In the current log space reservation slowpath code, the log space
waiters are waken up by an incoming waiter while holding the lock. As
the process of waking up a task can be time consuming, doing it while
holding the lock can make spinlock contention, if present, more severe.
This patch changes the slowpath code to use the wake_q for waking up
tasks without holding the lock, thus improving performance and reducing
spinlock contention level.
Running the AIM7 fserver workload on a 2-socket 24-core 48-thread
Broadwell system with a small xfs filesystem on ramfs, the performance
increased from 192,666 jobs/min to 285,221 with this change.
Signed-off-by: Waiman Long <longman@xxxxxxxxxx>
---
fs/xfs/xfs_linux.h | 1 +
fs/xfs/xfs_log.c | 50 ++++++++++++++++++++++++++++++++++++----------
2 files changed, 41 insertions(+), 10 deletions(-)
diff --git a/fs/xfs/xfs_linux.h b/fs/xfs/xfs_linux.h
index edbd5a210df2..1548a353da1e 100644
--- a/fs/xfs/xfs_linux.h
+++ b/fs/xfs/xfs_linux.h
@@ -60,6 +60,7 @@ typedef __u32 xfs_nlink_t;
#include <linux/list_sort.h>
#include <linux/ratelimit.h>
#include <linux/rhashtable.h>
+#include <linux/sched/wake_q.h>
#include <asm/page.h>
#include <asm/div64.h>
diff --git a/fs/xfs/xfs_log.c b/fs/xfs/xfs_log.c
index ac1dc8db7112..70d5f85ff059 100644
--- a/fs/xfs/xfs_log.c
+++ b/fs/xfs/xfs_log.c
@@ -221,7 +221,8 @@ STATIC bool
xlog_grant_head_wake(
struct xlog *log,
struct xlog_grant_head *head,
- int *free_bytes)
+ int *free_bytes,
+ struct wake_q_head *wakeq)
{
struct xlog_ticket *tic;
int need_bytes;
@@ -240,7 +241,7 @@ xlog_grant_head_wake(
continue;
trace_xfs_log_grant_wake_up(log, tic);
- wake_up_process(tic->t_task);
+ wake_q_add(wakeq, tic->t_task);
tic->t_flags |= XLOG_TIC_WAKING;
}
@@ -252,8 +253,9 @@ xlog_grant_head_wait(
struct xlog *log,
struct xlog_grant_head *head,
struct xlog_ticket *tic,
- int need_bytes) __releases(&head->lock)
- __acquires(&head->lock)
+ int need_bytes,
+ struct wake_q_head *wakeq) __releases(&head->lock)
+ __acquires(&head->lock)
{
list_add_tail(&tic->t_queue, &head->waiters);
@@ -265,6 +267,11 @@ xlog_grant_head_wait(
__set_current_state(TASK_UNINTERRUPTIBLE);
spin_unlock(&head->lock);
+ if (wakeq) {
+ wake_up_q(wakeq);
+ wakeq = NULL;
+ }
+
XFS_STATS_INC(log->l_mp, xs_sleep_logspace);
trace_xfs_log_grant_sleep(log, tic);
@@ -272,7 +279,21 @@ xlog_grant_head_wait(
trace_xfs_log_grant_wake(log, tic);
spin_lock(&head->lock);
- tic->t_flags &= ~XLOG_TIC_WAKING;
+ /*
+ * The XLOG_TIC_WAKING flag should be set. However, it is
+ * very unlikely that the current task is still in the
+ * wake_q. If that happens (maybe anonymous wakeup), we
+ * have to wait until the task is dequeued before proceeding
+ * to avoid the possibility of having the task put into
+ * another wake_q simultaneously.
+ */
+ if (tic->t_flags & XLOG_TIC_WAKING) {
+ while (task_in_wake_q(current))
+ cpu_relax();
+
+ tic->t_flags &= ~XLOG_TIC_WAKING;
+ }
+
if (XLOG_FORCED_SHUTDOWN(log))
goto shutdown;
} while (xlog_space_left(log, &head->grant) < need_bytes);
@@ -310,6 +331,7 @@ xlog_grant_head_check(
{
int free_bytes;
int error = 0;
+ DEFINE_WAKE_Q(wakeq);
ASSERT(!(log->l_flags & XLOG_ACTIVE_RECOVERY));
@@ -323,15 +345,17 @@ xlog_grant_head_check(
free_bytes = xlog_space_left(log, &head->grant);
if (!list_empty_careful(&head->waiters)) {
spin_lock(&head->lock);
- if (!xlog_grant_head_wake(log, head, &free_bytes) ||
+ if (!xlog_grant_head_wake(log, head, &free_bytes, &wakeq) ||
free_bytes < *need_bytes) {
error = xlog_grant_head_wait(log, head, tic,
- *need_bytes);
+ *need_bytes, &wakeq);
+ wake_q_init(&wakeq); /* Set wake_q to empty */
}
spin_unlock(&head->lock);
+ wake_up_q(&wakeq);
} else if (free_bytes < *need_bytes) {
spin_lock(&head->lock);
- error = xlog_grant_head_wait(log, head, tic, *need_bytes);
+ error = xlog_grant_head_wait(log, head, tic, *need_bytes, NULL);
spin_unlock(&head->lock);
}
@@ -1077,6 +1101,7 @@ xfs_log_space_wake(
{
struct xlog *log = mp->m_log;
int free_bytes;
+ DEFINE_WAKE_Q(wakeq);
if (XLOG_FORCED_SHUTDOWN(log))
return;
@@ -1086,8 +1111,11 @@ xfs_log_space_wake(
spin_lock(&log->l_write_head.lock);
free_bytes = xlog_space_left(log, &log->l_write_head.grant);
- xlog_grant_head_wake(log, &log->l_write_head, &free_bytes);
+ xlog_grant_head_wake(log, &log->l_write_head, &free_bytes,
+ &wakeq);
spin_unlock(&log->l_write_head.lock);
+ wake_up_q(&wakeq);
+ wake_q_init(&wakeq); /* Re-init wake_q to be reused again */
}
if (!list_empty_careful(&log->l_reserve_head.waiters)) {
@@ -1095,8 +1123,10 @@ xfs_log_space_wake(
spin_lock(&log->l_reserve_head.lock);
free_bytes = xlog_space_left(log, &log->l_reserve_head.grant);
- xlog_grant_head_wake(log, &log->l_reserve_head, &free_bytes);
+ xlog_grant_head_wake(log, &log->l_reserve_head, &free_bytes,
+ &wakeq);
spin_unlock(&log->l_reserve_head.lock);
+ wake_up_q(&wakeq);
}
}
--
2.18.0
