linux-kernel - Re: [BUG] percpu misaligned allocation

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Message-ID: <20100319013119.GB22095@nowhere>
Date:	Fri, 19 Mar 2010 02:31:22 +0100
From:	Frederic Weisbecker <fweisbec@...il.com>
To:	David Miller <davem@...emloft.net>
Cc:	tj@...nel.org, sparclinux@...r.kernel.org,
	linux-kernel@...r.kernel.org
Subject: Re: [BUG] percpu misaligned allocation

On Thu, Mar 18, 2010 at 05:54:13PM -0700, David Miller wrote:
> From: Tejun Heo <tj@...nel.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.

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