in using
DEFINE_EVENT() over TRACE_EVENT() though.

-- Steve



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