linux-kernel - Re: [PATCH] perf core: Get rid of 'uses dynamic stack allocation' warning

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Message-ID: <56A1E301.2080409@huawei.com>
Date:	Fri, 22 Jan 2016 16:06:25 +0800
From:	"Wangnan (F)" <wangnan0@...wei.com>
To:	Peter Zijlstra <peterz@...radead.org>
CC:	<linux-kernel@...r.kernel.org>, <pi3orama@....com>
Subject: Re: [PATCH] perf core: Get rid of 'uses dynamic stack allocation'
 warning



On 2016/1/22 16:00, Peter Zijlstra wrote:
> On Fri, Jan 22, 2016 at 06:52:01AM +0000, Wang Nan wrote:
>> On s390 with CONFIG_WARN_DYNAMIC_STACK set, 'uses dynamic stack
>> allocation' warning is issued when defining 'struct perf_sample_data'
>> local variable.
>>
>> This patch suppress this warning by allocating extra 255 bytes and
>> compute aligned pointer manually.
> I've seen the warning and always wondered wtf it was about. This
> Changelog doesn't actually explain what the problem is, so I cannot
> judge the solution.
>
> That said, 255 extra bytes does sound excessive just to avoid a warn.

OK. Then I happly ignore it.

I also don't know the exact reason.  I guess it related
to the ____cacheline_aligned decorator after 'struct
perf_sample_data'. When allocating that structure on the
stack, kernel has to dynamically compute the stack size it
need to satisify the alignment constrain. My patch does
this work manually.

Thank you.