From patchwork Tue Aug 7 09:55:28 2012 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: Pavel Emelyanov X-Patchwork-Id: 175564 X-Patchwork-Delegate: davem@davemloft.net Return-Path: X-Original-To: patchwork-incoming@ozlabs.org Delivered-To: patchwork-incoming@ozlabs.org Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by ozlabs.org (Postfix) with ESMTP id 6CAD62C0095 for ; Tue, 7 Aug 2012 19:55:37 +1000 (EST) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1753817Ab2HGJzf (ORCPT ); Tue, 7 Aug 2012 05:55:35 -0400 Received: from mailhub.sw.ru ([195.214.232.25]:26162 "EHLO relay.sw.ru" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753492Ab2HGJzf (ORCPT ); Tue, 7 Aug 2012 05:55:35 -0400 Received: from [10.30.22.37] ([10.30.22.37]) (authenticated bits=0) by relay.sw.ru (8.13.4/8.13.4) with ESMTP id q779tSiu022577 (version=TLSv1/SSLv3 cipher=DHE-RSA-AES256-SHA bits=256 verify=NO); Tue, 7 Aug 2012 13:55:29 +0400 (MSK) Message-ID: <5020E610.1040808@parallels.com> Date: Tue, 07 Aug 2012 13:55:28 +0400 From: Pavel Emelyanov User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:10.0.1) Gecko/20120209 Thunderbird/10.0.1 MIME-Version: 1.0 To: Eric Dumazet , David Miller CC: "ebiederm@xmission.com" , "netdev@vger.kernel.org" Subject: Re: [PATCH 1/6] hash: Introduce ptr_hash_mix routine References: <501FD0F2.4040609@parallels.com> <501FD11B.6000006@parallels.com> <20120806.134459.954167716448843820.davem@davemloft.net> <5020DBCD.7040806@parallels.com> <1344331716.26674.89.camel@edumazet-glaptop> In-Reply-To: <1344331716.26674.89.camel@edumazet-glaptop> Sender: netdev-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: netdev@vger.kernel.org > I think we should avoid hash_ptr() because its quite expensive > > David suggested to not use the L1_CACHE_SHIFT and instead do a plain : > > static inline u32 ptr_hash_mix(const void *ptr) > { > unsigned long val = (unsigned long)ptr; > > #if BITS_PER_LONG == 64 > val ^= (val >> 32); > #endif > return (u32)val; > } > > By the way we could name this hash32_ptr() instead of ptr_hash_mix() OK. I was under impression, that hash_ptr was balanced from the fast/effective perspective, but I can't argue with you in that area :) So, please, consider the below patch instead of #1 and #2 (the rest ones remain unchanged). Thanks, Pavel From: Pavel Emelyanov Subject: [PATCH 1/5] net: Dont use ifindices in hash fns Eric noticed, that when there will be devices with equal indices, some hash functions that use them will become less effective as they could. Fix this in advance by mixing the net_device address into the hash value instead of the device index. This is true for arp and ndisc hash fns. The netlabel, can and llc ones are also ifindex-based, but that three are init_net-only, thus will not be affected. Many thanks to David and Eric for the hash32_ptr implementation! Signed-off-by: Pavel Emelyanov Signed-off-by: Eric Dumazet --- include/linux/hash.h | 10 ++++++++++ include/net/arp.h | 3 ++- include/net/ndisc.h | 3 ++- 3 files changed, 14 insertions(+), 2 deletions(-) diff --git a/include/linux/hash.h b/include/linux/hash.h index b80506b..24df9e7 100644 --- a/include/linux/hash.h +++ b/include/linux/hash.h @@ -67,4 +67,14 @@ static inline unsigned long hash_ptr(const void *ptr, unsigned int bits) { return hash_long((unsigned long)ptr, bits); } + +static inline u32 hash32_ptr(const void *ptr) +{ + unsigned long val = (unsigned long)ptr; + +#if BITS_PER_LONG == 64 + val ^= (val >> 32); +#endif + return (u32)val; +} #endif /* _LINUX_HASH_H */ diff --git a/include/net/arp.h b/include/net/arp.h index 7f7df93..b630dae 100644 --- a/include/net/arp.h +++ b/include/net/arp.h @@ -3,6 +3,7 @@ #define _ARP_H #include +#include #include @@ -10,7 +11,7 @@ extern struct neigh_table arp_tbl; static inline u32 arp_hashfn(u32 key, const struct net_device *dev, u32 hash_rnd) { - u32 val = key ^ dev->ifindex; + u32 val = key ^ hash32_ptr(dev); return val * hash_rnd; } diff --git a/include/net/ndisc.h b/include/net/ndisc.h index 96a3b5c..980d263 100644 --- a/include/net/ndisc.h +++ b/include/net/ndisc.h @@ -49,6 +49,7 @@ enum { #include #include #include +#include #include @@ -134,7 +135,7 @@ static inline u32 ndisc_hashfn(const void *pkey, const struct net_device *dev, _ { const u32 *p32 = pkey; - return (((p32[0] ^ dev->ifindex) * hash_rnd[0]) + + return (((p32[0] ^ hash32_ptr(dev)) * hash_rnd[0]) + (p32[1] * hash_rnd[1]) + (p32[2] * hash_rnd[2]) + (p32[3] * hash_rnd[3]));