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Hannes Frederic Sowa 809fa972fd reciprocal_divide: update/correction of the algorithm 
Jakub Zawadzki noticed that some divisions by reciprocal_divide()
were not correct [1][2], which he could also show with BPF code
after divisions are transformed into reciprocal_value() for runtime
invariance which can be passed to reciprocal_divide() later on;
reverse in BPF dump ended up with a different, off-by-one K in
some situations.

This has been fixed by Eric Dumazet in commit aee636c480
("bpf: do not use reciprocal divide"). This follow-up patch
improves reciprocal_value() and reciprocal_divide() to work in
all cases by using Granlund and Montgomery method, so that also
future use is safe and without any non-obvious side-effects.
Known problems with the old implementation were that division by 1
always returned 0 and some off-by-ones when the dividend and divisor
where very large. This seemed to not be problematic with its
current users, as far as we can tell. Eric Dumazet checked for
the slab usage, we cannot surely say so in the case of flex_array.
Still, in order to fix that, we propose an extension from the
original implementation from commit 6a2d7a955d resp. [3][4],
by using the algorithm proposed in "Division by Invariant Integers
Using Multiplication" [5], Torbjörn Granlund and Peter L.
Montgomery, that is, pseudocode for q = n/d where q, n, d is in
u32 universe:

1) Initialization:

  int l = ceil(log_2 d)
  uword m' = floor((1<<32)*((1<<l)-d)/d)+1
  int sh_1 = min(l,1)
  int sh_2 = max(l-1,0)

2) For q = n/d, all uword:

  uword t = (n*m')>>32
  q = (t+((n-t)>>sh_1))>>sh_2

The assembler implementation from Agner Fog [6] also helped a lot
while implementing. We have tested the implementation on x86_64,
ppc64, i686, s390x; on x86_64/haswell we're still half the latency
compared to normal divide.

Joint work with Daniel Borkmann.

  [1] http://www.wireshark.org/~darkjames/reciprocal-buggy.c
  [2] http://www.wireshark.org/~darkjames/set-and-dump-filter-k-bug.c
  [3] https://gmplib.org/~tege/division-paper.pdf
  [4] http://homepage.cs.uiowa.edu/~jones/bcd/divide.html
  [5] http://citeseerx.ist.psu.edu/viewdoc/summary?doi=10.1.1.1.2556
  [6] http://www.agner.org/optimize/asmlib.zip

Reported-by: Jakub Zawadzki <darkjames-ws@darkjames.pl>
Cc: Eric Dumazet <eric.dumazet@gmail.com>
Cc: Austin S Hemmelgarn <ahferroin7@gmail.com>
Cc: linux-kernel@vger.kernel.org
Cc: Jesse Gross <jesse@nicira.com>
Cc: Jamal Hadi Salim <jhs@mojatatu.com>
Cc: Stephen Hemminger <stephen@networkplumber.org>
Cc: Matt Mackall <mpm@selenic.com>
Cc: Pekka Enberg <penberg@kernel.org>
Cc: Christoph Lameter <cl@linux-foundation.org>
Cc: Andy Gospodarek <andy@greyhouse.net>
Cc: Veaceslav Falico <vfalico@redhat.com>
Cc: Jay Vosburgh <fubar@us.ibm.com>
Cc: Jakub Zawadzki <darkjames-ws@darkjames.pl>
Signed-off-by: Daniel Borkmann <dborkman@redhat.com>
Signed-off-by: Hannes Frederic Sowa <hannes@stressinduktion.org>
Signed-off-by: David S. Miller <davem@davemloft.net>
 		2014-01-21 23:17:20 -08:00
..
9p for-linus-3.12-merge minor 9p fixes and tweaks for 3.12 merge window 2013-09-11 12:34:13 -07:00
bluetooth Bluetooth: Add quirk for disabling Delete Stored Link Key command 2014-01-04 20:10:40 +02:00
caif caif_hsi.h: Remove extern from function prototypes 2013-09-23 16:29:41 -04:00
irda include/net/: Fix FSF address in file headers 2013-12-06 12:37:56 -05:00
iucv af_iucv: fix recvmsg by replacing skb_pull() function 2013-04-08 17:16:57 -04:00
netfilter netfilter: nf_tables: rename nft_do_chain_pktinfo() to nft_do_chain() 2014-01-09 20:17:16 +01:00
netns ipv6: add flowlabel_consistency sysctl 2014-01-19 17:12:31 -08:00
nfc Merge branch 'master' of git://git.kernel.org/pub/scm/linux/kernel/git/linville/wireless-next into for-davem 2014-01-17 14:43:17 -05:00
phonet net: remove my future former mail address 2012-06-17 16:29:38 -07:00
sctp sctp: remove macros sctp_bh_[un]lock_sock 2014-01-21 18:41:36 -08:00
tc_act include/net/: Fix FSF address in file headers 2013-12-06 12:37:56 -05:00
Space.h drivers: net: Include new header file in sbni.c 2013-12-19 18:51:20 -05:00
act_api.h net_sched: act: export tcf_hash_search() instead of tcf_hash_lookup() 2014-01-21 14:43:16 -08:00
addrconf.h neigh: ipv6: respect default values set before an address is assigned to device 2013-12-09 20:56:12 -05:00
af_ieee802154.h af_ieee802154: add support for WANT_ACK socket option 2009-08-12 21:54:50 -07:00
af_rxrpc.h af_rxrpc.h: Remove extern from function prototypes 2013-07-31 17:50:01 -07:00
af_unix.h af_unix: improve STREAM behavior with fragmented memory 2013-08-10 01:16:44 -07:00
af_vsock.h VSOCK: Move af_vsock.h and vsock_addr.h to include/net 2013-07-27 22:14:06 -07:00
ah.h ipsec: update MAX_AH_AUTH_LEN to support sha512 2011-01-13 21:48:25 -08:00
arp.h arp: make arp_invalidate static 2013-12-28 17:02:46 -05:00
atmclip.h atm: clip: Use device neigh support on top of "arp_tbl". 2011-11-30 18:51:03 -05:00
ax25.h ax25.h: Remove extern from function prototypes 2013-07-31 17:50:02 -07:00
ax88796.h ax88796: Add method to take MAC from platform data 2009-03-24 23:32:03 -07:00
busy_poll.h net: add cpu_relax to busy poll loop 2013-08-28 17:45:48 -04:00
cfg80211-wext.h cfg80211: remove unused wext handler exports 2011-08-08 14:26:29 -04:00
cfg80211.h cfg80211: Add a function to get the number of supported channels 2014-01-09 14:24:24 +01:00
checksum.h net: checksum: fix warning in skb_checksum 2013-11-04 15:27:08 -05:00
cipso_ipv4.h cipso: cleanup cipso_v4_translate() when !CONFIG_NETLABEL 2013-12-10 17:56:54 -05:00
cls_cgroup.h net: net_cls: move cgroupfs classid handling into core 2014-01-03 23:41:41 +01:00
codel.h net: introduce reciprocal_scale helper and convert users 2014-01-21 23:17:20 -08:00
compat.h compat.h: Remove extern from function prototypes 2013-09-20 14:49:32 -04:00
datalink.h
…
dcbevent.h include/net/: Fix FSF address in file headers 2013-12-06 12:37:56 -05:00
dcbnl.h include/net/: Fix FSF address in file headers 2013-12-06 12:37:56 -05:00
dn.h decnet (dn*.h): Remove extern from function prototypes 2013-09-20 14:49:32 -04:00
dn_dev.h dn_dev: add support for IFA_FLAGS nl attribute 2013-12-10 21:50:00 -05:00
dn_fib.h decnet (dn*.h): Remove extern from function prototypes 2013-09-20 14:49:32 -04:00
dn_neigh.h decnet (dn*.h): Remove extern from function prototypes 2013-09-20 14:49:32 -04:00
dn_nsp.h decnet (dn*.h): Remove extern from function prototypes 2013-09-20 14:49:32 -04:00
dn_route.h decnet (dn*.h): Remove extern from function prototypes 2013-09-20 14:49:32 -04:00
dsa.h dsa: Include linux/if_ether.h to fix build error 2011-12-01 11:41:06 -05:00
dsfield.h ipv6: Optimize ipv6_change_dsfield(). 2013-01-09 23:59:53 -08:00
dst.h net: Add utility functions to clear rxhash 2013-12-17 16:36:21 -05:00
dst_ops.h net: Fix warnings in dst_ops.h 2012-07-19 10:43:03 -07:00
esp.h net: move pskb_put() to core code 2013-11-07 19:28:58 -05:00
ethoc.h net: Add support for the OpenCores 10/100 Mbps Ethernet MAC. 2009-03-27 00:16:21 -07:00
fib_rules.h fib_rules.h: Remove extern from function prototypes 2013-09-20 14:49:33 -04:00
firewire.h firewire net, ipv4 arp: Extend hardware address and remove driver-level packet inspection. 2013-03-26 12:32:13 -04:00
flow.h net: Remove FLOWI_FLAG_CAN_SLEEP 2013-12-06 07:24:39 +01:00
flow_keys.h flow_dissector: factor out the ports extraction in skb_flow_get_ports 2013-10-03 15:36:37 -04:00
garp.h garp.h: Remove extern from function prototypes 2013-09-20 14:49:33 -04:00
gen_stats.h gen_stats.h: Remove extern from function prototypes 2013-09-20 14:49:33 -04:00
genetlink.h genl: Add genlmsg_new_unicast() for unicast message allocation 2014-01-06 15:51:53 -08:00
gre.h gre_offload: statically build GRE offloading support 2014-01-06 20:28:34 -05:00
gro_cells.h gro: Fix kcalloc argument order 2013-01-27 22:46:33 -05:00
icmp.h icmp.h: Remove extern from function prototypes 2013-09-20 14:49:33 -04:00
ieee80211_radiotap.h mac80211: add radiotap flag and handling for 5/10 MHz 2013-07-16 09:58:05 +03:00
ieee802154.h 6LoWPAN: add fragmentation support 2011-11-14 00:19:42 -05:00
ieee802154_netdev.h ieee802154/nl-mac.c: make some MLME operations optional 2013-04-08 12:00:16 -04:00
if_inet6.h Merge git://git.kernel.org/pub/scm/linux/kernel/git/davem/net 2014-01-18 00:55:41 -08:00
inet6_connection_sock.h inet*.h: Remove extern from function prototypes 2013-09-21 14:01:38 -04:00
inet6_hashtables.h ipv6: split inet6_ehashfn to hash functions per compilation unit 2013-10-19 19:45:34 -04:00
inet_common.h inet*.h: Remove extern from function prototypes 2013-09-21 14:01:38 -04:00
inet_connection_sock.h inet*.h: Remove extern from function prototypes 2013-09-21 14:01:38 -04:00
inet_ecn.h net: Correct comparisons and calculations using skb->tail and skb-transport_header 2013-05-28 23:49:07 -07:00
inet_frag.h inet: remove old fragmentation hash initializing 2013-10-23 17:01:41 -04:00
inet_hashtables.h tcp/dccp: remove twchain 2013-10-08 23:19:24 -04:00
inet_sock.h inet: convert inet_ehash_secret and ipv6_hash_secret to net_get_random_once 2013-10-19 19:45:35 -04:00
inet_timewait_sock.h ipv6: tcp: fix flowlabel value in ACK messages send from TIME_WAIT 2014-01-17 17:56:33 -08:00
inetpeer.h ipv4: remove unused function 2013-12-28 17:03:20 -05:00
ip.h ipv6: make IPV6_RECVPKTINFO work for ipv4 datagrams 2014-01-19 19:53:18 -08:00
ip6_checksum.h net: fix build errors if ipv6 is disabled 2013-10-09 13:04:03 -04:00
ip6_fib.h ipv6: remove prune parameter for fib6_clean_all 2014-01-02 03:30:35 -05:00
ip6_route.h IPv6: add the option to use anycast addresses as source addresses in echo reply 2014-01-07 15:51:39 -05:00
ip6_tunnel.h net: unify the pcpu_tstats and br_cpu_netstats as one 2014-01-04 20:10:24 -05:00
ip_fib.h ip*.h: Remove extern from function prototypes 2013-09-21 14:01:38 -04:00
ip_tunnels.h ipv4: fix a dst leak in tunnels 2014-01-17 18:36:39 -08:00
ip_vs.h netfilter: push reasm skb through instead of original frag skbs 2013-11-11 00:19:35 -05:00
ipcomp.h percpu: add __percpu sparse annotations to net 2010-02-16 23:05:38 -08:00
ipconfig.h
…
ipv6.h ipv6: protect protocols not handling ipv4 from v4 connection/bind attempts 2014-01-21 16:59:19 -08:00
ipx.h ipx.h: Remove extern from function prototypes 2013-09-21 14:01:38 -04:00
iw_handler.h iw_handler.h: Remove extern from function prototypes 2013-09-21 14:01:39 -04:00
lapb.h lapb.h: Remove extern from function prototypes 2013-09-21 14:01:38 -04:00
lib80211.h hostap: Don't use create_proc_read_entry() 2013-04-29 15:41:56 -04:00
llc.h llc: make lock static 2014-01-03 20:56:48 -05:00
llc_c_ac.h llc*.h: Remove extern from function prototypes 2013-09-21 14:01:38 -04:00
llc_c_ev.h llc*.h: Remove extern from function prototypes 2013-09-21 14:01:38 -04:00
llc_c_st.h
…
llc_conn.h llc*.h: Remove extern from function prototypes 2013-09-21 14:01:38 -04:00
llc_if.h llc*.h: Remove extern from function prototypes 2013-09-21 14:01:38 -04:00
llc_pdu.h net: llc: fix order of evaluation in llc_conn_ac_inc_vr_by_1 2014-01-01 22:22:43 -05:00
llc_s_ac.h llc*.h: Remove extern from function prototypes 2013-09-21 14:01:38 -04:00
llc_s_ev.h llc*.h: Remove extern from function prototypes 2013-09-21 14:01:38 -04:00
llc_s_st.h
…
llc_sap.h llc*.h: Remove extern from function prototypes 2013-09-21 14:01:38 -04:00
mac80211.h mac80211: handle MMPDUs at EOSP correctly 2014-01-10 09:50:02 +01:00
mac802154.h mac802154: correct a typo in ieee802154_alloc_device() prototype 2013-10-21 18:56:23 -04:00
mip6.h include/net/: Fix FSF address in file headers 2013-12-06 12:37:56 -05:00
mld.h net: ipv6: mld: get rid of MLDV2_MRC and simplify calculation 2013-09-04 14:53:20 -04:00
mrp.h Merge git://git.kernel.org/pub/scm/linux/kernel/git/davem/net 2013-10-01 17:06:14 -04:00
ndisc.h ndisc.h: Remove extern from function prototypes 2013-09-21 14:01:39 -04:00
neighbour.h neigh: use NEIGH_VAR_INIT in ndo_neigh_setup functions. 2014-01-16 11:31:58 -08:00
net_namespace.h netfilter: nf_tables: complete net namespace support 2013-10-14 18:00:59 +02:00
net_ratelimit.h net: Kill ratelimit.h dependency in linux/net.h 2011-05-27 13:41:33 -04:00
netdma.h
…
netevent.h netevent/netlink.h: Remove extern from function prototypes 2013-09-21 14:01:39 -04:00
netlabel.h include/net/: Fix FSF address in file headers 2013-12-06 12:37:56 -05:00
netlink.h netevent/netlink.h: Remove extern from function prototypes 2013-09-21 14:01:39 -04:00
netprio_cgroup.h net: netprio: rename config to be more consistent with cgroup configs 2014-01-03 23:41:42 +01:00
netrom.h netrom.h: Remove extern from function prototypes 2013-09-21 14:01:39 -04:00
nexthop.h
…
nl802154.h ieee802154: add support for channel pages from IEEE 802.15.4-2006 2009-08-19 23:08:22 +04:00
p8022.h p8022.h: Remove extern from function prototypes 2013-09-21 14:01:39 -04:00
ping.h ipv6: make IPV6_RECVPKTINFO work for ipv4 datagrams 2014-01-19 19:53:18 -08:00
pkt_cls.h net_sched: optimize tcf_match_indev() 2014-01-13 11:50:15 -08:00
pkt_sched.h pkt_sched: give visibility to mq slave qdiscs 2013-12-09 19:54:47 -05:00
protocol.h net: Add GRO support for UDP encapsulating protocols 2014-01-21 18:05:04 -08:00
psnap.h psnap.h: Remove extern from function prototypes 2013-09-23 01:51:08 -04:00
raw.h raw/rawv6.h: Remove extern from function prototypes 2013-09-23 01:51:08 -04:00
rawv6.h raw/rawv6.h: Remove extern from function prototypes 2013-09-23 01:51:08 -04:00
red.h reciprocal_divide: update/correction of the algorithm 2014-01-21 23:17:20 -08:00
regulatory.h cfg80211: make regulatory_hint() remove REGULATORY_CUSTOM_REG 2014-01-13 14:46:58 -05:00
request_sock.h inet: includes a sock_common in request_sock 2013-10-10 00:08:07 -04:00
rose.h rose.h: Remove extern from function prototypes 2013-09-23 01:51:08 -04:00
route.h ipv4: introduce ip_dst_mtu_maybe_forward and protect forwarding path against pmtu spoofing 2014-01-13 11:22:54 -08:00
rtnetlink.h netlink: cleanup rntl_af_register 2014-01-01 23:42:19 -05:00
sch_generic.h net_sched: add struct net pointer to tcf_proto_ops->dump 2014-01-13 11:50:14 -08:00
scm.h scm.h: Remove extern from function prototypes 2013-09-23 01:51:09 -04:00
secure_seq.h Merge git://git.kernel.org/pub/scm/linux/kernel/git/davem/net 2013-10-01 17:06:14 -04:00
slhc_vj.h
…
snmp.h net: avoid reloads in SNMP_UPD_PO_STATS 2012-08-06 13:40:47 -07:00
sock.h Merge git://git.kernel.org/pub/scm/linux/kernel/git/pablo/nf-next 2014-01-05 20:18:50 -05:00
stp.h stp.h: Remove extern from function prototypes 2013-09-23 01:51:09 -04:00
tcp.h tcp: make local functions static 2013-12-29 16:34:24 -05:00
tcp_memcontrol.h tcp_memcontrol: Kill struct tcp_memcontrol 2013-10-21 18:43:02 -04:00
tcp_states.h
…
timewait_sock.h [PATCH] tcp: Cache inetpeer in timewait socket, and only when necessary. 2012-06-09 14:56:12 -07:00
transp_v6.h ipv6: make IPV6_RECVPKTINFO work for ipv4 datagrams 2014-01-19 19:53:18 -08:00
udp.h udp: Remove unnecessary semicolon from do{}while (0) macro 2013-11-07 02:14:33 -05:00
udplite.h udplite.h: Remove extern from function prototypes 2013-09-23 16:29:40 -04:00
vsock_addr.h VSOCK: Move af_vsock.h and vsock_addr.h to include/net 2013-07-27 22:14:06 -07:00
vxlan.h net: Add GRO support for vxlan traffic 2014-01-21 18:05:04 -08:00
wext.h wext.h: Remove extern from function prototypes 2013-09-23 16:29:40 -04:00
wimax.h wimax.h: Remove extern from function prototypes 2013-09-23 16:29:41 -04:00
wpan-phy.h mac802154: monitor device support 2012-05-16 15:17:08 -04:00
x25.h x25.h: Remove extern from function prototypes 2013-09-23 16:29:41 -04:00
x25device.h X25: Add if_x25.h and x25 to device identifiers 2010-04-22 16:12:36 -07:00
xfrm.h {pktgen, xfrm} Introduce xfrm_state_lookup_byspi for pktgen 2014-01-03 07:29:12 +01:00