[XFS] Use atomic counters for ktrace buffer indexes
ktrace_enter() is consuming vast amounts of CPU time due to the use of a
single global lock for protecting buffer index increments. Change it to
use per-buffer atomic counters - this reduces ktrace_enter() overhead
during a trace intensive test on a 4p machine from 58% of all CPU time to
12% and halves test runtime.
SGI-PV: 977546
SGI-Modid: xfs-linux-melb:xfs-kern:30537a
Signed-off-by: David Chinner <dgc@sgi.com>
Signed-off-by: Christoph Hellwig <hch@infradead.org>
Signed-off-by: Lachlan McIlroy <lachlan@sgi.com>
diff --git a/fs/xfs/support/ktrace.h b/fs/xfs/support/ktrace.h
index 56e72b4..782dbbb 100644
--- a/fs/xfs/support/ktrace.h
+++ b/fs/xfs/support/ktrace.h
@@ -30,7 +30,7 @@
*/
typedef struct ktrace {
int kt_nentries; /* number of entries in trace buf */
- int kt_index; /* current index in entries */
+ atomic_t kt_index; /* current index in entries */
int kt_rollover;
ktrace_entry_t *kt_entries; /* buffer of entries */
} ktrace_t;