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Date: Mon, 25 May 2009 11:09:43 +0200
From: Jan Kara <jack@...e.cz>
To: Jens Axboe <jens.axboe@...cle.com>
Cc: linux-kernel@...r.kernel.org, linux-fsdevel@...r.kernel.org,
chris.mason@...cle.com, david@...morbit.com, hch@...radead.org,
akpm@...ux-foundation.org, jack@...e.cz,
yanmin_zhang@...ux.intel.com
Subject: Re: [PATCH 05/13] aio: mostly crap
On Mon 25-05-09 09:30:52, Jens Axboe wrote:
> First attempts at getting rid of some locking in aio
I suppose this shouldn't be in the series ;).
Honza
> Signed-off-by: Jens Axboe <jens.axboe@...cle.com>
> ---
> fs/aio.c | 151 +++++++++++++++++++++++++++++++++------------------
> include/linux/aio.h | 11 ++--
> 2 files changed, 103 insertions(+), 59 deletions(-)
>
> diff --git a/fs/aio.c b/fs/aio.c
> index 76da125..98c82f2 100644
> --- a/fs/aio.c
> +++ b/fs/aio.c
> @@ -79,9 +79,8 @@ static int __init aio_setup(void)
> return 0;
> }
>
> -static void aio_free_ring(struct kioctx *ctx)
> +static void __aio_free_ring(struct kioctx *ctx, struct aio_ring_info *info)
> {
> - struct aio_ring_info *info = &ctx->ring_info;
> long i;
>
> for (i=0; i<info->nr_pages; i++)
> @@ -99,16 +98,28 @@ static void aio_free_ring(struct kioctx *ctx)
> info->nr = 0;
> }
>
> -static int aio_setup_ring(struct kioctx *ctx)
> +static void aio_free_ring(struct kioctx *ctx)
> +{
> + unsigned int i;
> +
> + for_each_possible_cpu(i) {
> + struct aio_ring_info *info = per_cpu_ptr(ctx->ring_info, i);
> +
> + __aio_free_ring(ctx, info);
> + }
> + free_percpu(ctx->ring_info);
> + ctx->ring_info = NULL;
> +}
> +
> +static int __aio_setup_ring(struct kioctx *ctx, struct aio_ring_info *info)
> {
> struct aio_ring *ring;
> - struct aio_ring_info *info = &ctx->ring_info;
> unsigned nr_events = ctx->max_reqs;
> unsigned long size;
> int nr_pages;
>
> - /* Compensate for the ring buffer's head/tail overlap entry */
> - nr_events += 2; /* 1 is required, 2 for good luck */
> + /* round nr_event to next power of 2 */
> + nr_events = roundup_pow_of_two(nr_events);
>
> size = sizeof(struct aio_ring);
> size += sizeof(struct io_event) * nr_events;
> @@ -117,8 +128,6 @@ static int aio_setup_ring(struct kioctx *ctx)
> if (nr_pages < 0)
> return -EINVAL;
>
> - nr_events = (PAGE_SIZE * nr_pages - sizeof(struct aio_ring)) / sizeof(struct io_event);
> -
> info->nr = 0;
> info->ring_pages = info->internal_pages;
> if (nr_pages > AIO_RING_PAGES) {
> @@ -158,7 +167,8 @@ static int aio_setup_ring(struct kioctx *ctx)
> ring = kmap_atomic(info->ring_pages[0], KM_USER0);
> ring->nr = nr_events; /* user copy */
> ring->id = ctx->user_id;
> - ring->head = ring->tail = 0;
> + atomic_set(&ring->head, 0);
> + ring->tail = 0;
> ring->magic = AIO_RING_MAGIC;
> ring->compat_features = AIO_RING_COMPAT_FEATURES;
> ring->incompat_features = AIO_RING_INCOMPAT_FEATURES;
> @@ -168,6 +178,27 @@ static int aio_setup_ring(struct kioctx *ctx)
> return 0;
> }
>
> +static int aio_setup_ring(struct kioctx *ctx)
> +{
> + unsigned int i;
> + int ret;
> +
> + ctx->ring_info = alloc_percpu(struct aio_ring_info);
> + if (!ctx->ring_info)
> + return -ENOMEM;
> +
> + ret = 0;
> + for_each_possible_cpu(i) {
> + struct aio_ring_info *info = per_cpu_ptr(ctx->ring_info, i);
> + int err;
> +
> + err = __aio_setup_ring(ctx, info);
> + if (err && !ret)
> + ret = err;
> + }
> +
> + return ret;
> +}
>
> /* aio_ring_event: returns a pointer to the event at the given index from
> * kmap_atomic(, km). Release the pointer with put_aio_ring_event();
> @@ -176,8 +207,8 @@ static int aio_setup_ring(struct kioctx *ctx)
> #define AIO_EVENTS_FIRST_PAGE ((PAGE_SIZE - sizeof(struct aio_ring)) / sizeof(struct io_event))
> #define AIO_EVENTS_OFFSET (AIO_EVENTS_PER_PAGE - AIO_EVENTS_FIRST_PAGE)
>
> -#define aio_ring_event(info, nr, km) ({ \
> - unsigned pos = (nr) + AIO_EVENTS_OFFSET; \
> +#define aio_ring_event(info, __nr, km) ({ \
> + unsigned pos = ((__nr) & ((info)->nr - 1)) + AIO_EVENTS_OFFSET; \
> struct io_event *__event; \
> __event = kmap_atomic( \
> (info)->ring_pages[pos / AIO_EVENTS_PER_PAGE], km); \
> @@ -262,7 +293,6 @@ static struct kioctx *ioctx_alloc(unsigned nr_events)
>
> atomic_set(&ctx->users, 1);
> spin_lock_init(&ctx->ctx_lock);
> - spin_lock_init(&ctx->ring_info.ring_lock);
> init_waitqueue_head(&ctx->wait);
>
> INIT_LIST_HEAD(&ctx->active_reqs);
> @@ -426,6 +456,7 @@ void exit_aio(struct mm_struct *mm)
> static struct kiocb *__aio_get_req(struct kioctx *ctx)
> {
> struct kiocb *req = NULL;
> + struct aio_ring_info *info;
> struct aio_ring *ring;
> int okay = 0;
>
> @@ -448,15 +479,18 @@ static struct kiocb *__aio_get_req(struct kioctx *ctx)
> /* Check if the completion queue has enough free space to
> * accept an event from this io.
> */
> - spin_lock_irq(&ctx->ctx_lock);
> - ring = kmap_atomic(ctx->ring_info.ring_pages[0], KM_USER0);
> - if (ctx->reqs_active < aio_ring_avail(&ctx->ring_info, ring)) {
> + local_irq_disable();
> + info = per_cpu_ptr(ctx->ring_info, smp_processor_id());
> + ring = kmap_atomic(info->ring_pages[0], KM_IRQ0);
> + if (ctx->reqs_active < aio_ring_avail(info, ring)) {
> + spin_lock(&ctx->ctx_lock);
> list_add(&req->ki_list, &ctx->active_reqs);
> ctx->reqs_active++;
> + spin_unlock(&ctx->ctx_lock);
> okay = 1;
> }
> - kunmap_atomic(ring, KM_USER0);
> - spin_unlock_irq(&ctx->ctx_lock);
> + kunmap_atomic(ring, KM_IRQ0);
> + local_irq_enable();
>
> if (!okay) {
> kmem_cache_free(kiocb_cachep, req);
> @@ -578,9 +612,11 @@ int aio_put_req(struct kiocb *req)
> {
> struct kioctx *ctx = req->ki_ctx;
> int ret;
> +
> spin_lock_irq(&ctx->ctx_lock);
> ret = __aio_put_req(ctx, req);
> spin_unlock_irq(&ctx->ctx_lock);
> +
> return ret;
> }
>
> @@ -954,7 +990,7 @@ int aio_complete(struct kiocb *iocb, long res, long res2)
> struct aio_ring *ring;
> struct io_event *event;
> unsigned long flags;
> - unsigned long tail;
> + unsigned tail;
> int ret;
>
> /*
> @@ -972,15 +1008,14 @@ int aio_complete(struct kiocb *iocb, long res, long res2)
> return 1;
> }
>
> - info = &ctx->ring_info;
> -
> /* add a completion event to the ring buffer.
> * must be done holding ctx->ctx_lock to prevent
> * other code from messing with the tail
> * pointer since we might be called from irq
> * context.
> */
> - spin_lock_irqsave(&ctx->ctx_lock, flags);
> + local_irq_save(flags);
> + info = per_cpu_ptr(ctx->ring_info, smp_processor_id());
>
> if (iocb->ki_run_list.prev && !list_empty(&iocb->ki_run_list))
> list_del_init(&iocb->ki_run_list);
> @@ -996,8 +1031,6 @@ int aio_complete(struct kiocb *iocb, long res, long res2)
>
> tail = info->tail;
> event = aio_ring_event(info, tail, KM_IRQ0);
> - if (++tail >= info->nr)
> - tail = 0;
>
> event->obj = (u64)(unsigned long)iocb->ki_obj.user;
> event->data = iocb->ki_user_data;
> @@ -1013,13 +1046,14 @@ int aio_complete(struct kiocb *iocb, long res, long res2)
> */
> smp_wmb(); /* make event visible before updating tail */
>
> + tail++;
> info->tail = tail;
> ring->tail = tail;
>
> put_aio_ring_event(event, KM_IRQ0);
> kunmap_atomic(ring, KM_IRQ1);
>
> - pr_debug("added to ring %p at [%lu]\n", iocb, tail);
> + pr_debug("added to ring %p at [%u]\n", iocb, tail);
>
> /*
> * Check if the user asked us to deliver the result through an
> @@ -1031,7 +1065,9 @@ int aio_complete(struct kiocb *iocb, long res, long res2)
>
> put_rq:
> /* everything turned out well, dispose of the aiocb. */
> + spin_lock(&ctx->ctx_lock);
> ret = __aio_put_req(ctx, iocb);
> + spin_unlock(&ctx->ctx_lock);
>
> /*
> * We have to order our ring_info tail store above and test
> @@ -1044,49 +1080,58 @@ put_rq:
> if (waitqueue_active(&ctx->wait))
> wake_up(&ctx->wait);
>
> - spin_unlock_irqrestore(&ctx->ctx_lock, flags);
> + local_irq_restore(flags);
> + return ret;
> +}
> +
> +static int __aio_read_evt(struct aio_ring_info *info, struct aio_ring *ring,
> + struct io_event *ent)
> +{
> + struct io_event *evp;
> + unsigned head;
> + int ret = 0;
> +
> + do {
> + head = atomic_read(&ring->head);
> + if (head == ring->tail)
> + break;
> + evp = aio_ring_event(info, head, KM_USER1);
> + *ent = *evp;
> + smp_mb(); /* finish reading the event before updatng the head */
> + ++ret;
> + put_aio_ring_event(evp, KM_USER1);
> + } while (head != atomic_cmpxchg(&ring->head, head, head + 1));
> +
> return ret;
> }
>
> /* aio_read_evt
> * Pull an event off of the ioctx's event ring. Returns the number of
> * events fetched (0 or 1 ;-)
> - * FIXME: make this use cmpxchg.
> - * TODO: make the ringbuffer user mmap()able (requires FIXME).
> + * TODO: make the ringbuffer user mmap()able
> */
> static int aio_read_evt(struct kioctx *ioctx, struct io_event *ent)
> {
> - struct aio_ring_info *info = &ioctx->ring_info;
> - struct aio_ring *ring;
> - unsigned long head;
> - int ret = 0;
> + int i, ret = 0;
>
> - ring = kmap_atomic(info->ring_pages[0], KM_USER0);
> - dprintk("in aio_read_evt h%lu t%lu m%lu\n",
> - (unsigned long)ring->head, (unsigned long)ring->tail,
> - (unsigned long)ring->nr);
> + for_each_possible_cpu(i) {
> + struct aio_ring_info *info;
> + struct aio_ring *ring;
>
> - if (ring->head == ring->tail)
> - goto out;
> + info = per_cpu_ptr(ioctx->ring_info, i);
> + ring = kmap_atomic(info->ring_pages[0], KM_USER0);
> + dprintk("in aio_read_evt h%u t%u m%u\n",
> + atomic_read(&ring->head), ring->tail, ring->nr);
>
> - spin_lock(&info->ring_lock);
> -
> - head = ring->head % info->nr;
> - if (head != ring->tail) {
> - struct io_event *evp = aio_ring_event(info, head, KM_USER1);
> - *ent = *evp;
> - head = (head + 1) % info->nr;
> - smp_mb(); /* finish reading the event before updatng the head */
> - ring->head = head;
> - ret = 1;
> - put_aio_ring_event(evp, KM_USER1);
> + ret = __aio_read_evt(info, ring, ent);
> + kunmap_atomic(ring, KM_USER0);
> + if (ret)
> + break;
> }
> - spin_unlock(&info->ring_lock);
>
> -out:
> - kunmap_atomic(ring, KM_USER0);
> - dprintk("leaving aio_read_evt: %d h%lu t%lu\n", ret,
> - (unsigned long)ring->head, (unsigned long)ring->tail);
> + dprintk("leaving aio_read_evt: %d h%u t%u\n", ret,
> + atomic_read(&ring->head), ring->tail);
> +
> return ret;
> }
>
> diff --git a/include/linux/aio.h b/include/linux/aio.h
> index b16a957..9a7acb4 100644
> --- a/include/linux/aio.h
> +++ b/include/linux/aio.h
> @@ -149,7 +149,7 @@ struct kiocb {
> struct aio_ring {
> unsigned id; /* kernel internal index number */
> unsigned nr; /* number of io_events */
> - unsigned head;
> + atomic_t head;
> unsigned tail;
>
> unsigned magic;
> @@ -157,11 +157,11 @@ struct aio_ring {
> unsigned incompat_features;
> unsigned header_length; /* size of aio_ring */
>
> -
> - struct io_event io_events[0];
> + struct io_event io_events[0];
> }; /* 128 bytes + ring size */
>
> -#define aio_ring_avail(info, ring) (((ring)->head + (info)->nr - 1 - (ring)->tail) % (info)->nr)
> +#define aio_ring_avail(info, ring) \
> + ((info)->nr + (unsigned) atomic_read(&(ring)->head) - (ring)->tail)
>
> #define AIO_RING_PAGES 8
> struct aio_ring_info {
> @@ -169,7 +169,6 @@ struct aio_ring_info {
> unsigned long mmap_size;
>
> struct page **ring_pages;
> - spinlock_t ring_lock;
> long nr_pages;
>
> unsigned nr, tail;
> @@ -197,7 +196,7 @@ struct kioctx {
> /* sys_io_setup currently limits this to an unsigned int */
> unsigned max_reqs;
>
> - struct aio_ring_info ring_info;
> + struct aio_ring_info *ring_info;
>
> struct delayed_work wq;
>
> --
> 1.6.3.rc0.1.gf800
>
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