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Subject: Re: [RFC][PATCH 7/7] perf: Optimize sw events
From: Peter Zijlstra <peterz@infradead.org>
To: Ingo Molnar <mingo@elte.hu>
Cc: Frederic Weisbecker <fweisbec@gmail.com>, Jason Baron <jbaron@redhat.com>,
        linux-kernel@vger.kernel.org, David Miller <davem@davemloft.net>,
        Mike Galbraith <efault@gmx.de>, Steven Rostedt <rostedt@goodmis.org>,
        "H. Peter Anvin" <hpa@zytor.com>
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Date: Fri, 15 Oct 2010 16:57:07 +0200
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On Fri, 2010-10-15 at 11:16 +0200, Peter Zijlstra wrote:
> On Thu, 2010-10-14 at 22:34 +0200, Peter Zijlstra wrote:
> 
> > Index: linux-2.6/include/linux/perf_event.h
> > ===================================================================
> > --- linux-2.6.orig/include/linux/perf_event.h
> > +++ linux-2.6/include/linux/perf_event.h
> > @@ -1013,15 +1013,17 @@ static inline void perf_fetch_caller_reg
> >  static inline void
> >  perf_sw_event(u32 event_id, u64 nr, int nmi, struct pt_regs *regs, u64 addr)
> >  {
> > -	if (atomic_read(&perf_swevent_enabled[event_id])) {
> > -		struct pt_regs hot_regs;
> > +	struct pt_regs hot_regs;
> >  
> > -		if (!regs) {
> > -			perf_fetch_caller_regs(&hot_regs);
> > -			regs = &hot_regs;
> > -		}
> > -		__perf_sw_event(event_id, nr, nmi, regs, addr);
> > +	JUMP_LABEL(&perf_swevent_enabled[event_id], have_event);
> > +	return;
> > +
> > +have_event:
> > +	if (!regs) {
> > +		perf_fetch_caller_regs(&hot_regs);
> > +		regs = &hot_regs;
> >  	}
> > +	__perf_sw_event(event_id, nr, nmi, regs, addr);
> >  }
> >  
> 
> OK, so it appears I only compile tested this bit without jump_label
> support, with that bit added back this horribly fails to compile like:
> 
> In file included from /usr/src/linux-2.6/arch/x86/mm/fault.c:13:
> /usr/src/linux-2.6/include/linux/perf_event.h: In function ‘perf_sw_event.clone.0’:
> /usr/src/linux-2.6/include/linux/perf_event.h:1018: warning: asm operand 0 probably doesn’t match constraints
> /usr/src/linux-2.6/include/linux/perf_event.h:1018: error: impossible constraint in ‘asm’
> 

Ah, figured it out, it needs __attribute__((always_inline)), otherwise
we end up with multiple keys for one label, which will clealy not work.

I thought we had a __force_inline macro but I can't seem to find that.