Return-Path: linux-nfs-owner@vger.kernel.org Received: from mail-qe0-f51.google.com ([209.85.128.51]:52865 "EHLO mail-qe0-f51.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1756207Ab3BUS2t (ORCPT ); Thu, 21 Feb 2013 13:28:49 -0500 Received: by mail-qe0-f51.google.com with SMTP id 6so4538644qea.10 for ; Thu, 21 Feb 2013 10:28:48 -0800 (PST) From: Jeff Layton To: bfields@fieldses.org Cc: linux-nfs@vger.kernel.org Subject: [PATCH v2 4/5] nfsd: report length of the longest hash chain in reply cache stats Date: Thu, 21 Feb 2013 13:28:37 -0500 Message-Id: <1361471318-17971-5-git-send-email-jlayton@redhat.com> In-Reply-To: <1361471318-17971-1-git-send-email-jlayton@redhat.com> References: <1361471318-17971-1-git-send-email-jlayton@redhat.com> Sender: linux-nfs-owner@vger.kernel.org List-ID: So we can get a feel for how effective the hashing function is. As Chuck Lever pointed out to me, it's generally acceptable to do "expensive" stuff when reading the stats since that's a relatively rare activity. When we go to read the file, walk all of the hash chains and count the number of entries in each. Report the length of the longest one. Cc: Chuck Lever Signed-off-by: Jeff Layton --- fs/nfsd/nfscache.c | 23 +++++++++++++++++++++++ 1 file changed, 23 insertions(+) diff --git a/fs/nfsd/nfscache.c b/fs/nfsd/nfscache.c index a5ac9ab..52493cb 100644 --- a/fs/nfsd/nfscache.c +++ b/fs/nfsd/nfscache.c @@ -552,6 +552,28 @@ nfsd_cache_append(struct svc_rqst *rqstp, struct kvec *data) } /* + * Walk each hash chain and count the number of entries. Return the length of + * the longest one. Must be called with the cache_lock held. + */ +static unsigned int +nfsd_repcache_max_chain_len(void) +{ + int i; + struct hlist_node *pos; + unsigned int max = 0; + + for (i = 0; i < HASHSIZE; ++i) { + unsigned int cur = 0; + + hlist_for_each(pos, &cache_hash[i]) + ++cur; + max = max(cur, max); + } + + return max; +} + +/* * Note that fields may be added, removed or reordered in the future. Programs * scraping this file for info should test the labels to ensure they're * getting the correct field. @@ -566,6 +588,7 @@ static int nfsd_reply_cache_stats_show(struct seq_file *m, void *v) seq_printf(m, "cache misses: %u\n", nfsdstats.rcmisses); seq_printf(m, "not cached: %u\n", nfsdstats.rcnocache); seq_printf(m, "checksum misses: %u\n", csum_misses); + seq_printf(m, "max chain len: %u\n", nfsd_repcache_max_chain_len()); spin_unlock(&cache_lock); return 0; } -- 1.7.11.7