linux-kernel - Re: [PATCH 17/43] workqueue: update cwq alignement

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Message-ID: <20100228171255.GA20167@redhat.com>
Date:	Sun, 28 Feb 2010 18:12:55 +0100
From:	Oleg Nesterov <oleg@...hat.com>
To:	Tejun Heo <tj@...nel.org>
Cc:	torvalds@...ux-foundation.org, mingo@...e.hu, peterz@...radead.org,
	awalls@...ix.net, linux-kernel@...r.kernel.org, jeff@...zik.org,
	akpm@...ux-foundation.org, jens.axboe@...cle.com,
	rusty@...tcorp.com.au, cl@...ux-foundation.org,
	dhowells@...hat.com, arjan@...ux.intel.com, avi@...hat.com,
	johannes@...solutions.net, andi@...stfloor.org
Subject: Re: [PATCH 17/43] workqueue: update cwq alignement

On 02/26, Tejun Heo wrote:
>
> +static struct cpu_workqueue_struct *alloc_cwqs(void)
> +{
> +	const size_t size = sizeof(struct cpu_workqueue_struct);
> +	const size_t align = 1 << WORK_STRUCT_FLAG_BITS;
> +	struct cpu_workqueue_struct *cwqs;
> +#ifndef CONFIG_SMP
> +	void *ptr;
> +
> +	/*
> +	 * On UP, percpu allocator doesn't honor alignment parameter
> +	 * and simply uses arch-dependent default.  Allocate enough
> +	 * room to align cwq and put an extra pointer at the end
> +	 * pointing back to the originally allocated pointer which
> +	 * will be used for free.
> +	 */
> +	ptr = __alloc_percpu(size + align + sizeof(void *), 1);
> +	cwqs = PTR_ALIGN(ptr, align);
> +	*(void **)per_cpu_ptr(cwqs + 1, 0) = ptr;
> +#else

Nice trick, but perhaps it would be more simple/clear to just add
"void *my_memory" into cpu_workqueue_struct, under !CONFIG_SMP ?

Oleg.

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