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Date: Wed, 20 Oct 2010 00:27:25 +0200
Subject: Re: [PATCH] tracing: Cleanup the convoluted softirq tracepoints
From: "Peter Zijlstra" <a.p.zijlstra@chello.nl>
To: "Steven Rostedt" <rostedt@goodmis.org>
Cc: "H. Peter Anvin" <hpa@zytor.com>, "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>,
        izumi.taku@jp.fujitsu.com, kosaki.motohiro@jp.fujitsu.com,
        "Heiko Carstens" <heiko.carstens@de.ibm.com>,
        "Luck, Tony" <tony.luck@intel.com>
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On Wed, October 20, 2010 12:23 am, Steven Rostedt wrote:

>> static __always_inline __pure bool __switch_point(...)
>> {
>> 	asm goto("1: " JUMP_LABEL_INITIAL_NOP
>> 		 /* ... patching stuff */
>> 		: : : : t_jump);
>> 	return false;
>> t_jump:
>> 	return true;
>> }
>>
>> #define SWITCH_POINT(x) unlikely(__switch_point(x))
>>
>> I *suspect* this will resolve the need for hot/cold labels just fine.
>
> Interesting, we could try this.

Due to not actually having a sane key type the above is not easy to
implement, but I tried:

#define _SWITCH_POINT(x)\
({                                                              \
        __label__ jl_enabled;                                   \
        bool ret = true;                                        \
        JUMP_LABEL(x, jl_enabled);                              \
        ret = false;                                            \
jl_enabled:                                                     \
        ret;            })

#define SWITCH_POINT(x) unlikely(_SWITCH_POINT(x))

#define COND_STMT(key, stmt)                                    \
do {                                                            \
        if (SWITCH_POINT(key)) {                                \
                stmt;                                           \
        }                                                       \
} while (0)


and that's still generating these double jumps.