reduce l_icloglock roundtrips

All but one caller of xlog_state_want_sync drop and re-acquire
l_icloglock around the call to it, just so that xlog_state_want_sync can
acquire and drop it.

Move all lock operation out of l_icloglock and assert that the lock is
held when it is called.

Note that it would make sense to extende this scheme to
xlog_state_release_iclog, but the locking in there is more complicated
and we'd like to keep the atomic_dec_and_lock optmization for those
callers not having l_icloglock yet.

Signed-off-by: Christoph Hellwig <hch@lst.de>
Reviewed-by: Dave Chinner <david@fromorbit.com>
Signed-off-by: Niv Sardi <xaiki@sgi.com>

1 files changed, 6 insertions, 7 deletions

diff --git a/fs/xfs/xfs_log.c b/fs/xfs/xfs_log.c
index aadaa1472f69..f4726f702a9e 100644
--- a/fs/xfs/xfs_log.c
+++ b/fs/xfs/xfs_log.c
@@ -729,8 +729,8 @@ xfs_log_unmount_write(xfs_mount_t *mp)
                 spin_lock(&log->l_icloglock);
                 iclog = log->l_iclog;
                 atomic_inc(&iclog->ic_refcnt);
-                spin_unlock(&log->l_icloglock);
                 xlog_state_want_sync(log, iclog);
+                spin_unlock(&log->l_icloglock);
                 error = xlog_state_release_iclog(log, iclog);
 
                 spin_lock(&log->l_icloglock);
@@ -767,9 +767,9 @@ xfs_log_unmount_write(xfs_mount_t *mp)
                 spin_lock(&log->l_icloglock);
                 iclog = log->l_iclog;
                 atomic_inc(&iclog->ic_refcnt);
-                spin_unlock(&log->l_icloglock);
 
                 xlog_state_want_sync(log, iclog);
+                spin_unlock(&log->l_icloglock);
                 error =  xlog_state_release_iclog(log, iclog);
 
                 spin_lock(&log->l_icloglock);
@@ -1984,7 +1984,9 @@ xlog_write(xfs_mount_t *	mp,
                 if (iclog->ic_size - log_offset <= sizeof(xlog_op_header_t)) {
                     xlog_state_finish_copy(log, iclog, record_cnt, data_cnt);
                     record_cnt = data_cnt = 0;
+                    spin_lock(&log->l_icloglock);
                     xlog_state_want_sync(log, iclog);
+                    spin_unlock(&log->l_icloglock);
                     if (commit_iclog) {
                         ASSERT(flags & XLOG_COMMIT_TRANS);
                         *commit_iclog = iclog;
@@ -3193,7 +3195,7 @@ try_again:
 STATIC void
 xlog_state_want_sync(xlog_t *log, xlog_in_core_t *iclog)
 {
-        spin_lock(&log->l_icloglock);
+        ASSERT(spin_is_locked(&log->l_icloglock));
 
         if (iclog->ic_state == XLOG_STATE_ACTIVE) {
                 xlog_state_switch_iclogs(log, iclog, 0);
@@ -3201,10 +3203,7 @@ xlog_state_want_sync(xlog_t *log, xlog_in_core_t *iclog)
                 ASSERT(iclog->ic_state &
                         (XLOG_STATE_WANT_SYNC|XLOG_STATE_IOERROR));
         }
-
-        spin_unlock(&log->l_icloglock);
-}       /* xlog_state_want_sync */
-
+}
 
 
 /*****************************************************************************