linux-kernel - Re: [PATCH 4/6] trace: trace syscall in its handler not from ptrace handler

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Date:	Thu, 29 Mar 2012 15:48:34 -0700
From:	"H. Peter Anvin" <hpa@...or.com>
To:	David Sharp <dhsharp@...gle.com>
CC:	Vaibhav Nagarnaik <vnagarnaik@...gle.com>,
	Ingo Molnar <mingo@...nel.org>,
	Steven Rostedt <rostedt@...dmis.org>,
	Frederic Weisbecker <fweisbec@...il.com>,
	Thomas Gleixner <tglx@...utronix.de>,
	Ingo Molnar <mingo@...hat.com>,
	Justin Teravest <teravest@...gle.com>,
	Laurent Chavey <chavey@...gle.com>, x86@...nel.org,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH 4/6] trace: trace syscall in its handler not from ptrace
 handler

On 03/29/2012 03:44 PM, David Sharp wrote:
>>
>> ANY increase to the fastpath is unacceptable, period.
> 
> I think the last 4 ns would probably be eliminated if we could figure
> out how to call the inline function trace_sys_enter directly instead
> of through the out-of-line wrapper we had to add to work around the
> preprocessor magic.

I already told you how to do it... override the system call table entry.
 There is a nice, juicy FUNCTION POINTER that we indirect through.

	-hpa

-- 
H. Peter Anvin, Intel Open Source Technology Center
I work for Intel.  I don't speak on their behalf.

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