linux-kernel - Re: [PATCH 1/5] ftrace: Synchronize variable setting with breakpoints

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Date:	Thu, 31 May 2012 16:40:33 -0400
From:	Steven Rostedt <rostedt@...dmis.org>
To:	Peter Zijlstra <peterz@...radead.org>
Cc:	Mathieu Desnoyers <mathieu.desnoyers@...icios.com>,
	linux-kernel@...r.kernel.org, Ingo Molnar <mingo@...e.hu>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Frederic Weisbecker <fweisbec@...il.com>,
	Masami Hiramatsu <masami.hiramatsu.pt@...achi.com>,
	"H. Peter Anvin" <hpa@...or.com>, Dave Jones <davej@...hat.com>,
	Andi Kleen <ak@...ux.intel.com>, acme <acme@...stprotocols.net>
Subject: Re: [PATCH 1/5] ftrace: Synchronize variable setting with
 breakpoints

On Thu, 2012-05-31 at 16:37 -0400, Steven Rostedt wrote:
> On Thu, 2012-05-31 at 22:26 +0200, Peter Zijlstra wrote:
> 
> > Right, but when you loose stop-machine you could simply do 30k
> > kmap_atomic/kunmap_atomic's consecutively since you're not holding
> > anybody up.
> 
> It requires 3 IPIs per update too. Thus that's 90,000 IPIs you are
> blasting^Wsending to all CPUs.
> 

Note, currently ftrace adds breakpoints to all locations, sends out the
IPIs, modifies the code, sends out the IPIs and then removes the
breakpoint, sends out the IPIs. 

Just three IPIs for those 30,000 updates.

-- Steve


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