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Date: Mon, 25 Oct 2010 15:32:37 -0700
From: "H. Peter Anvin" <hpa@zytor.com>
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To: Jason Baron <jbaron@redhat.com>
CC: Steven Rostedt <rostedt@goodmis.org>, Thomas Gleixner <tglx@linutronix.de>,
        Mathieu Desnoyers <mathieu.desnoyers@efficios.com>,
        Koki Sanagi <sanagi.koki@jp.fujitsu.com>,
        Peter Zijlstra <peterz@infradead.org>, Ingo Molnar <mingo@elte.hu>,
        Frederic Weisbecker <fweisbec@gmail.com>, nhorman@tuxdriver.com,
        scott.a.mcmillan@intel.com, laijs@cn.fujitsu.com,
        LKML <linux-kernel@vger.kernel.org>, eric.dumazet@gmail.com,
        kaneshige.kenji@jp.fujitsu.com, David Miller <davem@davemloft.net>,
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        Heiko Carstens <heiko.carstens@de.ibm.com>,
        "Luck, Tony" <tony.luck@intel.com>
Subject: Re: [PATCH] tracing: Cleanup the convoluted softirq tracepoints
References: <20101019132236.GA19197@Krystal> <alpine.LFD.2.00.1010191524160.6815@localhost6.localdomain6> <1287496495.16971.372.camel@gandalf.stny.rr.com> <alpine.LFD.2.00.1010191558250.6815@localhost6.localdomain6> <20101019142820.GA14520@Krystal> <alpine.LFD.2.00.1010191842270.6815@localhost6.localdomain6> <20101019212816.GA2855@redhat.com> <alpine.LFD.2.00.1010192347390.6815@localhost6.localdomain6> <alpine.LFD.2.00.1010200015320.6815@localhost6.localdomain6> <1287538590.16971.548.camel@gandalf.stny.rr.com> <20101020015227.GA2011@redhat.com>
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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