[XFS] Per iclog callback chain lock

Rather than use the icloglock for protecting the iclog completion callback
chain, use a new per-iclog lock so that walking the callback chain doesn't
require holding a global lock.

This reduces contention on the icloglock during transaction commit and log
I/O completion by reducing the number of times we need to hold the global
icloglock during these operations.

SGI-PV: 978729
SGI-Modid: xfs-linux-melb:xfs-kern:30770a

Signed-off-by: David Chinner <dgc@sgi.com>
Signed-off-by: Christoph Hellwig <hch@infradead.org>
Signed-off-by: Lachlan McIlroy <lachlan@sgi.com>

2 files changed, 45 insertions, 23 deletions

diff --git a/fs/xfs/xfs_log.c b/fs/xfs/xfs_log.c
index 1fa980933895..7a5b12d93537 100644
--- a/fs/xfs/xfs_log.c
+++ b/fs/xfs/xfs_log.c
@@ -397,12 +397,10 @@ xfs_log_notify(xfs_mount_t	  *mp,		/* mount of partition */
                void               *iclog_hndl,  /* iclog to hang callback off */
                xfs_log_callback_t *cb)
 {
-        xlog_t *log = mp->m_log;
         xlog_in_core_t    *iclog = (xlog_in_core_t *)iclog_hndl;
         int     abortflg;
 
-        cb->cb_next = NULL;
-        spin_lock(&log->l_icloglock);
+        spin_lock(&iclog->ic_callback_lock);
         abortflg = (iclog->ic_state & XLOG_STATE_IOERROR);
         if (!abortflg) {
                 ASSERT_ALWAYS((iclog->ic_state == XLOG_STATE_ACTIVE) ||
@@ -411,7 +409,7 @@ xfs_log_notify(xfs_mount_t	  *mp,		/* mount of partition */
                 *(iclog->ic_callback_tail) = cb;
                 iclog->ic_callback_tail = &(cb->cb_next);
         }
-        spin_unlock(&log->l_icloglock);
+        spin_unlock(&iclog->ic_callback_lock);
         return abortflg;
 }       /* xfs_log_notify */
 
@@ -1257,6 +1255,8 @@ xlog_alloc_log(xfs_mount_t	*mp,
                 iclog->ic_size = XFS_BUF_SIZE(bp) - log->l_iclog_hsize;
                 iclog->ic_state = XLOG_STATE_ACTIVE;
                 iclog->ic_log = log;
+                atomic_set(&iclog->ic_refcnt, 0);
+                spin_lock_init(&iclog->ic_callback_lock);
                 iclog->ic_callback_tail = &(iclog->ic_callback);
                 iclog->ic_datap = (char *)iclog->hic_data + log->l_iclog_hsize;
 
@@ -1987,7 +1987,7 @@ xlog_state_clean_log(xlog_t *log)
                 if (iclog->ic_state == XLOG_STATE_DIRTY) {
                         iclog->ic_state = XLOG_STATE_ACTIVE;
                         iclog->ic_offset       = 0;
-                        iclog->ic_callback      = NULL;   /* don't need to free */
+                        ASSERT(iclog->ic_callback == NULL);
                         /*
                          * If the number of ops in this iclog indicate it just
                          * contains the dummy transaction, we can
@@ -2190,37 +2190,40 @@ xlog_state_do_callback(
                                         be64_to_cpu(iclog->ic_header.h_lsn);
                                 spin_unlock(&log->l_grant_lock);
 
-                                /*
-                                 * Keep processing entries in the callback list
-                                 * until we come around and it is empty.  We
-                                 * need to atomically see that the list is
-                                 * empty and change the state to DIRTY so that
-                                 * we don't miss any more callbacks being added.
-                                 */
-                                spin_lock(&log->l_icloglock);
                         } else {
+                                spin_unlock(&log->l_icloglock);
                                 ioerrors++;
                         }
-                        cb = iclog->ic_callback;
 
+                        /*
+                         * Keep processing entries in the callback list until
+                         * we come around and it is empty.  We need to
+                         * atomically see that the list is empty and change the
+                         * state to DIRTY so that we don't miss any more
+                         * callbacks being added.
+                         */
+                        spin_lock(&iclog->ic_callback_lock);
+                        cb = iclog->ic_callback;
                         while (cb) {
                                 iclog->ic_callback_tail = &(iclog->ic_callback);
                                 iclog->ic_callback = NULL;
-                                spin_unlock(&log->l_icloglock);
+                                spin_unlock(&iclog->ic_callback_lock);
 
                                 /* perform callbacks in the order given */
                                 for (; cb; cb = cb_next) {
                                         cb_next = cb->cb_next;
                                         cb->cb_func(cb->cb_arg, aborted);
                                 }
-                                spin_lock(&log->l_icloglock);
+                                spin_lock(&iclog->ic_callback_lock);
                                 cb = iclog->ic_callback;
                         }
 
                         loopdidcallbacks++;
                         funcdidcallbacks++;
 
+                        spin_lock(&log->l_icloglock);
                         ASSERT(iclog->ic_callback == NULL);
+                        spin_unlock(&iclog->ic_callback_lock);
                         if (!(iclog->ic_state & XLOG_STATE_IOERROR))
                                 iclog->ic_state = XLOG_STATE_DIRTY;
 
diff --git a/fs/xfs/xfs_log_priv.h b/fs/xfs/xfs_log_priv.h
index 01c63db25a1d..104b623aa082 100644
--- a/fs/xfs/xfs_log_priv.h
+++ b/fs/xfs/xfs_log_priv.h
@@ -324,6 +324,19 @@ typedef struct xlog_rec_ext_header {
  * - ic_offset is the current number of bytes written to in this iclog.
  * - ic_refcnt is bumped when someone is writing to the log.
  * - ic_state is the state of the iclog.
+ *
+ * Because of cacheline contention on large machines, we need to separate
+ * various resources onto different cachelines. To start with, make the
+ * structure cacheline aligned. The following fields can be contended on
+ * by independent processes:
+ *
+ *      - ic_callback_*
+ *      - ic_refcnt
+ *      - fields protected by the global l_icloglock
+ *
+ * so we need to ensure that these fields are located in separate cachelines.
+ * We'll put all the read-only and l_icloglock fields in the first cacheline,
+ * and move everything else out to subsequent cachelines.
  */
 typedef struct xlog_iclog_fields {
         sv_t                    ic_forcesema;
@@ -332,18 +345,23 @@ typedef struct xlog_iclog_fields {
         struct xlog_in_core     *ic_prev;
         struct xfs_buf          *ic_bp;
         struct log              *ic_log;
-        xfs_log_callback_t      *ic_callback;
-        xfs_log_callback_t      **ic_callback_tail;
-#ifdef XFS_LOG_TRACE
-        struct ktrace           *ic_trace;
-#endif
         int                     ic_size;
         int                     ic_offset;
-        atomic_t                ic_refcnt;
         int                     ic_bwritecnt;
         ushort_t                ic_state;
         char                    *ic_datap;      /* pointer to iclog data */
-} xlog_iclog_fields_t;
+#ifdef XFS_LOG_TRACE
+        struct ktrace           *ic_trace;
+#endif
+
+        /* Callback structures need their own cacheline */
+        spinlock_t              ic_callback_lock ____cacheline_aligned_in_smp;
+        xfs_log_callback_t      *ic_callback;
+        xfs_log_callback_t      **ic_callback_tail;
+
+        /* reference counts need their own cacheline */
+        atomic_t                ic_refcnt ____cacheline_aligned_in_smp;
+} xlog_iclog_fields_t ____cacheline_aligned_in_smp;
 
 typedef union xlog_in_core2 {
         xlog_rec_header_t       hic_header;
@@ -366,6 +384,7 @@ typedef struct xlog_in_core {
 #define ic_bp           hic_fields.ic_bp
 #define ic_log          hic_fields.ic_log
 #define ic_callback     hic_fields.ic_callback
+#define ic_callback_lock hic_fields.ic_callback_lock
 #define ic_callback_tail hic_fields.ic_callback_tail
 #define ic_trace        hic_fields.ic_trace
 #define ic_size         hic_fields.ic_size