[PATCH v2 08/10] SUNRPC: serialize iostats updates

Chuck Lever
2014-11-09T01:15:11Z

Occasionally mountstats reports a negative retransmission rate.
Ensure that two RPCs completing concurrently don't confuse the sums
in the transport's op_metrics array.

Since pNFS filelayout can invoke rpc_count_iostats() on another
transport from xprt_release(), we can't rely on simply holding the
transport_lock in xprt_release(). There's nothing for it but hard
serialization. One spin lock per RPC operation should make this as
painless as it can be.

Signed-off-by: Chuck Lever <chuck.lever@oracle.com>
---
include/linux/sunrpc/metrics.h | 3 +++
net/sunrpc/stats.c | 21 ++++++++++++++++-----
2 files changed, 19 insertions(+), 5 deletions(-)

diff --git a/include/linux/sunrpc/metrics.h b/include/linux/sunrpc/metrics.h
index 1565bbe..eecb5a7 100644
--- a/include/linux/sunrpc/metrics.h
+++ b/include/linux/sunrpc/metrics.h
@@ -27,10 +27,13 @@

#include <linux/seq_file.h>
#include <linux/ktime.h>
+#include <linux/spinlock.h>

#define RPC_IOSTATS_VERS "1.0"

struct rpc_iostats {
+ spinlock_t om_lock;
+
/*
* These counters give an idea about how many request
* transmissions are required, on average, to complete that
diff --git a/net/sunrpc/stats.c b/net/sunrpc/stats.c
index 5453049..9711a15 100644
--- a/net/sunrpc/stats.c
+++ b/net/sunrpc/stats.c
@@ -116,7 +116,15 @@ EXPORT_SYMBOL_GPL(svc_seq_show);
*/
struct rpc_iostats *rpc_alloc_iostats(struct rpc_clnt *clnt)
{
- return kcalloc(clnt->cl_maxproc, sizeof(struct rpc_iostats), GFP_KERNEL);
+ struct rpc_iostats *stats;
+ int i;
+
+ stats = kcalloc(clnt->cl_maxproc, sizeof(*stats), GFP_KERNEL);
+ if (stats) {
+ for (i = 0; i < clnt->cl_maxproc; i++)
+ spin_lock_init(&stats[i].om_lock);
+ }
+ return stats;
}
EXPORT_SYMBOL_GPL(rpc_alloc_iostats);

@@ -135,20 +143,21 @@ EXPORT_SYMBOL_GPL(rpc_free_iostats);
* rpc_count_iostats - tally up per-task stats
* @task: completed rpc_task
* @stats: array of stat structures
- *
- * Relies on the caller for serialization.
*/
void rpc_count_iostats(const struct rpc_task *task, struct rpc_iostats *stats)
{
struct rpc_rqst *req = task->tk_rqstp;
struct rpc_iostats *op_metrics;
- ktime_t delta;
+ ktime_t delta, now;

if (!stats || !req)
return;

+ now = ktime_get();
op_metrics = &stats[task->tk_msg.rpc_proc->p_statidx];

+ spin_lock(&op_metrics->om_lock);
+
op_metrics->om_ops++;
op_metrics->om_ntrans += req->rq_ntrans;
op_metrics->om_timeouts += task->tk_timeouts;
@@ -161,8 +170,10 @@ void rpc_count_iostats(const struct rpc_task *task, struct rpc_iostats *stats)

op_metrics->om_rtt = ktime_add(op_metrics->om_rtt, req->rq_rtt);

- delta = ktime_sub(ktime_get(), task->tk_start);
+ delta = ktime_sub(now, task->tk_start);
op_metrics->om_execute = ktime_add(op_metrics->om_execute, delta);
+
+ spin_unlock(&op_metrics->om_lock);
}
EXPORT_SYMBOL_GPL(rpc_count_iostats);