SUNRPC: Replace jiffies-based metrics with ktime-based metrics

Currently RPC performance metrics that tabulate elapsed time use
jiffies time values.  This is problematic on systems that use slow
jiffies (for instance 100HZ systems built for paravirtualized
environments).  It is also a problem for computing precise latency
statistics for advanced network transports, such as InfiniBand,
that can have round-trip latencies significanly faster than a single
clock tick.

For the RPC client, adopt the high resolution time stamp mechanism
already used by the network layer and blktrace: ktime.

We use ktime format time stamps for all internal computations, and
convert to milliseconds for presentation.  As a result, we need only
addition operations in the performance critical paths; multiply/divide
is required only for presentation.

We could report RTT metrics in microseconds.  In fact the mountstats
format is versioned to accomodate exactly this kind of interface
improvement.

For now, however, we'll stay with millisecond precision for
presentation to maintain backwards compatibility with the handful of
currently deployed user space tools.  At a later point, we'll move to
an API such as BDI_STATS where a finer timestamp precision can be
reported.

Signed-off-by: Chuck Lever <chuck.lever@oracle.com>
Signed-off-by: Trond Myklebust <Trond.Myklebust@netapp.com>

3 files changed, 9 insertions, 6 deletions

diff --git a/include/linux/sunrpc/metrics.h b/include/linux/sunrpc/metrics.h
index 77f78e56c481..b6edbc0ea83d 100644
--- a/include/linux/sunrpc/metrics.h
+++ b/include/linux/sunrpc/metrics.h
@@ -26,6 +26,7 @@
 #define _LINUX_SUNRPC_METRICS_H
 
 #include <linux/seq_file.h>
+#include <linux/ktime.h>
 
 #define RPC_IOSTATS_VERS        "1.0"
 
@@ -58,9 +59,9 @@ struct rpc_iostats {
          * and the total time the request spent from init to release
          * are measured.
          */
-        unsigned long long      om_queue,       /* jiffies queued for xmit */
-                                om_rtt,         /* jiffies for RPC RTT */
-                                om_execute;     /* jiffies for RPC execution */
+        ktime_t                 om_queue,       /* queued for xmit */
+                                om_rtt,         /* RPC RTT */
+                                om_execute;     /* RPC execution */
 } ____cacheline_aligned;
 
 struct rpc_task;
diff --git a/include/linux/sunrpc/sched.h b/include/linux/sunrpc/sched.h
index 7bc7fd5291ce..76720d262ef2 100644
--- a/include/linux/sunrpc/sched.h
+++ b/include/linux/sunrpc/sched.h
@@ -10,6 +10,7 @@
 #define _LINUX_SUNRPC_SCHED_H_
 
 #include <linux/timer.h>
+#include <linux/ktime.h>
 #include <linux/sunrpc/types.h>
 #include <linux/spinlock.h>
 #include <linux/wait.h>
@@ -80,8 +81,8 @@ struct rpc_task {
 
         unsigned short          tk_timeouts;    /* maj timeouts */
         size_t                  tk_bytes_sent;  /* total bytes sent */
-        unsigned long           tk_start;       /* RPC task init timestamp */
-        long                    tk_rtt;         /* round-trip time (jiffies) */
+        ktime_t                 tk_start,       /* RPC task init timestamp */
+                                tk_rtt;         /* round-trip time */
 
         pid_t                   tk_owner;       /* Process id for batching tasks */
         unsigned char           tk_priority : 2;/* Task priority */
diff --git a/include/linux/sunrpc/xprt.h b/include/linux/sunrpc/xprt.h
index 04fc342d9840..f8851861b744 100644
--- a/include/linux/sunrpc/xprt.h
+++ b/include/linux/sunrpc/xprt.h
@@ -13,6 +13,7 @@
 #include <linux/socket.h>
 #include <linux/in.h>
 #include <linux/kref.h>
+#include <linux/ktime.h>
 #include <linux/sunrpc/sched.h>
 #include <linux/sunrpc/xdr.h>
 #include <linux/sunrpc/msg_prot.h>
@@ -94,7 +95,7 @@ struct rpc_rqst {
          */
         u32                     rq_bytes_sent;  /* Bytes we have sent */
 
-        unsigned long           rq_xtime;       /* when transmitted */
+        ktime_t                 rq_xtime;       /* transmit time stamp */
         int                     rq_ntrans;
 
 #if defined(CONFIG_NFS_V4_1)