linux-kernel - Re: [RFC][PATCH 3/2] x86/jump labels: Count and display the short jumps used

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Date:	Wed, 07 Aug 2013 16:33:26 -0400
From:	Steven Rostedt <rostedt@...dmis.org>
To:	Jason Baron <jbaron@...mai.com>
Cc:	Linus Torvalds <torvalds@...ux-foundation.org>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	"H. Peter Anvin" <hpa@...or.com>, Ingo Molnar <mingo@...nel.org>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Thomas Gleixner <tglx@...utronix.de>,
	Peter Zijlstra <peterz@...radead.org>
Subject: Re: [RFC][PATCH 3/2] x86/jump labels: Count and display the short
 jumps used

On Wed, 2013-08-07 at 16:19 -0400, Jason Baron wrote:

> The whole point of the thread started with wanting to move the default
> 'disabled' branch further out-of-line. We could get there with better
> compiler support for the 'cold' label attribute. Thus, in theory the
> whole 2-byte jmp is just an intermediate step. (Yeah, I know that
> support doesn't seem to be happening anytime soon...)
> 

Actually, Ideally, we would move the bulk of the tracing code out of
line, but we can have the jump to the tracing code still in line, and
the nop jump to it.


	[ hot path]
	jmp trace / nop
1:

	[...]


trace:
	jmp trace_main_code
	jmp 1b


Then that jmp trace can still be a 2 byte op.

-- Steve


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