linux-kernel - Re: High load in 2.6.27, NFS / rpcauth_lookup

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Date:	Wed, 19 Nov 2008 17:31:01 -0500
From:	Trond Myklebust <trond.myklebust@....uio.no>
To:	Max Kellermann <max@...mpel.org>
Cc:	linux-kernel@...r.kernel.org, linux-nfs@...r.kernel.org
Subject: Re: High load in 2.6.27, NFS / rpcauth_lookup_credcache()?

On Mon, 2008-11-17 at 13:35 +0100, Max Kellermann wrote:
> On 2008/10/27 16:48, Trond Myklebust <trond.myklebust@....uio.no> wrote:
> > OK. That points a finger at the garbage collector. Does the following
> > patch help at all?
> 
> Hi Trond,
> 
> the server's load seems to be a little bit lower with 2.6.27.6 plus
> your patch, but OProfile still gives me 45% in
> rpcauth_lookup_credcache().  See:
> 
> 1060627  45.1474  (no location information)   rpcauth_lookup_credcache
> 289362   12.3172  auth_generic.c:0            generic_match
> 31886     1.3573  page_alloc.c:0              get_page_from_freelist
> 23932     1.0187  (no location information)   page_fault
> 22176     0.9440  (no location information)   schedule
> 14613     0.6220  (no location information)   __d_lookup
> [...]
> 
> Max

Looking at the above, it seems that you're spending an inordinate amount
of time in generic_match too.
Could you see if the following patch helps?

Cheers
  Trond

-------------------------------------------------------------------------------
From: Trond Myklebust <Trond.Myklebust@...app.com>
SUNRPC: Fix up generic_match()

Cut down on the number of similar copies of group_info.

Signed-off-by: Trond Myklebust <Trond.Myklebust@...app.com>
---

 net/sunrpc/auth_generic.c |   20 ++++++++++++++++++--
 1 files changed, 18 insertions(+), 2 deletions(-)


diff --git a/net/sunrpc/auth_generic.c b/net/sunrpc/auth_generic.c
index 744b79f..4028502 100644
--- a/net/sunrpc/auth_generic.c
+++ b/net/sunrpc/auth_generic.c
@@ -133,13 +133,29 @@ static int
 generic_match(struct auth_cred *acred, struct rpc_cred *cred, int flags)
 {
 	struct generic_cred *gcred = container_of(cred, struct generic_cred, gc_base);
+	int i;
 
 	if (gcred->acred.uid != acred->uid ||
 	    gcred->acred.gid != acred->gid ||
-	    gcred->acred.group_info != acred->group_info ||
 	    gcred->acred.machine_cred != acred->machine_cred)
-		return 0;
+		goto out_nomatch;
+
+	/* Optimisation in the case where pointers are identical... */
+	if (gcred->acred.group_info == acred->group_info)
+		goto out_match;
+
+	/* Slow path... */
+	if (gcred->acred.group_info->ngroups != acred->group_info->ngroups)
+		goto out_nomatch;
+	for (i = 0; i < gcred->acred.group_info->ngroups; i++) {
+		if (GROUP_AT(gcred->acred.group_info, i) !=
+				GROUP_AT(acred->group_info, i))
+			goto out_nomatch;
+	}
+out_match:
 	return 1;
+out_nomatch:
+	return 0;
 }
 
 void __init rpc_init_generic_auth(void)


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