linux-kernel - Re: [PATCH] tracing: Cleanup the convoluted softirq tracepoints

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Date:	Tue, 19 Oct 2010 15:41:36 +0200 (CEST)
From:	Thomas Gleixner <tglx@...utronix.de>
To:	Mathieu Desnoyers <mathieu.desnoyers@...icios.com>
cc:	Koki Sanagi <sanagi.koki@...fujitsu.com>,
	Peter Zijlstra <peterz@...radead.org>,
	Ingo Molnar <mingo@...e.hu>,
	Frederic Weisbecker <fweisbec@...il.com>,
	Steven Rostedt <rostedt@...dmis.org>, nhorman@...driver.com,
	scott.a.mcmillan@...el.com, laijs@...fujitsu.com,
	"H. Peter Anvin" <hpa@...or.com>,
	LKML <linux-kernel@...r.kernel.org>, eric.dumazet@...il.com,
	kaneshige.kenji@...fujitsu.com, David Miller <davem@...emloft.net>,
	izumi.taku@...fujitsu.com, kosaki.motohiro@...fujitsu.com,
	Heiko Carstens <heiko.carstens@...ibm.com>,
	"Luck, Tony" <tony.luck@...el.com>
Subject: Re: [PATCH] tracing: Cleanup the convoluted softirq tracepoints

On Tue, 19 Oct 2010, Mathieu Desnoyers wrote:

> * Thomas Gleixner (tglx@...utronix.de) wrote:
> > With the addition of trace_softirq_raise() the softirq tracepoint got
> > even more convoluted. Why the tracepoints take two pointers to assign
> > an integer is beyond my comprehension.
> > 
> > But adding an extra case which treats the first pointer as an unsigned
> > long when the second pointer is NULL including the back and forth
> > type casting is just horrible.
> > 
> > Convert the softirq tracepoints to take a single unsigned int argument
> > for the softirq vector number and fix the call sites.
> 
> Well, there was originally a reason for this oddness. The in __do_softirq(),
> "h - softirq_ve"c computation was not needed outside of the tracepoint handler
> in the past, but it now seems to be required with the new inlined
> "kstat_incr_softirqs_this_cpu()".

Dudes, a vector computation is hardly a performance problem in that
function and definitely not an excuse for designing such horrible
interfaces.

Thanks,

	tglx
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