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

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Message-ID: <4BA2D8A4.2080409@kernel.org>
Date:	Fri, 19 Mar 2010 10:51:32 +0900
From:	Tejun Heo <tj@...nel.org>
To:	Frederic Weisbecker <fweisbec@...il.com>
CC:	David Miller <davem@...emloft.net>, sparclinux@...r.kernel.org,
	linux-kernel@...r.kernel.org
Subject: Re: [BUG] percpu misaligned allocation

Hello,

On 03/19/2010 10:31 AM, Frederic Weisbecker wrote:
> 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?

Sure, I just wanted to verify the cause of the problem.

> 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.

If you can't make it a proper type, __alignof__(unsigned long long)
would be better.

> 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.

I hope those macros align properly according to types.

Thanks.

-- 
tejun
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