Date: Tue, 07 Mar 2017 21:02:37 +0000 From: bugzilla-noreply@freebsd.org To: freebsd-bugs@FreeBSD.org Subject: [Bug 217618] Enhance hash function in ip_fw_table_algo.c for flow:hash Message-ID: <bug-217618-8@https.bugs.freebsd.org/bugzilla/>
next in thread | raw e-mail | index | archive | help
https://bugs.freebsd.org/bugzilla/show_bug.cgi?id=3D217618 Bug ID: 217618 Summary: Enhance hash function in ip_fw_table_algo.c for flow:hash Product: Base System Version: 11.0-STABLE Hardware: Any OS: Any Status: New Severity: Affects Some People Priority: --- Component: kern Assignee: freebsd-bugs@FreeBSD.org Reporter: lutz@donnerhacke.de While experimenting with some extentions for flow tables, I noticed, that t= he hash function does not separate distinct entries clearly enough. Larger flo= ws tables do reflect external structures and tend to heavily cluster the entri= es on a few hash values (i.e. src-ip and dst-ip are varied both within a netwo= rk). Current code does not even include the protocol number. So I propose to reuse the existing crc32 function for this small amount of data. The probability to have a uniform distributed hash key increases dramatically and overall the lookup is faster than step through a list of entries having the same key. Note: This code depends on a zeroed struct fhashentry*, because it does not select the individual fields. All functions despite ta_prepare_del_fhash do clean the structure. I'm not sure, if this is can cause a problem. --- sys/netpfil/ipfw/ip_fw_table_algo.c (revision 314807) +++ sys/netpfil/ipfw/ip_fw_table_algo.c (working copy) @@ -3163,7 +3176,7 @@ { uint32_t i; - i =3D (f->dip.s_addr) ^ (f->sip.s_addr) ^ (f->e.dport) ^ (f->e.spor= t); + i =3D crc32(f, sizeof(*f)); return (i % (hsize - 1)); } @@ -3173,11 +3186,7 @@ { uint32_t i; - i =3D (f->dip6.__u6_addr.__u6_addr32[2]) ^ - (f->dip6.__u6_addr.__u6_addr32[3]) ^ - (f->sip6.__u6_addr.__u6_addr32[2]) ^ - (f->sip6.__u6_addr.__u6_addr32[3]) ^ - (f->e.dport) ^ (f->e.sport); + i =3D crc32(f, sizeof(*f)); return (i % (hsize - 1)); } --=20 You are receiving this mail because: You are the assignee for the bug.=
Want to link to this message? Use this URL: <https://mail-archive.FreeBSD.org/cgi/mid.cgi?bug-217618-8>