[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>

1 files changed, 26 insertions, 7 deletions

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