linux-kernel - Re: [PATCH 2/2] perf tools: Increase MAX_EVENT

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Message-ID: <4AB2000A.2030605@cn.fujitsu.com>
Date:	Thu, 17 Sep 2009 17:23:22 +0800
From:	Li Zefan <lizf@...fujitsu.com>
To:	Frederic Weisbecker <fweisbec@...il.com>
CC:	Peter Zijlstra <peterz@...radead.org>, Ingo Molnar <mingo@...e.hu>,
	LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 2/2] perf tools: Increase MAX_EVENT_LENGTH

>>>> The name length of some trace events is longer than 30, like
>>>> sys_enter_sched_get_priority_max and ext4_mb_discard_preallocations.
>>>>
>>>> Passing those events to perf-record will fail, try:
>>>>
>>>>   # ./perf record -f -e syscalls:sys_enter_sched_get_priority_max -F 1 -a
>>>>
>>>> Signed-off-by: Li Zefan <lizf@...fujitsu.com>
>>>> ---
>>>>  tools/perf/util/parse-events.c |    2 +-
>>>>  1 files changed, 1 insertions(+), 1 deletions(-)
>>>>
>>>> diff --git a/tools/perf/util/parse-events.c b/tools/perf/util/parse-events.c
>>>> index 034245e..c9ef944 100644
>>>> --- a/tools/perf/util/parse-events.c
>>>> +++ b/tools/perf/util/parse-events.c
>>>> @@ -145,7 +145,7 @@ static int tp_event_has_id(struct dirent *sys_dir, struct dirent *evt_dir)
>>>>  	   (strcmp(evt_dirent.d_name, "..")) &&				       \
>>>>  	   (!tp_event_has_id(&sys_dirent, &evt_dirent)))
>>>>  
>>>> -#define MAX_EVENT_LENGTH 30
>>>> +#define MAX_EVENT_LENGTH 40
>> This is userspace, is there any reason to be cheap with memory like
>> this?
>>
>> Why not stick in 1024 and be done for a while?
>>
> 
> Indeed, we may need to go even further than 40 in the future.
> But I guess 512 would be already sufficient.
> 

We are not allocating memory for all tracepoints, but only
those to be profiled, so a larger limit is OK.

But as the sys_name:evnt_name will be displayed using perf-list
cmd, I don't think the names will be too long.

Anyway, we decide to make it 512? I'll resend the patch.

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