linux-kernel - Re: [PATCH 2/2] perf_counter: optimize for perf_event_init

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Date:	Fri, 25 Sep 2009 09:23:42 +0800
From:	Xiao Guangrong <xiaoguangrong@...fujitsu.com>
To:	Peter Zijlstra <peterz@...radead.org>
CC:	Ingo Molnar <mingo@...e.hu>, Paul Mackerras <paulus@...ba.org>,
	LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 2/2] perf_counter: optimize for perf_event_init_task()



Peter Zijlstra wrote:
> On Wed, 2009-09-23 at 16:13 +0800, Xiao Guangrong wrote:
>> We can traverse ctx->group_list to get all group leader, it should be safe
>> since we hold ctx->mutex
> 
> I don't think we need that WARN_ON_ONCE there.
> 

I'll remove it

Thanks,
Xiao

>> Signed-off-by: Xiao Guangrong <xiaoguangrong@...fujitsu.com>
>> ---
>>  kernel/perf_event.c |    5 ++---
>>  1 files changed, 2 insertions(+), 3 deletions(-)
>>
>> diff --git a/kernel/perf_event.c b/kernel/perf_event.c
>> index 9ca975a..4e6e822 100644
>> --- a/kernel/perf_event.c
>> +++ b/kernel/perf_event.c
>> @@ -4786,9 +4786,8 @@ int perf_event_init_task(struct task_struct *child)
>>  	 * We dont have to disable NMIs - we are only looking at
>>  	 * the list, not manipulating it:
>>  	 */
>> -	list_for_each_entry_rcu(event, &parent_ctx->event_list, event_entry) {
>> -		if (event != event->group_leader)
>> -			continue;
>> +	list_for_each_entry(event, &parent_ctx->group_list, group_entry) {
>> +		WARN_ON_ONCE(event != event->group_leader);
>>  
>>  		if (!event->attr.inherit) {
>>  			inherited_all = 0;
> 
> 
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