Re: [PATCH UPDATED 12/35] workqueue: update cwq alignement
From: Frederic Weisbecker
Date: Tue Jun 29 2010 - 09:38:55 EST
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@xxxxxxxxxx>
> Cc: Christoph Lameter <cl@xxxxxxxxxxxxxxxxxxxx>
> Cc: Ingo Molnar <mingo@xxxxxxx>
> Cc: Frederic Weisbecker <fweisbec@xxxxxxxxx>
> Reported-by: Michal Simek <michal.simek@xxxxxxxxxxxxx>
Your tree now builds well on x86-32. Thanks!
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