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Message-ID: <4B164D48.1040508@petalogix.com>
Date: Wed, 02 Dec 2009 12:19:36 +0100
From: Michal Simek <michal.simek@...alogix.com>
To: Tejun Heo <tj@...nel.org>
CC: Ingo Molnar <mingo@...e.hu>,
Christoph Lameter <cl@...ux-foundation.org>,
Stephen Rothwell <sfr@...b.auug.org.au>,
linux-next@...r.kernel.org, LKML <linux-kernel@...r.kernel.org>,
Rusty Russell <rusty@...tcorp.com.au>
Subject: Re: problems in linux-next (Was: Re: linux-next: Tree for December
1)
Hi Tejun,
Tejun Heo wrote:
> Hello,
>
> It will look like the following.
I have problem to apply your patch against Stephens next tree. Which tree do you use?
Thanks,
Michal
[monstr@...ebook linux-next]$ git reset --hard next-20091201
HEAD is now at 16aa569 Add linux-next specific files for 20091201
[monstr@...ebook linux-next]$ git-am < problems\ in\ linux-next\ \(Was\:\ Re\:\ linux-next\:\ Tree\
for\ December\ 1\).eml
previous dotest directory .dotest still exists but mbox given.
[monstr@...ebook linux-next]$ rm -rf .dotest/
[monstr@...ebook linux-next]$ git-am < problems\ in\ linux-next\ \(Was\:\ Re\:\ linux-next\:\ Tree\
for\ December\ 1\).eml
Applying problems in linux-next (Was: Re: linux-next: Tree for December 1)
error: patch failed: include/linux/workqueue.h:29
error: include/linux/workqueue.h: patch does not apply
error: patch failed: kernel/workqueue.c:46
error: kernel/workqueue.c: patch does not apply
Patch failed at 0001.
When you have resolved this problem run "git-am --resolved".
If you would prefer to skip this patch, instead run "git-am --skip".
[monstr@...ebook linux-next]$ git-am < problems\ in\ linux-next\ \(Was\:\ Re\:\ linux-next\:\ Tree\
for\ December\ 1\).eml
Applying problems in linux-next (Was: Re: linux-next: Tree for December 1)
error: patch failed: include/linux/workqueue.h:29
error: include/linux/workqueue.h: patch does not apply
error: patch failed: kernel/workqueue.c:46
error: kernel/workqueue.c: patch does not apply
Patch failed at 0001.
When you have resolved this problem run "git-am --resolved".
If you would prefer to skip this patch, instead run "git-am --skip".
>
> Thanks.
>
> =========================================================================
> Subject: workqueue: update cwq alignement
>
> 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, aligns cwqs accordingly
> and implements alloc/free_cwqs() which guarantees the alignment both
> on SMP and UP. On SMP, simply wrapping percpu allocator is enouhg.
> 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.
>
> While at it, as cwqs are now forced aligned, make sure the resulting
> alignment is at least equal to or larger than that of long long.
>
> Signed-off-by: Tejun Heo <tj@...nel.org>
> Cc: Christoph Lameter <cl@...ux-foundation.org>
> Cc: Ingo Molnar <mingo@...e.hu>
> ---
> include/linux/workqueue.h | 4 ++-
> kernel/workqueue.c | 58 ++++++++++++++++++++++++++++++++++++++++++----
> 2 files changed, 56 insertions(+), 6 deletions(-)
>
> Index: work/include/linux/workqueue.h
> ===================================================================
> --- work.orig/include/linux/workqueue.h
> +++ work/include/linux/workqueue.h
> @@ -29,7 +29,9 @@ enum {
> WORK_STRUCT_PENDING = 1 << WORK_STRUCT_PENDING_BIT,
> WORK_STRUCT_STATIC = 1 << WORK_STRUCT_STATIC_BIT,
>
> - WORK_STRUCT_FLAG_MASK = 3UL,
> + WORK_STRUCT_FLAG_BITS = 2,
> +
> + WORK_STRUCT_FLAG_MASK = (1UL << WORK_STRUCT_FLAG_BITS) - 1,
> WORK_STRUCT_WQ_DATA_MASK = ~WORK_STRUCT_FLAG_MASK,
> };
>
> Index: work/kernel/workqueue.c
> ===================================================================
> --- work.orig/kernel/workqueue.c
> +++ work/kernel/workqueue.c
> @@ -46,7 +46,9 @@
>
> /*
> * The per-CPU workqueue (if single thread, we always use the first
> - * possible cpu).
> + * possible cpu). The lower WORK_STRUCT_FLAG_BITS of
> + * work_struct->data are used for flags and thus cwqs need to be
> + * aligned at two's power of the number of flag bits.
> */
> struct cpu_workqueue_struct {
>
> @@ -58,7 +60,7 @@ struct cpu_workqueue_struct {
>
> struct workqueue_struct *wq; /* I: the owning workqueue */
> struct task_struct *thread;
> -} ____cacheline_aligned;
> +} __attribute__((aligned(1 << WORK_STRUCT_FLAG_BITS)));
>
> /*
> * The externally visible workqueue abstraction is an array of
> @@ -932,6 +934,44 @@ int current_is_keventd(void)
>
> }
>
> +static struct cpu_workqueue_struct *alloc_cwqs(void)
> +{
> + const size_t size = sizeof(struct cpu_workqueue_struct);
> + const size_t align = __alignof__(struct cpu_workqueue_struct);
> + 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
> + /* On SMP, percpu allocator can do it itself */
> + cwqs = __alloc_percpu(size, align);
> +#endif
> + /* just in case, make sure it's actually aligned */
> + BUG_ON(!IS_ALIGNED((unsigned long)cwqs, align));
> + return cwqs;
> +}
> +
> +static void free_cwqs(struct cpu_workqueue_struct *cwqs)
> +{
> +#ifndef CONFIG_SMP
> + /* on UP, the pointer to free is stored right after the cwq */
> + if (cwqs)
> + free_percpu(*(void **)per_cpu_ptr(cwqs + 1, 0));
> +#else
> + free_percpu(cwqs);
> +#endif
> +}
> +
> static int create_workqueue_thread(struct cpu_workqueue_struct *cwq, int cpu)
> {
> struct workqueue_struct *wq = cwq->wq;
> @@ -977,7 +1017,7 @@ struct workqueue_struct *__create_workqu
> if (!wq)
> goto err;
>
> - wq->cpu_wq = alloc_percpu(struct cpu_workqueue_struct);
> + wq->cpu_wq = alloc_cwqs();
> if (!wq->cpu_wq)
> goto err;
>
> @@ -1023,7 +1063,7 @@ struct workqueue_struct *__create_workqu
> return wq;
> err:
> if (wq) {
> - free_percpu(wq->cpu_wq);
> + free_cwqs(wq->cpu_wq);
> kfree(wq);
> }
> return NULL;
> @@ -1074,7 +1114,7 @@ void destroy_workqueue(struct workqueue_
> for_each_possible_cpu(cpu)
> cleanup_workqueue_thread(get_cwq(cpu, wq));
>
> - free_percpu(wq->cpu_wq);
> + free_cwqs(wq->cpu_wq);
> kfree(wq);
> }
> EXPORT_SYMBOL_GPL(destroy_workqueue);
> @@ -1163,6 +1203,14 @@ EXPORT_SYMBOL_GPL(work_on_cpu);
>
> void __init init_workqueues(void)
> {
> + /*
> + * cwqs are forced aligned according to WORK_STRUCT_FLAG_BITS.
> + * Make sure that the alignment isn't lower than that of
> + * unsigned long long.
> + */
> + BUILD_BUG_ON(__alignof__(struct cpu_workqueue_struct) <
> + __alignof__(unsigned long long));
> +
> singlethread_cpu = cpumask_first(cpu_possible_mask);
> hotcpu_notifier(workqueue_cpu_callback, 0);
> keventd_wq = create_workqueue("events");
--
Michal Simek, Ing. (M.Eng)
PetaLogix - Linux Solutions for a Reconfigurable World
w: www.petalogix.com p: +61-7-30090663,+42-0-721842854 f: +61-7-30090663
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