From: "J. Bruce Fields" <bfields@fieldses.org>
To: Michael Tokarev <mjt@tls.msk.ru>
Cc: "Myklebust, Trond" <Trond.Myklebust@netapp.com>,
"linux-nfs@vger.kernel.org" <linux-nfs@vger.kernel.org>,
Linux-kernel <linux-kernel@vger.kernel.org>,
Eric Dumazet <eric.dumazet@gmail.com>
Subject: Re: 3.0+ NFS issues (bisected)
Date: Fri, 17 Aug 2012 18:32:53 -0400 [thread overview]
Message-ID: <20120817223253.GA15659@fieldses.org> (raw)
In-Reply-To: <20120817200807.GB14620@fieldses.org>
On Fri, Aug 17, 2012 at 04:08:07PM -0400, J. Bruce Fields wrote:
> Wait a minute, that assumption's a problem because that calculation
> depends in part on xpt_reserved, which is changed here....
>
> In particular, svc_xprt_release() calls svc_reserve(rqstp, 0), which
> subtracts rqstp->rq_reserved and then calls svc_xprt_enqueue, now with a
> lower xpt_reserved value. That could well explain this.
So, maybe something like this?
--b.
commit c8136c319ad85d0db870021fc3f9074d37f26d4a
Author: J. Bruce Fields <bfields@redhat.com>
Date: Fri Aug 17 17:31:53 2012 -0400
svcrpc: don't add to xpt_reserved till we receive
The rpc server tries to ensure that there will be room to send a reply
before it receives a request.
It does this by tracking, in xpt_reserved, an upper bound on the total
size of the replies that is has already committed to for the socket.
Currently it is adding in the estimate for a new reply *before* it
checks whether there is space available. If it finds that there is not
space, it then subtracts the estimate back out.
This may lead the subsequent svc_xprt_enqueue to decide that there is
space after all.
The results is a svc_recv() that will repeatedly return -EAGAIN, causing
server threads to loop without doing any actual work.
Reported-by: Michael Tokarev <mjt@tls.msk.ru>
Signed-off-by: J. Bruce Fields <bfields@redhat.com>
diff --git a/net/sunrpc/svc_xprt.c b/net/sunrpc/svc_xprt.c
index ec99849a..59ff3a3 100644
--- a/net/sunrpc/svc_xprt.c
+++ b/net/sunrpc/svc_xprt.c
@@ -366,8 +366,6 @@ void svc_xprt_enqueue(struct svc_xprt *xprt)
rqstp, rqstp->rq_xprt);
rqstp->rq_xprt = xprt;
svc_xprt_get(xprt);
- rqstp->rq_reserved = serv->sv_max_mesg;
- atomic_add(rqstp->rq_reserved, &xprt->xpt_reserved);
pool->sp_stats.threads_woken++;
wake_up(&rqstp->rq_wait);
} else {
@@ -644,8 +642,6 @@ int svc_recv(struct svc_rqst *rqstp, long timeout)
if (xprt) {
rqstp->rq_xprt = xprt;
svc_xprt_get(xprt);
- rqstp->rq_reserved = serv->sv_max_mesg;
- atomic_add(rqstp->rq_reserved, &xprt->xpt_reserved);
/* As there is a shortage of threads and this request
* had to be queued, don't allow the thread to wait so
@@ -743,6 +739,10 @@ int svc_recv(struct svc_rqst *rqstp, long timeout)
len = xprt->xpt_ops->xpo_recvfrom(rqstp);
dprintk("svc: got len=%d\n", len);
}
+ if (len > 0) {
+ rqstp->rq_reserved = serv->sv_max_mesg;
+ atomic_add(rqstp->rq_reserved, &xprt->xpt_reserved);
+ }
svc_xprt_received(xprt);
/* No data, incomplete (TCP) read, or accept() */
next prev parent reply other threads:[~2012-08-17 22:33 UTC|newest]
Thread overview: 24+ messages / expand[flat|nested] mbox.gz Atom feed top
2012-05-25 6:53 3.0+ NFS issues Michael Tokarev
2012-05-29 15:24 ` J. Bruce Fields
2012-05-30 7:11 ` Michael Tokarev
2012-05-30 13:25 ` J. Bruce Fields
2012-05-31 6:47 ` Michael Tokarev
2012-05-31 12:59 ` Myklebust, Trond
2012-05-31 13:24 ` Michael Tokarev
2012-05-31 13:46 ` Myklebust, Trond
2012-05-31 13:51 ` Michael Tokarev
2012-07-10 12:52 ` Michael Tokarev
2012-07-12 12:53 ` J. Bruce Fields
2012-08-17 1:56 ` 3.0+ NFS issues (bisected) Michael Tokarev
2012-08-17 14:56 ` J. Bruce Fields
2012-08-17 16:00 ` J. Bruce Fields
2012-08-17 17:12 ` Michael Tokarev
2012-08-17 17:18 ` J. Bruce Fields
2012-08-17 17:26 ` Michael Tokarev
2012-08-17 17:29 ` Michael Tokarev
2012-08-17 19:18 ` J. Bruce Fields
2012-08-17 20:08 ` J. Bruce Fields
2012-08-17 22:32 ` J. Bruce Fields [this message]
2012-08-18 6:49 ` Michael Tokarev
2012-08-18 11:13 ` J. Bruce Fields
2012-08-18 12:58 ` Michael Tokarev
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