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 S1754552Ab0CSBbW (ORCPT <rfc822;w@1wt.eu>);
	Thu, 18 Mar 2010 21:31:22 -0400
Received: from mail-bw0-f209.google.com ([209.85.218.209]:40891 "EHLO
	mail-bw0-f209.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org
	with ESMTP id S1752618Ab0CSBbR (ORCPT
	<rfc822;linux-kernel@vger.kernel.org>);
	Thu, 18 Mar 2010 21:31:17 -0400
DomainKey-Signature: a=rsa-sha1; c=nofws;
        d=gmail.com; s=gamma;
        h=date:from:to:cc:subject:message-id:references:mime-version
         :content-type:content-disposition:in-reply-to:user-agent;
        b=Q94spLpj0TmtkGpNHLSK8bTDN6t6IE8XkcgGvTHafDjOmijpUTHYohvfWbzKsfYxW5
         Ux70X4xvEVdBzWQ0igsg47ZALa4WlefG9Fc7VGCBYsBsgPBhvUPQFqXTOVhwiGC5F9Hb
         ERmuSrc5XZtFOAWC7aLbTXOiNCA1I+v4cZZWk=
Date: Fri, 19 Mar 2010 02:31:22 +0100
From: Frederic Weisbecker <fweisbec@gmail.com>
To: David Miller <davem@davemloft.net>
Cc: tj@kernel.org, sparclinux@vger.kernel.org, linux-kernel@vger.kernel.org
Subject: Re: [BUG] percpu misaligned allocation
Message-ID: <20100319013119.GB22095@nowhere>
References: <20100318044930.GC5045@nowhere> <4BA1F2BA.30604@kernel.org> <20100318.175413.183069013.davem@davemloft.net>
MIME-Version: 1.0
Content-Type: text/plain; charset=us-ascii
Content-Disposition: inline
In-Reply-To: <20100318.175413.183069013.davem@davemloft.net>
User-Agent: Mutt/1.5.18 (2008-05-17)
Sender: linux-kernel-owner@vger.kernel.org
List-ID: <linux-kernel.vger.kernel.org>
X-Mailing-List: linux-kernel@vger.kernel.org

On Thu, Mar 18, 2010 at 05:54:13PM -0700, David Miller wrote:
> From: Tejun Heo <tj@kernel.org>
> Date: Thu, 18 Mar 2010 18:30:34 +0900
> 
> >  
> >  	if (!total_profile_count) {
> > -		buf = (char *)alloc_percpu(perf_trace_t);
> > +		buf = (char *)__alloc_percpu(sizeof(perf_trace_t),
> > +					     __alignof__(unsigned long));
> >  		if (!buf)
> >  			goto fail_buf;
> 
> Why not make perf_trace_t have the proper alignment?


So, making perf_trace_t as align(8) would do the trick?
I lack the knowledge about alignment layout for archs that
need aligned accesses.
At a first glance, what I would except is that every buffer
has a base address aligned, no?


> 
> That's better than patching around it like this.
> 
> Defining it as an array of char[]'s is just asking
> for lots of trouble.


Yeah but we need a generic type. This is because
our buffer can be of any random type to match all
the trace event layouts we have, all of them being
generated by macros.