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

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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>
This commit is contained in:
Chuck Lever 2010-05-07 13:34:47 -04:00 • committed by Trond Myklebust
parent f56916b97f
commit ff8399709e
6 changed files with 24 additions and 28 deletions
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5
include/linux/sunrpc/sched.h
View file

@ -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 */