From mboxrd@z Thu Jan  1 00:00:00 1970
Return-Path: <linux-kernel-owner@vger.kernel.org>
Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand
	id S1754761Ab1I1SVu (ORCPT <rfc822;w@1wt.eu>);
	Wed, 28 Sep 2011 14:21:50 -0400
Received: from mx2.parallels.com ([64.131.90.16]:59509 "EHLO mx2.parallels.com"
	rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP
	id S1753855Ab1I1SVt (ORCPT <rfc822;linux-kernel@vger.kernel.org>);
	Wed, 28 Sep 2011 14:21:49 -0400
Message-ID: <4E836546.7010004@parallels.com>
Date: Wed, 28 Sep 2011 15:19:50 -0300
From: Glauber Costa <glommer@parallels.com>
User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:6.0.2) Gecko/20110906 Thunderbird/6.0.2
MIME-Version: 1.0
To: Peter Zijlstra <a.p.zijlstra@chello.nl>
CC: <linux-kernel@vger.kernel.org>, <paul@paulmenage.org>,
        <lizf@cn.fujitsu.com>, <daniel.lezcano@free.fr>,
        <jbottomley@parallels.com>
Subject: Re: [RFD 1/9] Change cpustat fields to an array.
References: <1316816432-9237-1-git-send-email-glommer@parallels.com>  <1316816432-9237-2-git-send-email-glommer@parallels.com> <1317157252.21836.3.camel@twins>
In-Reply-To: <1317157252.21836.3.camel@twins>
Content-Type: text/plain; charset="UTF-8"; format=flowed
Content-Transfer-Encoding: 7bit
X-Originating-IP: [187.46.180.55]
Sender: linux-kernel-owner@vger.kernel.org
List-ID: <linux-kernel.vger.kernel.org>
X-Mailing-List: linux-kernel@vger.kernel.org

On 09/27/2011 06:00 PM, Peter Zijlstra wrote:
> On Fri, 2011-09-23 at 19:20 -0300, Glauber Costa wrote:
>>   /* Must have preemption disabled for this to be meaningful. */
>> -#define kstat_this_cpu __get_cpu_var(kstat)
>> +#define kstat_this_cpu this_cpu_ptr(task_group_kstat(current))
>
> This just lost you a debug check, the former would whinge when called
> without preemption, the new one wont. Its part of the this_cpu feature
> set to make debugging impossible.
>
>> +#else
>> +#define kstat_cpu(cpu) per_cpu(kstat, cpu)
>> +#define kstat_this_cpu (&__get_cpu_var(kstat))
>> +#endif
>>
>>   extern unsigned long long nr_context_switches(void);
>>
>> @@ -52,8 +62,8 @@ struct irq_desc;
>>   static inline void kstat_incr_irqs_this_cpu(unsigned int irq,
>>                                              struct irq_desc *desc)
>>   {
>> -       __this_cpu_inc(kstat.irqs[irq]);
>> -       __this_cpu_inc(kstat.irqs_sum);
>> +       kstat_this_cpu->irqs[irq]++;
>> +       kstat_this_cpu->irqs_sum++;
>
> It might be worth looking at the asm output of that, I think you made it
> worse, but I'm not quite sure how smart gcc is, it might just figure out
> what you meant.

I'd say leave it alone.
The biggest difference is that we don't have access to task_group(), or 
any of the fields in struct task_group. Because of that, we end up 
having to export a function to do the job of dealing with it.

Users inside sched.c won't have this problem. Outside of it, we'll add a 
call to some paths. True, mostly handle_irq paths, but I don't think 
that's what's going to kill us.

Now if we really really want to save it, we'd have to move struct 
task_group and its friends to a more visible location like a header...