linux-kernel - Re: [PATCH 2/2] tracing: syscall_regfunc() should not skip kernel threads

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Date:	Tue, 19 Mar 2013 14:27:38 -0700
From:	"H. Peter Anvin" <hpa@...ux.intel.com>
To:	Steven Rostedt <rostedt@...dmis.org>
CC:	David Howells <dhowells@...hat.com>,
	Oleg Nesterov <oleg@...hat.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Ingo Molnar <mingo@...e.hu>,
	Frederic Weisbecker <fweisbec@...il.com>,
	linux-kernel@...r.kernel.org,
	linux-arch <linux-arch@...r.kernel.org>
Subject: Re: [PATCH 2/2] tracing: syscall_regfunc() should not skip kernel
 threads

On 03/19/2013 08:36 AM, Steven Rostedt wrote:
> On Tue, 2013-03-19 at 15:10 +0000, David Howells wrote:
>> Steven Rostedt <rostedt@...dmis.org> wrote:
>>
>>> Why? If we remove the tracepoint from the slowpath and use a table swap,
>>> then we wouldn't need to use the slowpath at all.
>>
>> How are you engineering a table swap?  Do you patch the system call code to
>> change the immediate address loaded or do you put in a level of indirection?
> 
> Patching the call site would probably be the easiest method.
> 
> We've gotten pretty good at doing that ;-)
> 

Yes, given that the machinery is already there we might as well use it.

	-hpa


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