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

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Message-ID: <4CC60585.70503@zytor.com>
Date:	Mon, 25 Oct 2010 15:32:37 -0700
From:	"H. Peter Anvin" <hpa@...or.com>
To:	Jason Baron <jbaron@...hat.com>
CC:	Steven Rostedt <rostedt@...dmis.org>,
	Thomas Gleixner <tglx@...utronix.de>,
	Mathieu Desnoyers <mathieu.desnoyers@...icios.com>,
	Koki Sanagi <sanagi.koki@...fujitsu.com>,
	Peter Zijlstra <peterz@...radead.org>,
	Ingo Molnar <mingo@...e.hu>,
	Frederic Weisbecker <fweisbec@...il.com>,
	nhorman@...driver.com, scott.a.mcmillan@...el.com,
	laijs@...fujitsu.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 10/19/2010 06:52 PM, Jason Baron wrote:
> 
> thanks Steve. I was about to say this. When CONFIG_CC_OPTIMIZE_FOR_SIZE
> is not set we don't get the double 'jmp' and the tracepoint code is
> moved out of line. It was mentioned that a number of distros ship with
> CONFIG_CC_OPTIMIZE_FOR_SIZE not set, and as Steve mentioned my original
> patch set was conditional on !CONFIG_CC_OPTIMIZE_FOR_SIZE.
> 
> using hot/cold labels gcc can fix the CONFIG_CC_OPTIMIZE_FOR_SIZE case,
> but its a non-trivial amount of work for gcc. I was hoping that if jump
> labels are included, we could make the gcc work happen.
> 

That's fair.  I think jump labels are still a win even in the
double-jump case (especially if the the tracepoint turns into a NOP
rather than a JMP.)

Code generated with -Os has a bunch of other problems, too.

	-hpa
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