Hi Trond-
On Apr 19, 2008, at 4:40 PM, Trond Myklebust wrote:
The rest of the networking layer uses SOCK_ASYNC_NOSPACE to signal
whether
or not we have someone waiting for buffer memory. Convert the SUNRPC
layer
to use the same idiom.
As near as I can tell, SOCK_NOSPACE is used for this purpose. It
really isn't clear what SOCK_ASYNC_NOSPACE is used for.
In fact I found at least one comment that suggested these flags
currently may be used inconsistently in the network layer. Did you
happen to find any unambiguous documentation explaining how the
network layer uses these flags? (I for one would like to understand
this better).
I'm a little concerned about this patch overall because the
SOCK_NOSPACE flags interface is well understood by only a handful of
people in the universe, so it's difficult for us networking outsiders
to evaluate this patch.
Remove the unlikely()s in xs_udp_write_space and xs_tcp_write_space.
In
fact, the most common case will be that there is nobody waiting for
buffer
space.
The original purpose of the unlikely() here was to prevent the
compiler from reordering the out: arm and xprt_write_space, thus
generating unnecessarily complex object code. I may even have tested
this with oprofile on Pentium III.
Not sure it makes any difference at all these days... but you could
move this change to a separate clean up patch, for clarity.
SOCK_NOSPACE is there to tell the TCP layer whether or not the cwnd
was
limited by the application window. Ensure that we follow the same
idiom as
the rest of the networking layer here too.
My cursory review of the network layer suggests that this usage of
SOCK_NOSPACE is an expediency, not the main purpose of SOCK_NOSPACE.
This could be a useful change though... it would be nice to have a
clear explanation in the patch description of the actual benefit this
brings to the RPC's TCP socket transport.
Finally, ensure that we clear SOCK_ASYNC_NOSPACE once we wake up, so
that
write_space() doesn't keep waking things up on xprt->pending.
This is probably the main fix introduced by this patch. Is there a
measureable performance gain?
You also moved the transport lock around in xs_nospace (maybe to
additionally protect the xprt connection flags?), and introduced the
use of sk_write_pending in the RPC socket transport, but those changes
are not documented in the patch description. Was the transport lock
change a bug fix, or a necessity of the other changes you're making in
this patch?
Lastly, if there is a palpable benefit to these changes, it would be
great if the server side write space support could be updated as well.
Signed-off-by: Trond Myklebust <Trond.Myklebust@xxxxxxxxxx>
---
include/linux/sunrpc/xprt.h | 2 +
net/sunrpc/xprt.c | 4 +--
net/sunrpc/xprtsock.c | 61 ++++++++++++++++++++++++++++
+--------------
3 files changed, 44 insertions(+), 23 deletions(-)
diff --git a/include/linux/sunrpc/xprt.h b/include/linux/sunrpc/xprt.h
index b3ff9a8..8a0629a 100644
--- a/include/linux/sunrpc/xprt.h
+++ b/include/linux/sunrpc/xprt.h
@@ -232,7 +232,7 @@ int xprt_unregister_transport(struct
xprt_class *type);
void xprt_set_retrans_timeout_def(struct rpc_task *task);
void xprt_set_retrans_timeout_rtt(struct rpc_task *task);
void xprt_wake_pending_tasks(struct rpc_xprt *xprt, int status);
-void xprt_wait_for_buffer_space(struct rpc_task *task);
+void xprt_wait_for_buffer_space(struct rpc_task *task, rpc_action
action);
void xprt_write_space(struct rpc_xprt *xprt);
void xprt_update_rtt(struct rpc_task *task);
void xprt_adjust_cwnd(struct rpc_task *task, int result);
diff --git a/net/sunrpc/xprt.c b/net/sunrpc/xprt.c
index 85199c6..3ba64f9 100644
--- a/net/sunrpc/xprt.c
+++ b/net/sunrpc/xprt.c
@@ -447,13 +447,13 @@ EXPORT_SYMBOL_GPL(xprt_wake_pending_tasks);
* @task: task to be put to sleep
+ * @action: function to call on wake up
*
*/
-void xprt_wait_for_buffer_space(struct rpc_task *task)
+void xprt_wait_for_buffer_space(struct rpc_task *task, rpc_action
action)
{
struct rpc_rqst *req = task->tk_rqstp;
struct rpc_xprt *xprt = req->rq_xprt;
task->tk_timeout = req->rq_timeout;
- rpc_sleep_on(&xprt->pending, task, NULL);
+ rpc_sleep_on(&xprt->pending, task, action);
}
EXPORT_SYMBOL_GPL(xprt_wait_for_buffer_space);
diff --git a/net/sunrpc/xprtsock.c b/net/sunrpc/xprtsock.c
index 8bd3b0f..4c2462e 100644
--- a/net/sunrpc/xprtsock.c
+++ b/net/sunrpc/xprtsock.c
@@ -516,6 +516,14 @@ out:
return sent;
}
+static void xs_nospace_callback(struct rpc_task *task)
+{
+ struct sock_xprt *transport = container_of(task->tk_rqstp-
>rq_xprt, struct sock_xprt, xprt);
+
+ transport->inet->sk_write_pending--;
+ clear_bit(SOCK_ASYNC_NOSPACE, &transport->sock->flags);
+}
+
/**
* xs_nospace - place task on wait queue if transmit was incomplete
* @task: task to put to sleep
@@ -531,20 +539,27 @@ static void xs_nospace(struct rpc_task *task)
task->tk_pid, req->rq_slen - req->rq_bytes_sent,
req->rq_slen);
- if (test_bit(SOCK_ASYNC_NOSPACE, &transport->sock->flags)) {
- /* Protect against races with write_space */
- spin_lock_bh(&xprt->transport_lock);
-
- /* Don't race with disconnect */
- if (!xprt_connected(xprt))
- task->tk_status = -ENOTCONN;
- else if (test_bit(SOCK_NOSPACE, &transport->sock->flags))
- xprt_wait_for_buffer_space(task);
+ /* Protect against races with write_space */
+ spin_lock_bh(&xprt->transport_lock);
+
+ /* Don't race with disconnect */
+ if (xprt_connected(xprt)) {
+ if (test_bit(SOCK_ASYNC_NOSPACE, &transport->sock->flags)) {
+ /*
+ * Notify TCP that we're limited by the application
+ * window size
+ */
+ set_bit(SOCK_NOSPACE, &transport->sock->flags);
+ transport->inet->sk_write_pending++;
+ /* ...and wait for more buffer space */
+ xprt_wait_for_buffer_space(task, xs_nospace_callback);
+ }
+ } else {
+ clear_bit(SOCK_ASYNC_NOSPACE, &transport->sock->flags);
+ task->tk_status = -ENOTCONN;
+ }
- spin_unlock_bh(&xprt->transport_lock);
- } else
- /* Keep holding the socket if it is blocked */
- rpc_delay(task, HZ>>4);
+ spin_unlock_bh(&xprt->transport_lock);
}
/**
@@ -588,19 +603,20 @@ static int xs_udp_send_request(struct rpc_task
*task)
}
switch (status) {
+ case -EAGAIN:
+ xs_nospace(task);
+ break;
case -ENETUNREACH:
case -EPIPE:
case -ECONNREFUSED:
/* When the server has died, an ICMP port unreachable message
* prompts ECONNREFUSED. */
- break;
- case -EAGAIN:
- xs_nospace(task);
+ clear_bit(SOCK_ASYNC_NOSPACE, &transport->sock->flags);
break;
default:
+ clear_bit(SOCK_ASYNC_NOSPACE, &transport->sock->flags);
dprintk("RPC: sendmsg returned unrecognized error %d\n",
-status);
- break;
}
return status;
@@ -695,12 +711,13 @@ static int xs_tcp_send_request(struct rpc_task
*task)
case -ENOTCONN:
case -EPIPE:
status = -ENOTCONN;
+ clear_bit(SOCK_ASYNC_NOSPACE, &transport->sock->flags);
break;
default:
dprintk("RPC: sendmsg returned unrecognized error %d\n",
-status);
+ clear_bit(SOCK_ASYNC_NOSPACE, &transport->sock->flags);
xs_tcp_shutdown(xprt);
- break;
}
return status;
@@ -1189,9 +1206,11 @@ static void xs_udp_write_space(struct sock *sk)
if (unlikely(!(sock = sk->sk_socket)))
goto out;
+ clear_bit(SOCK_NOSPACE, &sock->flags);
+
if (unlikely(!(xprt = xprt_from_sock(sk))))
goto out;
- if (unlikely(!test_and_clear_bit(SOCK_NOSPACE, &sock->flags)))
+ if (test_and_clear_bit(SOCK_ASYNC_NOSPACE, &sock->flags) == 0)
goto out;
xprt_write_space(xprt);
@@ -1222,9 +1241,11 @@ static void xs_tcp_write_space(struct sock *sk)
if (unlikely(!(sock = sk->sk_socket)))
goto out;
+ clear_bit(SOCK_NOSPACE, &sock->flags);
+
if (unlikely(!(xprt = xprt_from_sock(sk))))
goto out;
- if (unlikely(!test_and_clear_bit(SOCK_NOSPACE, &sock->flags)))
+ if (test_and_clear_bit(SOCK_ASYNC_NOSPACE, &sock->flags) == 0)
goto out;
xprt_write_space(xprt);
--
Chuck Lever
chuck[dot]lever[at]oracle[dot]com
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