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

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Message-ID: <4F74B42F.3050100@zytor.com>
Date:	Thu, 29 Mar 2012 12:12:47 -0700
From:	"H. Peter Anvin" <hpa@...or.com>
To:	Vaibhav Nagarnaik <vnagarnaik@...gle.com>
CC:	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>,
	David Sharp <dhsharp@...gle.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 12:02 PM, Vaibhav Nagarnaik wrote:
> 
> Thanks for the feedback. I had missed this added latency due to this
> patch when tracing is disabled.
> 
> To fix that, instead of a TIF flag, I am using a flag in the
> current->trace bitmap. I check that flag before jumping to the tracing
> function. That reduces the latency from 83 ns/call to 74 ns/call.
> 

ANY increase to the fastpath is unacceptable, period.

Furthermore, as I have discussed with some people over the last few
days, I think we should consider the whole syscall tracing interface set
to be a mistake and deprecate it.  There are much better ways to
accomplish something that will work more reliable without all these thunks.

	-hpa

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

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