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Subject[PATCH 14/32] aio: Make aio_read_evt() more efficient, convert to hrtimers
Date
Previously, aio_read_event() pulled a single completion off the
ringbuffer at a time, locking and unlocking each time. Changed it to
pull off as many events as it can at a time, and copy them directly to
userspace.

This also fixes a bug where if copying the event to userspace failed,
we'd lose the event.

Also convert it to wait_event_interruptible_hrtimeout(), which
simplifies it quite a bit.

v3: Convert to wait_event_interupttible_hrtimeout()
v2: Move finish_wait() call so we're not calling copy_to_user in
TASK_INTERRUPTIBLE state
v2: Restructure the code so we're not calling prepare_to_wait() until
after we've done everything that might block, also got rid of the
separate fast path

Signed-off-by: Kent Overstreet <koverstreet@google.com>
---
fs/aio.c | 228 ++++++++++++++++++++++-----------------------------------------
1 file changed, 78 insertions(+), 150 deletions(-)

diff --git a/fs/aio.c b/fs/aio.c
index e0eb23d..06e1dd0 100644
--- a/fs/aio.c
+++ b/fs/aio.c
@@ -63,7 +63,7 @@ struct aio_ring_info {
unsigned long mmap_size;

struct page **ring_pages;
- spinlock_t ring_lock;
+ struct mutex ring_lock;
long nr_pages;

unsigned nr, tail;
@@ -341,7 +341,7 @@ static struct kioctx *ioctx_alloc(unsigned nr_events)
atomic_set(&ctx->users, 2);
atomic_set(&ctx->dead, 0);
spin_lock_init(&ctx->ctx_lock);
- spin_lock_init(&ctx->ring_info.ring_lock);
+ mutex_init(&ctx->ring_info.ring_lock);
init_waitqueue_head(&ctx->wait);

INIT_LIST_HEAD(&ctx->active_reqs);
@@ -744,187 +744,115 @@ put_rq:
}
EXPORT_SYMBOL(aio_complete);

-/* 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).
+/* aio_read_events
+ * Pull an event off of the ioctx's event ring. Returns the number of
+ * events fetched
*/
-static int aio_read_evt(struct kioctx *ioctx, struct io_event *ent)
+static int aio_read_events_ring(struct kioctx *ctx,
+ struct io_event __user *event, long nr)
{
- struct aio_ring_info *info = &ioctx->ring_info;
+ struct aio_ring_info *info = &ctx->ring_info;
struct aio_ring *ring;
- unsigned long head;
- int ret = 0;
+ unsigned head, pos;
+ int ret = 0, copy_ret;
+
+ if (!mutex_trylock(&info->ring_lock)) {
+ __set_current_state(TASK_RUNNING);
+ mutex_lock(&info->ring_lock);
+ }

ring = kmap_atomic(info->ring_pages[0]);
- pr_debug("h%u t%u m%u\n", ring->head, ring->tail, ring->nr);
+ head = ring->head;
+ kunmap_atomic(ring);
+
+ pr_debug("h%u t%u m%u\n", head, info->tail, info->nr);

- if (ring->head == ring->tail)
+ if (head == info->tail)
goto out;

- spin_lock(&info->ring_lock);
-
- head = ring->head % info->nr;
- if (head != ring->tail) {
- struct io_event *evp = aio_ring_event(info, head);
- *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);
+ __set_current_state(TASK_RUNNING);
+
+ while (ret < nr) {
+ unsigned i = (head < info->tail ? info->tail : info->nr) - head;
+ struct io_event *ev;
+ struct page *page;
+
+ if (head == info->tail)
+ break;
+
+ i = min_t(int, i, nr - ret);
+ i = min_t(int, i, AIO_EVENTS_PER_PAGE -
+ ((head + AIO_EVENTS_OFFSET) % AIO_EVENTS_PER_PAGE));
+
+ pos = head + AIO_EVENTS_OFFSET;
+ page = info->ring_pages[pos / AIO_EVENTS_PER_PAGE];
+ pos %= AIO_EVENTS_PER_PAGE;
+
+ ev = kmap(page);
+ copy_ret = copy_to_user(event + ret, ev + pos, sizeof(*ev) * i);
+ kunmap(page);
+
+ if (unlikely(copy_ret)) {
+ ret = -EFAULT;
+ goto out;
+ }
+
+ ret += i;
+ head += i;
+ head %= info->nr;
}
- spin_unlock(&info->ring_lock);

-out:
+ ring = kmap_atomic(info->ring_pages[0]);
+ ring->head = head;
kunmap_atomic(ring);
- pr_debug("%d h%u t%u\n", ret, ring->head, ring->tail);
+
+ pr_debug("%d h%u t%u\n", ret, head, info->tail);
+out:
+ mutex_unlock(&info->ring_lock);
+
return ret;
}

-struct aio_timeout {
- struct timer_list timer;
- int timed_out;
- struct task_struct *p;
-};
-
-static void timeout_func(unsigned long data)
+static bool aio_read_events(struct kioctx *ctx, long min_nr, long nr,
+ struct io_event __user *event, long *i)
{
- struct aio_timeout *to = (struct aio_timeout *)data;
+ long ret = aio_read_events_ring(ctx, event + *i, nr - *i);

- to->timed_out = 1;
- wake_up_process(to->p);
-}
+ if (ret > 0)
+ *i += ret;

-static inline void init_timeout(struct aio_timeout *to)
-{
- setup_timer_on_stack(&to->timer, timeout_func, (unsigned long) to);
- to->timed_out = 0;
- to->p = current;
-}
+ if (unlikely(atomic_read(&ctx->dead)))
+ ret = -EINVAL;

-static inline void set_timeout(long start_jiffies, struct aio_timeout *to,
- const struct timespec *ts)
-{
- to->timer.expires = start_jiffies + timespec_to_jiffies(ts);
- if (time_after(to->timer.expires, jiffies))
- add_timer(&to->timer);
- else
- to->timed_out = 1;
-}
+ if (!*i)
+ *i = ret;

-static inline void clear_timeout(struct aio_timeout *to)
-{
- del_singleshot_timer_sync(&to->timer);
+ return ret < 0 || *i >= min_nr;
}

-static int read_events(struct kioctx *ctx,
- long min_nr, long nr,
+static long read_events(struct kioctx *ctx, long min_nr, long nr,
struct io_event __user *event,
struct timespec __user *timeout)
{
- long start_jiffies = jiffies;
- struct task_struct *tsk = current;
- DECLARE_WAITQUEUE(wait, tsk);
- int ret;
- int i = 0;
- struct io_event ent;
- struct aio_timeout to;
-
- /* needed to zero any padding within an entry (there shouldn't be
- * any, but C is fun!
- */
- memset(&ent, 0, sizeof(ent));
- ret = 0;
- while (likely(i < nr)) {
- ret = aio_read_evt(ctx, &ent);
- if (unlikely(ret <= 0))
- break;
-
- pr_debug("%Lx %Lx %Lx %Lx\n",
- ent.data, ent.obj, ent.res, ent.res2);
-
- /* Could we split the check in two? */
- ret = -EFAULT;
- if (unlikely(copy_to_user(event, &ent, sizeof(ent)))) {
- pr_debug("lost an event due to EFAULT.\n");
- break;
- }
- ret = 0;
-
- /* Good, event copied to userland, update counts. */
- event ++;
- i ++;
- }
-
- if (min_nr <= i)
- return i;
- if (ret)
- return ret;
-
- /* End fast path */
+ ktime_t until = { .tv64 = KTIME_MAX };
+ long ret = 0;

- init_timeout(&to);
if (timeout) {
struct timespec ts;
- ret = -EFAULT;
+
if (unlikely(copy_from_user(&ts, timeout, sizeof(ts))))
- goto out;
+ return -EFAULT;

- set_timeout(start_jiffies, &to, &ts);
+ until = timespec_to_ktime(ts);
}

- while (likely(i < nr)) {
- add_wait_queue_exclusive(&ctx->wait, &wait);
- do {
- set_task_state(tsk, TASK_INTERRUPTIBLE);
- ret = aio_read_evt(ctx, &ent);
- if (ret)
- break;
- if (min_nr <= i)
- break;
- if (unlikely(atomic_read(&ctx->dead))) {
- ret = -EINVAL;
- break;
- }
- if (to.timed_out) /* Only check after read evt */
- break;
- /* Try to only show up in io wait if there are ops
- * in flight */
- if (atomic_read(&ctx->reqs_active))
- io_schedule();
- else
- schedule();
- if (signal_pending(tsk)) {
- ret = -EINTR;
- break;
- }
- /*ret = aio_read_evt(ctx, &ent);*/
- } while (1) ;
-
- set_task_state(tsk, TASK_RUNNING);
- remove_wait_queue(&ctx->wait, &wait);
-
- if (unlikely(ret <= 0))
- break;
-
- ret = -EFAULT;
- if (unlikely(copy_to_user(event, &ent, sizeof(ent)))) {
- pr_debug("lost an event due to EFAULT.\n");
- break;
- }
+ wait_event_interruptible_hrtimeout(ctx->wait,
+ aio_read_events(ctx, min_nr, nr, event, &ret), until);

- /* Good, event copied to userland, update counts. */
- event ++;
- i ++;
- }
+ if (!ret && signal_pending(current))
+ ret = -EINTR;

- if (timeout)
- clear_timeout(&to);
-out:
- destroy_timer_on_stack(&to.timer);
- return i ? i : ret;
+ return ret;
}

/* sys_io_setup:
--
1.7.12


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