linux-kernel - Re: [PATCH] tracing: separate raw syscall from syscall tracer

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Date:	Tue, 3 Nov 2009 09:23:13 +0100
From:	Frederic Weisbecker <fweisbec@...il.com>
To:	Lai Jiangshan <laijs@...fujitsu.com>
Cc:	Ingo Molnar <mingo@...e.hu>, Steven Rostedt <rostedt@...dmis.org>,
	Jason Baron <jbaron@...hat.com>,
	LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] tracing: separate raw syscall from syscall tracer

On Tue, Nov 03, 2009 at 01:45:32PM +0800, Lai Jiangshan wrote:
> 
> current syscall tracer mixes raw syscalls and real syscalls.
> 
> echo 1 > events/syscalls/enable
> And we get these from the output:
> 
> (XXXX insteads "            grep-20914 [001] 588211.446347" .. etc)
> 
> XXXX: sys_read(fd: 3, buf: 80609a8, count: 7000)
> XXXX: sys_enter: NR 3 (3, 80609a8, 7000, a, 1000, bfce8ef8)
> XXXX: sys_read -> 0x138
> XXXX: sys_exit: NR 3 = 312
> XXXX: sys_read(fd: 3, buf: 8060ae0, count: 7000)
> XXXX: sys_enter: NR 3 (3, 8060ae0, 7000, a, 1000, bfce8ef8)
> XXXX: sys_read -> 0x138
> XXXX: sys_exit: NR 3 = 312
> 
> There are 2 drawbacks here.
> A) two almost identical records are saved in ringbuffer
>    when a syscall enters or exits. (4 records for every syscall)
>    it wastes too much.
> B) the lines include "sys_enter/sys_exit" makes
>    we hardly get the useful information for the output.
> 
> The user can use this method to prevent these drawbacks:
> echo 1 > events/syscalls/enable
> echo 0 > events/syscalls/sys_enter/enable
> echo 0 > events/syscalls/sys_exit/enable
> 
> But it's not friendly for users. So we separate raw syscall
> from syscall tracer.
> 
> After this fix applied:
> syscall tracer's output (echo 1 > events/syscalls/enable):
> 
> XXXX: sys_read(fd: 3, buf: bfe87d88, count: 200)
> XXXX: sys_read -> 0x200
> XXXX: sys_fstat64(fd: 3, statbuf: bfe87c98)
> XXXX: sys_fstat64 -> 0x0
> XXXX: sys_close(fd: 3)
> 
> raw syscall tracer's output (echo 1 > events/raw_syscalls/enable):
> 
> XXXX: sys_enter: NR 175 (0, bf92bf18, bf92bf98, 8, b748cff4, bf92bef8)
> XXXX: sys_exit: NR 175 = 0
> XXXX: sys_enter: NR 175 (2, bf92bf98, 0, 8, b748cff4, bf92bef8)
> XXXX: sys_exit: NR 175 = 0
> XXXX: sys_enter: NR 3 (9, bf927f9c, 4000, b77e2518, b77dce60, bf92bff8)
> 
> Signed-off-by: Lai Jiangshan <laijs@...fujitsu.com>
> ---


Agreed, that's indeed not convenient.

Acked-by: Frederic Weisbecker <fweisbec@...il.com>

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