From mboxrd@z Thu Jan 1 00:00:00 1970 From: Mathieu Desnoyers Subject: Re: [PATCH v7 15/16] openvswitch: use new hashtable implementation Date: Mon, 29 Oct 2012 11:59:57 -0400 Message-ID: <20121029155957.GB18834@Krystal> References: <1351450948-15618-1-git-send-email-levinsasha928@gmail.com> <1351450948-15618-15-git-send-email-levinsasha928@gmail.com> <20121029132931.GC16391@Krystal> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Cc: torvalds-de/tnXTf+JLsfHDXvbKv3WD2FQJk+8+b@public.gmane.org, tj-DgEjT+Ai2ygdnm+yROfE0A@public.gmane.org, akpm-de/tnXTf+JLsfHDXvbKv3WD2FQJk+8+b@public.gmane.org, linux-kernel-u79uwXL29TY76Z2rM5mHXA@public.gmane.org, linux-mm-Bw31MaZKKs3YtjvyW6yDsg@public.gmane.org, paul.gortmaker-CWA4WttNNZF54TAoqtyWWQ@public.gmane.org, davem-fT/PcQaiUtIeIZ0/mPfg9Q@public.gmane.org, rostedt-nx8X9YLhiw1AfugRpC6u6w@public.gmane.org, mingo-X9Un+BFzKDI@public.gmane.org, ebiederm-aS9lmoZGLiVWk0Htik3J/w@public.gmane.org, aarcange-H+wXaHxf7aLQT0dZR+AlfA@public.gmane.org, ericvh-Re5JQEeQqe8AvxtiuMwx3w@public.gmane.org, netdev-u79uwXL29TY76Z2rM5mHXA@public.gmane.org, josh-iaAMLnmF4UmaiuxdJuQwMA@public.gmane.org, eric.dumazet-Re5JQEeQqe8AvxtiuMwx3w@public.gmane.org, axboe-tSWWG44O7X1aa/9Udqfwiw@public.gmane.org, agk-H+wXaHxf7aLQT0dZR+AlfA@public.gmane.org, dm-devel-H+wXaHxf7aLQT0dZR+AlfA@public.gmane.org, neilb-l3A5Bk7waGM@public.gmane.org, ccaulfie-H+wXaHxf7aLQT0dZR+AlfA@public.gmane.org, teigland-H+wXaHxf7aLQT0dZR+AlfA@public.gmane.org, Trond.Myklebust-HgOvQuBEEgTQT0dZR+AlfA@public.gmane.org, bfields-uC3wQj2KruNg9hUCZPvPmw@public.gmane.org, fweisbec-Re5JQEeQqe8AvxtiuMwx3w@public.gmane.org, jesse-l0M0P4e3n4LQT0dZR+AlfA@public.gmane.org, venkat.x.venkatsubra-QHcLZuEGTsvQT0dZR+AlfA@public.gmane.org, ejt-H+wXaHxf7aLQT0dZR+AlfA@public.gmane.org, snitzer-H+wXaHxf7aLQT0dZR+AlfA@public.gmane.org, edumazet-hpIqsD4AKlfQT0dZR+AlfA@public.gmane.org, linux-nfs-u79uwXL29TY76Z2rM5mHXA@public.gmane.org, dev-yBygre7rU0TnMu66kgdUjQ@public.gmane.org, rds-devel-N0ozoZBvEnrZJqsBc5GL+g@public.gmane.org, lw-BthXqXjhjHXQFUHtdCDX3A@public.gmane.org To: Sasha Levin Return-path: Content-Disposition: inline In-Reply-To: Sender: linux-nfs-owner-u79uwXL29TY76Z2rM5mHXA@public.gmane.org List-Id: netdev.vger.kernel.org * Sasha Levin (levinsasha928-Re5JQEeQqe8AvxtiuMwx3w@public.gmane.org) wrote: > Hi Mathieu, > > On Mon, Oct 29, 2012 at 9:29 AM, Mathieu Desnoyers > wrote: > > * Sasha Levin (levinsasha928-Re5JQEeQqe8AvxtiuMwx3w@public.gmane.org) 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. This could be done, as I pointed out in another email within this thread, by changing the "key" argument from add/for_each_possible to an expected "hash" value, and let the caller invoke hash_32() if they want. I doubt this would add a significant amount of complexity for users of this API, but would allow much more flexibility to choose hash functions. Thanks, Mathieu -- Mathieu Desnoyers Operating System Efficiency R&D Consultant EfficiOS Inc. http://www.efficios.com -- To unsubscribe from this list: send the line "unsubscribe linux-nfs" in the body of a message to majordomo-u79uwXL29TY76Z2rM5mHXA@public.gmane.org More majordomo info at http://vger.kernel.org/majordomo-info.html