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Date: Sun, 29 Dec 2013 23:05:04 +0100 (CET) From: Julia Lawall <julia.lawall@...6.fr> To: Joe Perches <joe@...ches.com> cc: Julia Lawall <julia.lawall@...6.fr>, Eric Dumazet <eric.dumazet@...il.com>, Ding Tianhong <dingtianhong@...wei.com>, "David S. Miller" <davem@...emloft.net>, Netdev <netdev@...r.kernel.org>, "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org> Subject: Re: [PATCH net-next 19/20] net: plip: slight optimization of addr compare > Hi Julia. > > Maybe this explanation is helpful? > > ethernet addresses are u8[6] (48 bits) > > ether_addr_equal_64bits gets passed a pointer to u8[8] > and is more efficient on 64 bit architectures than > ether_addr_equal because the test can be done with a > single compare and shift. > > The idea is not to access past the end of the ethernet > address as appropriate (think pointer to eeprom or other > such end-of-addressable memory conditions) > > If a struct containing an ethernet address has additional > members after the ethernet address, or the u8[6] address > passed to ether_addr_equal is not going to access past > the end of memory or the structure, then > ether_addr_equal_64bits should be used in lieu of > ether_addr_equal. After some work on getting more include files to be taken into account, I get the following list of cases where both arguments have the form of a field reference, the field has array type, and the field is not at the end of the structure. I guess these are all candidates for ether_addr_equal_64bits (assuming that they correctly do satisfy these properties)? Most of the uses of ether_addr_equal unfortunately take at least one pointer as an argument. If the pointer is a parameter one has to check all of the calls sites. If the function is static, this is perhaps not too bad, but from looking at some examples, it seems that this is often not the case. There seem to also be quite a number of comparisons that use memcmp rather than ether_addr_equal. It seems that using ether_addr_equal would require knowing about alignment. In some cases, the structure field declaration explicitly mentions alignment. I'm not sure how to be sure that it holds otherwise. In particular, many of the relevant structures are declared as __packed. Perhaps that is also an issue for using ether_addr_equal_64bits? julia >From linux-next of 20131224. file drivers/scsi/fcoe/fcoe_ctlr.c on line 1524 file drivers/scsi/fcoe/fcoe_ctlr.c on line 1528 file drivers/scsi/fcoe/fcoe_ctlr.c on line 342 file drivers/scsi/fcoe/fcoe_ctlr.c on line 1042 file drivers/scsi/fcoe/fcoe_sysfs.c on line 660 file drivers/scsi/fcoe/fcoe.c on line 1465 file drivers/net/wireless/rtlwifi/ps.c on line 926 file drivers/net/wireless/rtlwifi/ps.c on line 481 file drivers/net/wireless/rtlwifi/base.c on line 1296 file drivers/net/wireless/rtlwifi/base.c on line 1784 file drivers/net/wireless/p54/txrx.c on line 311 file drivers/net/wireless/rt2x00/rt2x00dev.c on line 568 file drivers/net/wireless/rt2x00/rt2x00dev.c on line 571 file drivers/net/wireless/ipw2x00/libipw_rx.c on line 1471 file drivers/net/wireless/ath/carl9170/rx.c on line 605 file drivers/net/wireless/ath/carl9170/rx.c on line 606 file drivers/net/wireless/ath/carl9170/rx.c on line 539 file drivers/net/wireless/ath/ath9k/htc_drv_txrx.c on line 1080 file drivers/net/wireless/ath/ath9k/recv.c on line 985 file drivers/net/wireless/ath/ath5k/base.c on line 1248 file drivers/net/wireless/ath/ath5k/base.c on line 1312 file drivers/net/wireless/iwlegacy/3945.c on line 472 file drivers/net/wireless/iwlegacy/3945.c on line 469 file drivers/net/wireless/iwlegacy/common.c on line 3749 file drivers/net/wireless/iwlegacy/common.c on line 3750 file drivers/net/wireless/iwlegacy/common.c on line 3751 file drivers/net/wireless/mwl8k.c on line 1261 file drivers/net/wireless/at76c50x-usb.c on line 1724 file drivers/net/wireless/iwlwifi/dvm/rxon.c on line 878 file drivers/net/wireless/iwlwifi/dvm/rxon.c on line 879 file drivers/net/wireless/iwlwifi/dvm/rxon.c on line 880 file drivers/net/wireless/iwlwifi/dvm/rx.c on line 783 file drivers/net/ethernet/qlogic/qlcnic/qlcnic_io.c on line 334 file drivers/net/ethernet/qlogic/qlcnic/qlcnic_io.c on line 580 file drivers/net/vxlan.c on line 1371 file drivers/staging/slicoss/slicoss.c on line 790 file drivers/staging/vt6656/wpactl.c on line 230 file drivers/staging/vt6656/dpc.c on line 357 file drivers/staging/vt6656/dpc.c on line 369 file net/bluetooth/bnep/core.c on line 407 file net/bluetooth/bnep/core.c on line 410 file net/wireless/scan.c on line 636 file net/wireless/mlme.c on line 561 file net/wireless/mlme.c on line 575 file net/wireless/mlme.c on line 588 file net/hsr/hsr_framereg.c on line 88 file net/hsr/hsr_framereg.c on line 187 file net/hsr/hsr_framereg.c on line 90 file net/hsr/hsr_framereg.c on line 178 file net/802/stp.c on line 49 file net/mac80211/tx.c on line 1693 file net/mac80211/mesh.c on line 1055 file net/mac80211/mesh.c on line 1005 file net/mac80211/scan.c on line 187 file net/mac80211/scan.c on line 188 file net/mac80211/mlme.c on line 2584 file net/mac80211/mlme.c on line 4036 file net/mac80211/mlme.c on line 3827 file net/mac80211/mlme.c on line 2784 file net/mac80211/mlme.c on line 2814 file net/mac80211/mlme.c on line 2217 file net/mac80211/mlme.c on line 2245 file net/mac80211/mlme.c on line 2708 file net/mac80211/mlme.c on line 2712 file net/mac80211/mlme.c on line 2695 file net/mac80211/iface.c on line 288 file net/mac80211/rx.c on line 1910 file net/mac80211/rx.c on line 1641 file net/mac80211/rx.c on line 1642 file net/mac80211/rx.c on line 3104 file net/mac80211/rx.c on line 2341 file net/mac80211/rx.c on line 2521 file net/mac80211/rx.c on line 2340 file net/mac80211/rx.c on line 2335 file net/mac80211/rx.c on line 3093 file net/mac80211/rx.c on line 3111 file net/mac80211/rx.c on line 3127 file net/mac80211/rx.c on line 3137 file net/mac80211/rx.c on line 3147 file net/mac80211/rx.c on line 3168 file net/mac80211/rx.c on line 3103 file net/mac80211/rx.c on line 2146 file net/mac80211/sta_info.c on line 416 file net/mac80211/status.c on line 595 file net/mac80211/ibss.c on line 1126 file net/mac80211/ibss.c on line 1018 file net/mac80211/ibss.c on line 1437 -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@...r.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
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