linux-kernel - Re: [PATCH] tracer for sys_open()

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Date:	Wed, 28 Jan 2009 14:05:20 -0800
From:	"Kok, Auke" <auke-jan.h.kok@...el.com>
To:	Frederic Weisbecker <fweisbec@...il.com>
CC:	Arnaldo Carvalho de Melo <acme@...hat.com>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	powertop ml <power@...host.org>,
	Arjan van de Ven <arjan@...ux.intel.com>,
	Ingo Molnar <mingo@...e.hu>,
	"srostedt@...hat.com" <srostedt@...hat.com>,
	"Frank Ch. Eigler" <fche@...hat.com>,
	Neil Horman <nhorman@...driver.com>,
	"Kok, Auke" <auke@...-projects.org>
Subject: Re: [PATCH] tracer for sys_open() - sreadahead

Frederic Weisbecker wrote:
> On Tue, Jan 27, 2009 at 06:51:37PM -0200, Arnaldo Carvalho de Melo wrote:
>> Em Tue, Jan 27, 2009 at 12:08:04PM -0800, Kok, Auke escreveu:
>>> This tracer monitors regular file open() syscalls. This is a fast
>>> and low-overhead alternative to strace, and does not allow or
>>> require to be attached to every process.
>>>
>>> The tracer only logs succesfull calls, as those are the only ones we
>>> are currently interested in, and we can determine the absolute path
>>> of these files as we log.
>>>
>>> Signed-off-by: Auke Kok <auke-jan.h.kok@...el.com>
>> <SNIP>
>>  
>>> diff --git a/kernel/trace/trace.h b/kernel/trace/trace.h
>>> index 4d3d381..24c17d2 100644
>>> --- a/kernel/trace/trace.h
>>> +++ b/kernel/trace/trace.h
>>> @@ -30,6 +30,7 @@ enum trace_type {
>>>         TRACE_USER_STACK,
>>>         TRACE_HW_BRANCHES,
>>>         TRACE_POWER,
>>> +       TRACE_OPEN,
>> Why not a TRACE_VFS or TRACE_SYSCALL and then multiplex there open,
>> close, etc? trace_assign_type will get humongous in no time this way.
> 
> 
> That's what I was about to answer too.
> That would be sad to find one tracer for open, one for read, one for write...
> 
>  
>> TRACE_BLK does multiplexing, as does TRACE_PROCESS that Frank just
>> posted too, and I'm working on a plugin for the patch that Neil
>> submitted for the socket layer that also will need an entry there for
>> its tracepoints.
>>
>> Frederic, it seems that discussion about subtypes has to continue :-)
> 
> 
> Indeed, that becomes serious :-)
> 

I totally agree - this tracer was purely made quick-and-dirty to get sreadahead to
the next level. The in-kernel syscall trace facility is extremely potent and I
don't doubt that my patch may have been found slightly absurd by some :)

In all it was not productive to write a giant trace facility just to get
sreadahead one tracer type. Now that the code works and the benefit is proven, I'm
happy to see if we can work on making a decent long-term non-specialistic solution.

Auke

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