linux-kernel - Re: [PATCH] MN10300: Fix the PERCPU() alignment to allow for workqueues

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Message-ID: <4CC6EC31.4090304@kernel.org>
Date:	Tue, 26 Oct 2010 16:56:49 +0200
From:	Tejun Heo <tj@...nel.org>
To:	David Howells <dhowells@...hat.com>
CC:	torvalds@...l.org, akpm@...ux-foundation.org,
	linux-am33-list@...hat.com, linux-kernel@...r.kernel.org,
	Akira Takeuchi <takeuchi.akr@...panasonic.com>,
	Mark Salter <msalter@...hat.com>
Subject: Re: [PATCH] MN10300: Fix the PERCPU() alignment to allow for workqueues

Hello, David.

On 10/26/2010 04:50 PM, David Howells wrote:
>>> FRV's page size is 16KB, so on that we really don't want it to be
>>> PAGE_SIZE.
>>
>> Why not?  It's in the init section which will be freed anyway and with
>> the kernel image compression it's not even gonna add any noticeable
>> amount to the kernel image size.  There isn't any benefit in using
>> anything smaller than PAGE_SIZE for alignment.  Also, percpu allocator
>> guarantees alignment requirement upto PAGE_SIZE is honored.  If the
>> output section uses smaller alignment, the percpu AS will end up being
>> misaligned.
> 
> The bootloader we have doesn't do decompression.

I see.  :-(

> On the other hand, does the PERCPU stuff need to be allocated space
> in the image by the linker?  Can it be initialised to anything other
> than zeros?

Sure, for example, in kernel/timer.c.

  static DEFINE_PER_CPU(struct tvec_base *, tvec_bases) = &boot_tvec_bases;

It doesn't seem too popular at this point tho.

Thanks.

-- 
tejun
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