From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from psmtp.com (na3sys010amx137.postini.com [74.125.245.137]) by kanga.kvack.org (Postfix) with SMTP id EA1986B007B for ; Mon, 29 Oct 2012 11:44:20 -0400 (EDT) Received: by mail-ie0-f169.google.com with SMTP id 10so8629360ied.14 for ; Mon, 29 Oct 2012 08:44:20 -0700 (PDT) MIME-Version: 1.0 In-Reply-To: <20121029132931.GC16391@Krystal> References: <1351450948-15618-1-git-send-email-levinsasha928@gmail.com> <1351450948-15618-15-git-send-email-levinsasha928@gmail.com> <20121029132931.GC16391@Krystal> From: Sasha Levin Date: Mon, 29 Oct 2012 11:43:59 -0400 Message-ID: Subject: Re: [PATCH v7 15/16] openvswitch: use new hashtable implementation Content-Type: text/plain; charset=ISO-8859-1 Sender: owner-linux-mm@kvack.org List-ID: To: Mathieu Desnoyers Cc: torvalds@linux-foundation.org, tj@kernel.org, akpm@linux-foundation.org, linux-kernel@vger.kernel.org, linux-mm@kvack.org, paul.gortmaker@windriver.com, davem@davemloft.net, rostedt@goodmis.org, mingo@elte.hu, ebiederm@xmission.com, aarcange@redhat.com, ericvh@gmail.com, netdev@vger.kernel.org, josh@joshtriplett.org, eric.dumazet@gmail.com, axboe@kernel.dk, agk@redhat.com, dm-devel@redhat.com, neilb@suse.de, ccaulfie@redhat.com, teigland@redhat.com, Trond.Myklebust@netapp.com, bfields@fieldses.org, fweisbec@gmail.com, jesse@nicira.com, venkat.x.venkatsubra@oracle.com, ejt@redhat.com, snitzer@redhat.com, edumazet@google.com, linux-nfs@vger.kernel.org, dev@openvswitch.org, rds-devel@oss.oracle.com, lw@cn.fujitsu.com Hi Mathieu, On Mon, Oct 29, 2012 at 9:29 AM, Mathieu Desnoyers wrote: > * Sasha Levin (levinsasha928@gmail.com) wrote: > [...] >> -static struct hlist_head *hash_bucket(struct net *net, const char *name) >> -{ >> - unsigned int hash = jhash(name, strlen(name), (unsigned long) net); >> - return &dev_table[hash & (VPORT_HASH_BUCKETS - 1)]; >> -} >> - >> /** >> * ovs_vport_locate - find a port that has already been created >> * >> @@ -84,13 +76,12 @@ static struct hlist_head *hash_bucket(struct net *net, const char *name) >> */ >> struct vport *ovs_vport_locate(struct net *net, const char *name) >> { >> - struct hlist_head *bucket = hash_bucket(net, name); >> struct vport *vport; >> struct hlist_node *node; >> + int key = full_name_hash(name, strlen(name)); >> >> - hlist_for_each_entry_rcu(vport, node, bucket, hash_node) >> - if (!strcmp(name, vport->ops->get_name(vport)) && >> - net_eq(ovs_dp_get_net(vport->dp), net)) >> + hash_for_each_possible_rcu(dev_table, vport, node, hash_node, key) > > Is applying hash_32() on top of full_name_hash() needed and expected ? Since this was pointed out in several of the patches, I'll answer it just once here. I've intentionally "allowed" double hashing with hash_32 to keep the code simple. hash_32() is pretty simple and gcc optimizes it to be almost nothing, so doing that costs us a multiplication and a shift. On the other hand, we benefit from keeping our code simple - how would we avoid doing this double hash? adding a different hashtable function for strings? or a new function for already hashed keys? I think we benefit a lot from having to mul/shr instead of adding extra lines of code here. Thanks, Sasha -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@kvack.org. For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: email@kvack.org