From mboxrd@z Thu Jan 1 00:00:00 1970 From: Wang Jian Subject: Re: [RFC] dynamic hash table size & xor hash function for cls_fw Date: Thu, 07 Apr 2005 18:47:08 +0800 Message-ID: <20050407184456.02CC.LARK@linux.net.cn> References: <20050407005519.GS26731@postel.suug.ch> <1112870307.1118.91.camel@jzny.localdomain> Mime-Version: 1.0 Content-Type: text/plain; charset="US-ASCII" Content-Transfer-Encoding: 7bit Cc: Thomas Graf , "David S. Miller" , netdev Return-path: To: hadi@cyberus.ca In-Reply-To: <1112870307.1118.91.camel@jzny.localdomain> Sender: netdev-bounce@oss.sgi.com Errors-to: netdev-bounce@oss.sgi.com List-Id: netdev.vger.kernel.org Hi jamal, I think Thomas decide to only support one hash function at compile time, and no switch at runtime. HSIZE is a constant so the if branch will be optimized by gcc at compile time. only one hash is left. On 07 Apr 2005 06:38:27 -0400, jamal wrote: > On Wed, 2005-04-06 at 20:55, Thomas Graf wrote: > > > > > static __inline__ int fw_hash(u32 handle) > > { > > - return handle&0xFF; > > + if (HTSIZE == 4096) > > + return ((handle >> 24) & 0xFFF) ^ > > + ((handle >> 12) & 0xFFF) ^ > > + (handle & 0xFFF); > > + else if (HTSIZE == 2048) > > + return ((handle >> 22) & 0x7FF) ^ > > + ((handle >> 11) & 0x7FF) ^ > > + (handle & 0x7FF); > > + else if (HTSIZE == 1024) > > + return ((handle >> 20) & 0x3FF) ^ > > + ((handle >> 10) & 0x3FF) ^ > > + (handle & 0x3FF); > > + else if (HTSIZE == 512) > > + return (handle >> 27) ^ > > + ((handle >> 18) & 0x1FF) ^ > > + ((handle >> 9) & 0x1FF) ^ > > + (handle & 0x1FF); > > + else if (HTSIZE == 256) { > > + u8 *t = (u8 *) &handle; > > + return t[0] ^ t[1] ^ t[2] ^ t[3]; > > + } else > > + return handle & (HTSIZE - 1); > > } > > Does HTSIZE change at runtime? How does migrating from one to other take > place? > Also why not have a function pointer with a series of these being > separate instead of doing the if checks? BTW it does seem any one of > those hashes maybe sufficient, no? > > cheers, > jamal -- lark