Commit 0971374e authored by Trond Myklebust's avatar Trond Myklebust Committed by J. Bruce Fields
Browse files

SUNRPC: Reduce contention in svc_xprt_enqueue() 



Ensure that all calls to svc_xprt_enqueue() except svc_xprt_received()
check the value of XPT_BUSY, before attempting to grab spinlocks etc.
This is to avoid situations such as the following "perf" trace,
which shows heavy contention on the pool spinlock:

    54.15%            nfsd  [kernel.kallsyms]        [k] _raw_spin_lock_bh
                      |
                      --- _raw_spin_lock_bh
                         |
                         |--71.43%-- svc_xprt_enqueue
                         |          |
                         |          |--50.31%-- svc_reserve
                         |          |
                         |          |--31.35%-- svc_xprt_received
                         |          |
                         |          |--18.34%-- svc_tcp_data_ready
...

Signed-off-by: default avatarTrond Myklebust <trond.myklebust@primarydata.com>
Signed-off-by: default avatarJ. Bruce Fields <bfields@redhat.com>
parent 650ecc8f

net/sunrpc/svc_xprt.c

+17 −8
Original line number Diff line number Diff line
@@ -23,6 +23,7 @@ static int svc_deferred_recv(struct svc_rqst *rqstp); 
static struct cache_deferred_req *svc_defer(struct cache_req *req);

static void svc_age_temp_xprts(unsigned long closure);

static void svc_delete_xprt(struct svc_xprt *xprt);

static void svc_xprt_do_enqueue(struct svc_xprt *xprt);



/* apparently the "standard" is that clients close

 * idle connections after 5 minutes, servers after
@@ -222,11 +223,12 @@ static void svc_xprt_received(struct svc_xprt *xprt) 
	if (!test_bit(XPT_BUSY, &xprt->xpt_flags))

		return;

	/* As soon as we clear busy, the xprt could be closed and

	 * 'put', so we need a reference to call svc_xprt_enqueue with:

	 * 'put', so we need a reference to call svc_xprt_do_enqueue with:

	 */

	svc_xprt_get(xprt);

	smp_mb__before_atomic();

	clear_bit(XPT_BUSY, &xprt->xpt_flags);

	svc_xprt_enqueue(xprt);

	svc_xprt_do_enqueue(xprt);

	svc_xprt_put(xprt);

}
@@ -335,12 +337,7 @@ static bool svc_xprt_has_something_to_do(struct svc_xprt *xprt) 
	return false;

}



/*

 * Queue up a transport with data pending. If there are idle nfsd

 * processes, wake 'em up.

 *

 */

void svc_xprt_enqueue(struct svc_xprt *xprt)

static void svc_xprt_do_enqueue(struct svc_xprt *xprt)

{

	struct svc_pool *pool;

	struct svc_rqst	*rqstp;
@@ -398,6 +395,18 @@ void svc_xprt_enqueue(struct svc_xprt *xprt) 
out_unlock:

	spin_unlock_bh(&pool->sp_lock);

}



/*

 * Queue up a transport with data pending. If there are idle nfsd

 * processes, wake 'em up.

 *

 */

void svc_xprt_enqueue(struct svc_xprt *xprt)

{

	if (test_bit(XPT_BUSY, &xprt->xpt_flags))

		return;

	svc_xprt_do_enqueue(xprt);

}

EXPORT_SYMBOL_GPL(svc_xprt_enqueue);



/*

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