linux-kernel - Re: [RFC][PATCH] tracepoints: Move the work out of line from hotpath sections

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Date:	Thu, 09 Aug 2012 16:54:02 -0700
From:	David Daney <ddaney.cavm@...il.com>
To:	"H. Peter Anvin" <hpa@...ux.intel.com>,
	Steven Rostedt <rostedt@...dmis.org>
CC:	Mathieu Desnoyers <mathieu.desnoyers@...icios.com>,
	LKML <linux-kernel@...r.kernel.org>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	Ingo Molnar <mingo@...e.hu>,
	Thomas Gleixner <tglx@...utronix.de>,
	Peter Zijlstra <peterz@...radead.org>,
	Masami Hiramatsu <masami.hiramatsu.pt@...achi.com>,
	Avi Kivity <avi@...hat.com>,
	Christoph Hellwig <hch@...radead.org>,
	Andrew Morton <akpm@...ux-foundation.org>
Subject: Re: [RFC][PATCH] tracepoints: Move the work out of line from hotpath
 sections

On 08/09/2012 04:16 PM, H. Peter Anvin wrote:
> On 08/09/2012 03:25 PM, Steven Rostedt wrote:
>>>
>>> It might be better to improve gcc to move really cold branches out of
>>> line (really, really far away), and use the compiler to do this, rather
>>> than to use an extra indirection that adds bloat and complexity to the
>>> kernel.

Oh, you mean like: -freorder-blocks-and-partition

>>
>> I think modifying gcc is something that can help more than tracing. But
>> that's been a pipe dream for such a long time that I've started dreaming
>> about winning a gold medal in the Olympics instead. Standing on the
>> podium listening to the crowd chanting your name along with your country
>> is more fun to dream about than seeing your unlikely code stop becoming
>> hurdles for the CPU sprinters.
>>
>
> At one point, maybe, but lately we have had a lot more traction from the
> gcc developers, giving us features like __fentry__ and asm goto.
>

I don't claim that -freorder-blocks-and-partition is bug free, but I 
imagine that the GCC developers would be open to fixing any bugs found.

David Daney

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