block: Compute minimum, maximum and average I/O latencies

This patch keeps track of the minimum, maximum and average latencies
of I/O operations during a certain interval of time.

The values are exposed in the BlockDeviceTimedStats structure.

An option to define the intervals to collect these statistics will be
added in a separate patch.

Signed-off-by: Alberto Garcia <berto@igalia.com>
Message-id: c7382dc89622c64f918d09f32815827772628f8e.1446044837.git.berto@igalia.com
Signed-off-by: Stefan Hajnoczi <stefanha@redhat.com>
Signed-off-by: Kevin Wolf <kwolf@redhat.com>

1 files changed, 14 insertions, 0 deletions

diff --git a/include/block/accounting.h b/include/block/accounting.h
index 0d9b076..1dd582a 100644
--- a/include/block/accounting.h
+++ b/include/block/accounting.h
@@ -28,6 +28,9 @@
 #include <stdbool.h>
 
 #include "qemu/typedefs.h"
+#include "qemu/timed-average.h"
+
+typedef struct BlockAcctTimedStats BlockAcctTimedStats;
 
 enum BlockAcctType {
     BLOCK_ACCT_READ,
@@ -36,6 +39,12 @@ enum BlockAcctType {
     BLOCK_MAX_IOTYPE,
 };
 
+struct BlockAcctTimedStats {
+    TimedAverage latency[BLOCK_MAX_IOTYPE];
+    unsigned interval_length; /* in seconds */
+    QSLIST_ENTRY(BlockAcctTimedStats) entries;
+};
+
 typedef struct BlockAcctStats {
     uint64_t nr_bytes[BLOCK_MAX_IOTYPE];
     uint64_t nr_ops[BLOCK_MAX_IOTYPE];
@@ -44,6 +53,7 @@ typedef struct BlockAcctStats {
     uint64_t total_time_ns[BLOCK_MAX_IOTYPE];
     uint64_t merged[BLOCK_MAX_IOTYPE];
     int64_t last_access_time_ns;
+    QSLIST_HEAD(, BlockAcctTimedStats) intervals;
     bool account_invalid;
     bool account_failed;
 } BlockAcctStats;
@@ -56,6 +66,10 @@ typedef struct BlockAcctCookie {
 
 void block_acct_init(BlockAcctStats *stats, bool account_invalid,
                      bool account_failed);
+void block_acct_cleanup(BlockAcctStats *stats);
+void block_acct_add_interval(BlockAcctStats *stats, unsigned interval_length);
+BlockAcctTimedStats *block_acct_interval_next(BlockAcctStats *stats,
+                                              BlockAcctTimedStats *s);
 void block_acct_start(BlockAcctStats *stats, BlockAcctCookie *cookie,
                       int64_t bytes, enum BlockAcctType type);
 void block_acct_done(BlockAcctStats *stats, BlockAcctCookie *cookie);