linux-kernel - Re: [PATCH UPDATED 12/35] workqueue: update cwq alignement

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Message-ID: <20100629133858.GC5318@nowhere>
Date:	Tue, 29 Jun 2010 15:39:01 +0200
From:	Frederic Weisbecker <fweisbec@...il.com>
To:	Tejun Heo <tj@...nel.org>
Cc:	torvalds@...ux-foundation.org, mingo@...e.hu,
	linux-kernel@...r.kernel.org, jeff@...zik.org,
	akpm@...ux-foundation.org, rusty@...tcorp.com.au,
	cl@...ux-foundation.org, dhowells@...hat.com,
	arjan@...ux.intel.com, oleg@...hat.com, axboe@...nel.dk,
	dwalker@...eaurora.org, stefanr@...6.in-berlin.de,
	florian@...kler.org, andi@...stfloor.org, mst@...hat.com,
	randy.dunlap@...cle.com
Subject: Re: [PATCH UPDATED 12/35] workqueue: update cwq alignement

On Tue, Jun 29, 2010 at 10:12:13AM +0200, Tejun Heo wrote:
> work->data field is used for two purposes.  It points to cwq it's
> queued on and the lower bits are used for flags.  Currently, two bits
> are reserved which is always safe as 4 byte alignment is guaranteed on
> every architecture.  However, future changes will need more flag bits.
> 
> On SMP, the percpu allocator is capable of honoring larger alignment
> (there are other users which depend on it) and larger alignment works
> just fine.  On UP, percpu allocator is a thin wrapper around
> kzalloc/kfree() and don't honor alignment request.
> 
> This patch introduces WORK_STRUCT_FLAG_BITS and implements
> alloc/free_cwqs() which guarantees max(1 << WORK_STRUCT_FLAG_BITS,
> __alignof__(unsigned long long) alignment both on SMP and UP.  On SMP,
> simply wrapping percpu allocator is enough.  On UP, extra space is
> allocated so that cwq can be aligned and the original pointer can be
> stored after it which is used in the free path.
> 
> * Alignment problem on UP is reported by Michal Simek.
> 
> Signed-off-by: Tejun Heo <tj@...nel.org>
> Cc: Christoph Lameter <cl@...ux-foundation.org>
> Cc: Ingo Molnar <mingo@...e.hu>
> Cc: Frederic Weisbecker <fweisbec@...il.com>
> Reported-by: Michal Simek <michal.simek@...alogix.com>
> ---



Your tree now builds well on x86-32. Thanks!

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