Re: High load in 2.6.27, NFS / rpcauth_lookup_credcache()?

Trond Myklebust
2008-11-19T22:31:20Z

On Mon, 2008-11-17 at 13:35 +0100, Max Kellermann wrote:
> On 2008/10/27 16:48, Trond Myklebust <trond.myklebust@fys.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@netapp.com>
SUNRPC: Fix up generic_match()

Cut down on the number of similar copies of group_info.

Signed-off-by: Trond Myklebust <Trond.Myklebust@netapp.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)