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Message-ID: <56D0440E.1000605@gmail.com>
Date: Fri, 26 Feb 2016 21:24:46 +0900
From: Taeung Song <treeze.taeung@...il.com>
To: Arnaldo Carvalho de Melo <arnaldo.melo@...il.com>
Cc: Steven Rostedt <rostedt@...dmis.org>,
Ingo Molnar <mingo@...hat.com>, Jiri Olsa <jolsa@...nel.org>,
Namhyung Kim <namhyung@...nel.org>,
linux-kernel@...r.kernel.org, Thomas Gleixner <tglx@...utronix.de>,
Lai Jiangshan <jiangshanlai@...il.com>
Subject: Re: [PATCH v2 1/3] tracing/syscalls: Rename variable 'nr' to
'syscall_nr'
Hi, Arnaldo
On 02/26/2016 03:42 AM, Arnaldo Carvalho de Melo wrote:
> Em Fri, Feb 26, 2016 at 03:31:19AM +0900, Taeung Song escreveu:
>> Hi, Arnaldo
>>
>> On 02/26/2016 02:57 AM, Arnaldo Carvalho de Melo wrote:
>>> Em Fri, Feb 26, 2016 at 02:38:57AM +0900, Taeung Song escreveu:
>>>> There is a problem about duplicated variable name i.e.
>>>> # cat /sys/kernel/debug/tracing/events/syscalls/sys_enter_io_getevents/format
>>>> name: sys_enter_io_getevents
>>>> ID: 739
>>>> format:
>>>> field:unsigned short common_type; offset:0; size:2; signed:0;
>>>> field:unsigned char common_flags; offset:2; size:1; signed:0;
>>>> field:unsigned char common_preempt_count; offset:3; size:1; signed:0;
>>>> field:int common_pid;offset:4;size:4;signed:1;
>>>> field:int nr; offset:8; size:4; signed:1;
>>>> field:aio_context_t ctx_id; offset:16; size:8; signed:0;
>>>> field:long min_nr; offset:24; size:8; signed:0;
>>>> field:long nr; offset:32; size:8; signed:0;
>>>> field:struct io_event * events; offset:40; size:8; signed:0;
>>>> field:struct timespec * timeout; offset:48; size:8; signed:0;
>>>>
>>>> print fmt: "ctx_id: 0x%08lx, min_nr: 0x%08lx, nr: 0x%08lx,
>>>> events: 0x%08lx, timeout: 0x%08lx", ((unsigned long)(REC->ctx_id)),
>>>> ((unsigned long)(REC->min_nr)), ((unsigned long)(REC->nr)),
>>>> ((unsigned long)(REC->events)), ((unsigned long)(REC->timeout))
>>>>
>>>> As above 'int nr;' and 'long nr;' variables have
>>>> duplicated name so problems are occurred in perf-script i.e.
>>>>
>>>> # perf record -e syscalls:*
>>>> # perf script -g python
>>>> # perf script -s perf-script.py
>>>> File "perf-script.py", line 8694
>>>> def syscalls__sys_enter_io_getevents(event_name, context, common_cpu,
>>>> SyntaxError: duplicate argument 'nr' in function definition
>>>> Error running python script perf-script.py
>>>
>>> Please test this with 'perf trace', which this patch breaks, this patch
>>> should make it understand this 3rd variation of the non common list of
>>> fields in syscall tracepoints:
>>
>> OK, I will test it.
>> But IMHO, I think the bottom change has a problem.
>> Because sys_enter_io_getevent() has a argument 'long nr'.
>
> It doesn't matter
>
>> So this if statement must not have strcmp(sc->args->name, "nr") == 0.
>
> This is checking for the first variable, if that has that name, it
> should be discarded, as in the past it wasn't there, so for the tool to
> work on kernels with "nr" as the first (for the syscall number) variable
> and for kernels without it, we must check and discard.
>
> Now we must check and discard the first "nr" (for kernels with this
> meaning the syscall number) and also if it is called "syscall_nr").
> The other fields are taken as the syscall arguments, in the order that
> they come, that is what what we will match with what is in the
> raw_syscalls:sys_enter args array:
>
> [root@...et ~]# cat
> /sys/kernel/debug/tracing/events/raw_syscalls/sys_enter/format
> name: sys_enter
> ID: 17
> format:
> field:unsigned short common_type; offset:0; size:2; signed:0;
> field:unsigned char common_flags; offset:2; size:1; signed:0;
> field:unsigned char common_preempt_count; offset:3; size:1; signed:0;
> field:int common_pid; offset:4; size:4; signed:1;
>
> field:long id; offset:8; size:8; signed:1;
> field:unsigned long args[6]; offset:16; size:48; signed:0;
>
> print fmt: "NR %ld (%lx, %lx, %lx, %lx, %lx, %lx)", REC->id,
> REC->args[0], REC->args[1], REC->args[2], REC->args[3], REC->args[4],
> REC->args[5]
> [root@...et ~]#
>
>> + if (sc->args && strcmp(sc->args->name, "syscall_nr") == 0) {
>>
>> I think the above instance seem better than the bottom.
>>
>> + if (sc->args && (strcmp(sc->args->name, "syscall_nr") ||
>> strcmp(sc->args->name, "nr")) == 0) {
>
> Right in this 'if' body we do:
>
> sc->args = sc->args->next;
> sc->nr_args--;
>
> something like that.
>
> - Arnaldo
>
>> But I'll test again with perf-trace.
>
> Right, look at the output of 'perf trace' before and after, so that you
> can check if, say, we're using that syscall_nr value as the fd for the
> 'write' syscall ('fd' comes right after 'nr'/'syscall_nr').
>
Sorry, I'm late.
I tested perf-trace with the bottom change.
(does not rename it to '__syscall_nr' on kernel)
+ if (sc->args && (strcmp(sc->args->name, "__syscall_nr") ||
strcmp(sc->args->name, "nr")) == 0) {
sc->args = sc->args->next;
--sc->nr_args;
}
But there are some problems as below.
0.322 ( 0.012 ms): a.out/27045 write(nr: 3, fd: 4196046, buf: 0x4,
count: 2140 ) = 4
So, I modified the above change. (I'll send it as new patch)
And then I tested again as below
0.345 ( 0.016 ms): a.out/27695 write(fd: 3, buf: 0x4006ce, count: 4 ) = 4
And I tested perf-trace with renamed '__syscall_nr' on modified kernel.
Everything is ok for aught I know.
0.345 ( 0.016 ms): a.out/27695 write(fd: 3, buf: 0x4006ce, count: 4 ) = 4
I'm writing another patchset. I'll send it soon.
Thanks,
Taeung
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