In arch/i386/makefile we have :
cflags-$(CONFIG_MPENTIUMII) += -march=i686 $(call
cc-option,-mtune=pentium2)
cflags-$(CONFIG_MPENTIUMIII) += -march=i686 $(call
cc-option,-mtune=pentium3)
cflags-$(CONFIG_MPENTIUMM) += -march=i686 $(call
cc-option,-mtune=pentium3)
cflags-$(CONFIG_MPENTIUM4) += -march=i686 $(call
cc-option,-mtune=pentium4)
According to the gcc 3.x doc, the -mtune is not avaliable for i686
and, indeed, with 3.3.5 no -mtune is generated/used (make V=1).
This, of course, heavily penalizes P4's (the notorious inc/dec).
Margit
On Tuesday 13 September 2005 15:04, Margit Schubert-While wrote:
> In arch/i386/makefile we have :
> cflags-$(CONFIG_MPENTIUMII) ? ? += -march=i686 $(call
> cc-option,-mtune=pentium2)
> cflags-$(CONFIG_MPENTIUMIII) ? ?+= -march=i686 $(call
> cc-option,-mtune=pentium3)
> cflags-$(CONFIG_MPENTIUMM) ? ? ?+= -march=i686 $(call
> cc-option,-mtune=pentium3)
> cflags-$(CONFIG_MPENTIUM4) ? ? ?+= -march=i686 $(call
> cc-option,-mtune=pentium4)
>
> According to the gcc 3.x doc, the -mtune is not avaliable for i686
> and, indeed, with 3.3.5 no -mtune is generated/used (make V=1).
That's correct, gcc 3.4 started the -mtune flag. Chances are if you really
want the -mtune optimizations you're going to have to upgrade to gcc 3.4 or
greater.
> This, of course, heavily penalizes P4's (the notorious inc/dec).
Are you referring to cpu cycle counts? Is there certain code that causes the
kernel to perform that unfavorably by a large scale?
> Margit
Chris White
On Wed, 14 Sep 2005, Chris White wrote:
> That's correct, gcc 3.4 started the -mtune flag. Chances are if you really
> want the -mtune optimizations you're going to have to upgrade to gcc 3.4 or
> greater.
>
> > This, of course, heavily penalizes P4's (the notorious inc/dec).
>
> Are you referring to cpu cycle counts? Is there certain code that causes the
> kernel to perform that unfavorably by a large scale?
It's documented as being suboptimal to use inc/dec due to it modifying all
of eflags resulting in dependency related stalls. add/sub only modifies
one bit of eflags so is more optimal. However there is a problem of
increased code size with add/sub.
But i've never benchmarked all of this ;)
On Wednesday 14 September 2005 09:48, Zwane Mwaikambo wrote:
> On Wed, 14 Sep 2005, Chris White wrote:
>
> > That's correct, gcc 3.4 started the -mtune flag. Chances are if you really
> > want the -mtune optimizations you're going to have to upgrade to gcc 3.4 or
> > greater.
> >
> > > This, of course, heavily penalizes P4's (the notorious inc/dec).
> >
> > Are you referring to cpu cycle counts? Is there certain code that causes the
> > kernel to perform that unfavorably by a large scale?
>
> It's documented as being suboptimal to use inc/dec due to it modifying all
> of eflags resulting in dependency related stalls. add/sub only modifies
> one bit of eflags so is more optimal. However there is a problem of
?! add/sub doesn't modify "only one bit in eflags", it modifies all.
In fact, it's dec/inc which does not modify all bits.
It doesn't touch 'carry' bit (IIRC).
If inc/dec is slower on P4, it must be just another P4 quirk.
> increased code size with add/sub.
>
> But i've never benchmarked all of this ;)
I don't even have one to test this.
--
vda
At 14:14 14.09.2005 +0900, Chris scribeth:
>On Tuesday 13 September 2005 15:04, Margit Schubert-While wrote:
> > In arch/i386/makefile we have :
> > cflags-$(CONFIG_MPENTIUMII) += -march=i686 $(call
> > cc-option,-mtune=pentium2)
> > cflags-$(CONFIG_MPENTIUMIII) += -march=i686 $(call
> > cc-option,-mtune=pentium3)
> > cflags-$(CONFIG_MPENTIUMM) += -march=i686 $(call
> > cc-option,-mtune=pentium3)
> > cflags-$(CONFIG_MPENTIUM4) += -march=i686 $(call
> > cc-option,-mtune=pentium4)
> >
> > According to the gcc 3.x doc, the -mtune is not avaliable for i686
> > and, indeed, with 3.3.5 no -mtune is generated/used (make V=1).
>
>That's correct, gcc 3.4 started the -mtune flag. Chances are if you really
>want the -mtune optimizations you're going to have to upgrade to gcc 3.4 or
>greater.
Hmphh.
-mtune is the replacement for -mcpu, correct ?
> > This, of course, heavily penalizes P4's (the notorious inc/dec).
>
>Are you referring to cpu cycle counts? Is there certain code that causes the
>kernel to perform that unfavorably by a large scale?
Not only that ->
2.6.14-rc1, gcc 3.3.5, -march=, fairly minimal server config (see below)
i686:
size vmlinux
text data bss dec hex filename
2903555 433644 341072 3678271 38203f vmlinux
pentium4:
size vmlinux
text data bss dec hex filename
2704100 433644 341072 3478816 351520 vmlinux
Margit
.config
CONFIG_X86=y
CONFIG_SEMAPHORE_SLEEPERS=y
CONFIG_MMU=y
CONFIG_UID16=y
CONFIG_GENERIC_ISA_DMA=y
CONFIG_GENERIC_IOMAP=y
CONFIG_ARCH_MAY_HAVE_PC_FDC=y
CONFIG_EXPERIMENTAL=y
CONFIG_CLEAN_COMPILE=y
CONFIG_LOCK_KERNEL=y
CONFIG_INIT_ENV_ARG_LIMIT=32
CONFIG_LOCALVERSION="-sim5"
CONFIG_SWAP=y
CONFIG_SYSVIPC=y
CONFIG_POSIX_MQUEUE=y
CONFIG_SYSCTL=y
CONFIG_HOTPLUG=y
CONFIG_KOBJECT_UEVENT=y
CONFIG_IKCONFIG=y
CONFIG_IKCONFIG_PROC=y
CONFIG_INITRAMFS_SOURCE=""
CONFIG_KALLSYMS=y
CONFIG_PRINTK=y
CONFIG_BUG=y
CONFIG_BASE_FULL=y
CONFIG_FUTEX=y
CONFIG_EPOLL=y
CONFIG_SHMEM=y
CONFIG_CC_ALIGN_FUNCTIONS=0
CONFIG_CC_ALIGN_LABELS=0
CONFIG_CC_ALIGN_LOOPS=0
CONFIG_CC_ALIGN_JUMPS=0
CONFIG_BASE_SMALL=0
CONFIG_MODULES=y
CONFIG_MODULE_UNLOAD=y
CONFIG_MODULE_FORCE_UNLOAD=y
CONFIG_OBSOLETE_MODPARM=y
CONFIG_MODVERSIONS=y
CONFIG_MODULE_SRCVERSION_ALL=y
CONFIG_KMOD=y
CONFIG_STOP_MACHINE=y
CONFIG_X86_PC=y
CONFIG_MPENTIUM4=y
CONFIG_X86_CMPXCHG=y
CONFIG_X86_XADD=y
CONFIG_X86_L1_CACHE_SHIFT=7
CONFIG_RWSEM_XCHGADD_ALGORITHM=y
CONFIG_GENERIC_CALIBRATE_DELAY=y
CONFIG_X86_WP_WORKS_OK=y
CONFIG_X86_INVLPG=y
CONFIG_X86_BSWAP=y
CONFIG_X86_POPAD_OK=y
CONFIG_X86_GOOD_APIC=y
CONFIG_X86_INTEL_USERCOPY=y
CONFIG_X86_USE_PPRO_CHECKSUM=y
CONFIG_HPET_TIMER=y
CONFIG_HPET_EMULATE_RTC=y
CONFIG_SMP=y
CONFIG_NR_CPUS=4
CONFIG_SCHED_SMT=y
CONFIG_PREEMPT_NONE=y
CONFIG_X86_LOCAL_APIC=y
CONFIG_X86_IO_APIC=y
CONFIG_X86_TSC=y
CONFIG_X86_MCE=y
CONFIG_X86_MCE_P4THERMAL=y
CONFIG_MICROCODE=m
CONFIG_X86_MSR=m
CONFIG_X86_CPUID=m
CONFIG_EDD=m
CONFIG_DELL_RBU=m
CONFIG_DCDBAS=m
CONFIG_HIGHMEM64G=y
CONFIG_HIGHMEM=y
CONFIG_X86_PAE=y
CONFIG_SELECT_MEMORY_MODEL=y
CONFIG_FLATMEM_MANUAL=y
CONFIG_FLATMEM=y
CONFIG_FLAT_NODE_MEM_MAP=y
CONFIG_HIGHPTE=y
CONFIG_MTRR=y
CONFIG_IRQBALANCE=y
CONFIG_HAVE_DEC_LOCK=y
CONFIG_SECCOMP=y
CONFIG_HZ_250=y
CONFIG_HZ=250
CONFIG_PHYSICAL_START=0x100000
CONFIG_PM=y
CONFIG_SOFTWARE_SUSPEND=y
CONFIG_PM_STD_PARTITION=""
CONFIG_ACPI=y
CONFIG_ACPI_AC=m
CONFIG_ACPI_BATTERY=m
CONFIG_ACPI_BUTTON=m
CONFIG_ACPI_VIDEO=m
CONFIG_ACPI_FAN=m
CONFIG_ACPI_PROCESSOR=m
CONFIG_ACPI_THERMAL=m
CONFIG_ACPI_BLACKLIST_YEAR=0
CONFIG_ACPI_EC=y
CONFIG_ACPI_POWER=y
CONFIG_ACPI_SYSTEM=y
CONFIG_X86_PM_TIMER=y
CONFIG_ACPI_CONTAINER=m
CONFIG_APM=y
CONFIG_APM_DO_ENABLE=y
CONFIG_APM_DISPLAY_BLANK=y
CONFIG_APM_ALLOW_INTS=y
CONFIG_PCI=y
CONFIG_PCI_GOANY=y
CONFIG_PCI_BIOS=y
CONFIG_PCI_DIRECT=y
CONFIG_PCI_MMCONFIG=y
CONFIG_PCIEPORTBUS=y
CONFIG_PCI_MSI=y
CONFIG_ISA_DMA_API=y
CONFIG_BINFMT_ELF=y
CONFIG_BINFMT_AOUT=m
CONFIG_BINFMT_MISC=m
CONFIG_NET=y
CONFIG_PACKET=m
CONFIG_PACKET_MMAP=y
CONFIG_UNIX=y
CONFIG_XFRM=y
CONFIG_XFRM_USER=m
CONFIG_NET_KEY=m
CONFIG_INET=y
CONFIG_IP_MULTICAST=y
CONFIG_IP_ADVANCED_ROUTER=y
CONFIG_ASK_IP_FIB_HASH=y
CONFIG_IP_FIB_HASH=y
CONFIG_IP_MULTIPLE_TABLES=y
CONFIG_IP_ROUTE_FWMARK=y
CONFIG_IP_ROUTE_MULTIPATH=y
CONFIG_IP_ROUTE_VERBOSE=y
CONFIG_NET_IPIP=m
CONFIG_NET_IPGRE=m
CONFIG_NET_IPGRE_BROADCAST=y
CONFIG_IP_MROUTE=y
CONFIG_IP_PIMSM_V1=y
CONFIG_IP_PIMSM_V2=y
CONFIG_SYN_COOKIES=y
CONFIG_INET_AH=m
CONFIG_INET_ESP=m
CONFIG_INET_IPCOMP=m
CONFIG_INET_TUNNEL=m
CONFIG_INET_DIAG=y
CONFIG_INET_TCP_DIAG=y
CONFIG_TCP_CONG_BIC=y
CONFIG_IP_VS=m
CONFIG_IP_VS_TAB_BITS=12
CONFIG_IP_VS_PROTO_TCP=y
CONFIG_IP_VS_PROTO_UDP=y
CONFIG_IP_VS_PROTO_ESP=y
CONFIG_IP_VS_PROTO_AH=y
CONFIG_IP_VS_RR=m
CONFIG_IP_VS_WRR=m
CONFIG_IP_VS_LC=m
CONFIG_IP_VS_WLC=m
CONFIG_IP_VS_LBLC=m
CONFIG_IP_VS_LBLCR=m
CONFIG_IP_VS_DH=m
CONFIG_IP_VS_SH=m
CONFIG_IP_VS_SED=m
CONFIG_IP_VS_NQ=m
CONFIG_IP_VS_FTP=m
CONFIG_IPV6=m
CONFIG_IPV6_PRIVACY=y
CONFIG_INET6_AH=m
CONFIG_INET6_ESP=m
CONFIG_INET6_IPCOMP=m
CONFIG_INET6_TUNNEL=m
CONFIG_IPV6_TUNNEL=m
CONFIG_NETFILTER=y
CONFIG_BRIDGE_NETFILTER=y
CONFIG_IP_NF_CONNTRACK=m
CONFIG_IP_NF_CONNTRACK_MARK=y
CONFIG_IP_NF_CT_PROTO_SCTP=m
CONFIG_IP_NF_FTP=m
CONFIG_IP_NF_IRC=m
CONFIG_IP_NF_TFTP=m
CONFIG_IP_NF_AMANDA=m
CONFIG_IP_NF_QUEUE=m
CONFIG_IP_NF_IPTABLES=m
CONFIG_IP_NF_MATCH_LIMIT=m
CONFIG_IP_NF_MATCH_IPRANGE=m
CONFIG_IP_NF_MATCH_MAC=m
CONFIG_IP_NF_MATCH_PKTTYPE=m
CONFIG_IP_NF_MATCH_MARK=m
CONFIG_IP_NF_MATCH_MULTIPORT=m
CONFIG_IP_NF_MATCH_TOS=m
CONFIG_IP_NF_MATCH_RECENT=m
CONFIG_IP_NF_MATCH_ECN=m
CONFIG_IP_NF_MATCH_DSCP=m
CONFIG_IP_NF_MATCH_AH_ESP=m
CONFIG_IP_NF_MATCH_LENGTH=m
CONFIG_IP_NF_MATCH_TTL=m
CONFIG_IP_NF_MATCH_TCPMSS=m
CONFIG_IP_NF_MATCH_HELPER=m
CONFIG_IP_NF_MATCH_STATE=m
CONFIG_IP_NF_MATCH_CONNTRACK=m
CONFIG_IP_NF_MATCH_OWNER=m
CONFIG_IP_NF_MATCH_PHYSDEV=m
CONFIG_IP_NF_MATCH_ADDRTYPE=m
CONFIG_IP_NF_MATCH_REALM=m
CONFIG_IP_NF_MATCH_SCTP=m
CONFIG_IP_NF_MATCH_COMMENT=m
CONFIG_IP_NF_MATCH_CONNMARK=m
CONFIG_IP_NF_MATCH_HASHLIMIT=m
CONFIG_IP_NF_FILTER=m
CONFIG_IP_NF_TARGET_REJECT=m
CONFIG_IP_NF_TARGET_LOG=m
CONFIG_IP_NF_TARGET_ULOG=m
CONFIG_IP_NF_TARGET_TCPMSS=m
CONFIG_IP_NF_NAT=m
CONFIG_IP_NF_NAT_NEEDED=y
CONFIG_IP_NF_TARGET_MASQUERADE=m
CONFIG_IP_NF_TARGET_REDIRECT=m
CONFIG_IP_NF_TARGET_NETMAP=m
CONFIG_IP_NF_TARGET_SAME=m
CONFIG_IP_NF_NAT_SNMP_BASIC=m
CONFIG_IP_NF_NAT_IRC=m
CONFIG_IP_NF_NAT_FTP=m
CONFIG_IP_NF_NAT_TFTP=m
CONFIG_IP_NF_NAT_AMANDA=m
CONFIG_IP_NF_MANGLE=m
CONFIG_IP_NF_TARGET_TOS=m
CONFIG_IP_NF_TARGET_ECN=m
CONFIG_IP_NF_TARGET_DSCP=m
CONFIG_IP_NF_TARGET_MARK=m
CONFIG_IP_NF_TARGET_CLASSIFY=m
CONFIG_IP_NF_TARGET_TTL=m
CONFIG_IP_NF_TARGET_CONNMARK=m
CONFIG_IP_NF_TARGET_CLUSTERIP=m
CONFIG_IP_NF_RAW=m
CONFIG_IP_NF_TARGET_NOTRACK=m
CONFIG_IP_NF_ARPTABLES=m
CONFIG_IP_NF_ARPFILTER=m
CONFIG_IP_NF_ARP_MANGLE=m
CONFIG_IP6_NF_QUEUE=m
CONFIG_IP6_NF_IPTABLES=m
CONFIG_IP6_NF_MATCH_LIMIT=m
CONFIG_IP6_NF_MATCH_MAC=m
CONFIG_IP6_NF_MATCH_RT=m
CONFIG_IP6_NF_MATCH_OPTS=m
CONFIG_IP6_NF_MATCH_FRAG=m
CONFIG_IP6_NF_MATCH_HL=m
CONFIG_IP6_NF_MATCH_MULTIPORT=m
CONFIG_IP6_NF_MATCH_OWNER=m
CONFIG_IP6_NF_MATCH_MARK=m
CONFIG_IP6_NF_MATCH_IPV6HEADER=m
CONFIG_IP6_NF_MATCH_AHESP=m
CONFIG_IP6_NF_MATCH_LENGTH=m
CONFIG_IP6_NF_MATCH_EUI64=m
CONFIG_IP6_NF_MATCH_PHYSDEV=m
CONFIG_IP6_NF_FILTER=m
CONFIG_IP6_NF_TARGET_LOG=m
CONFIG_IP6_NF_TARGET_REJECT=m
CONFIG_IP6_NF_MANGLE=m
CONFIG_IP6_NF_TARGET_MARK=m
CONFIG_IP6_NF_RAW=m
CONFIG_BRIDGE_NF_EBTABLES=m
CONFIG_BRIDGE_EBT_BROUTE=m
CONFIG_BRIDGE_EBT_T_FILTER=m
CONFIG_BRIDGE_EBT_T_NAT=m
CONFIG_BRIDGE_EBT_802_3=m
CONFIG_BRIDGE_EBT_AMONG=m
CONFIG_BRIDGE_EBT_ARP=m
CONFIG_BRIDGE_EBT_IP=m
CONFIG_BRIDGE_EBT_LIMIT=m
CONFIG_BRIDGE_EBT_MARK=m
CONFIG_BRIDGE_EBT_PKTTYPE=m
CONFIG_BRIDGE_EBT_STP=m
CONFIG_BRIDGE_EBT_VLAN=m
CONFIG_BRIDGE_EBT_ARPREPLY=m
CONFIG_BRIDGE_EBT_DNAT=m
CONFIG_BRIDGE_EBT_MARK_T=m
CONFIG_BRIDGE_EBT_REDIRECT=m
CONFIG_BRIDGE_EBT_SNAT=m
CONFIG_BRIDGE_EBT_LOG=m
CONFIG_BRIDGE_EBT_ULOG=m
CONFIG_IP_SCTP=m
CONFIG_SCTP_HMAC_MD5=y
CONFIG_ATM=m
CONFIG_ATM_CLIP=m
CONFIG_ATM_CLIP_NO_ICMP=y
CONFIG_ATM_LANE=m
CONFIG_ATM_MPOA=m
CONFIG_ATM_BR2684=m
CONFIG_BRIDGE=m
CONFIG_VLAN_8021Q=m
CONFIG_LLC=m
CONFIG_LLC2=m
CONFIG_IPX=m
CONFIG_ATALK=m
CONFIG_DEV_APPLETALK=y
CONFIG_IPDDP=m
CONFIG_IPDDP_ENCAP=y
CONFIG_IPDDP_DECAP=y
CONFIG_X25=m
CONFIG_LAPB=m
CONFIG_NET_SCHED=y
CONFIG_NET_SCH_CLK_GETTIMEOFDAY=y
CONFIG_NET_SCH_CBQ=m
CONFIG_NET_SCH_HTB=m
CONFIG_NET_SCH_HFSC=m
CONFIG_NET_SCH_ATM=m
CONFIG_NET_SCH_PRIO=m
CONFIG_NET_SCH_RED=m
CONFIG_NET_SCH_SFQ=m
CONFIG_NET_SCH_TEQL=m
CONFIG_NET_SCH_TBF=m
CONFIG_NET_SCH_GRED=m
CONFIG_NET_SCH_DSMARK=m
CONFIG_NET_SCH_NETEM=m
CONFIG_NET_SCH_INGRESS=m
CONFIG_NET_QOS=y
CONFIG_NET_ESTIMATOR=y
CONFIG_NET_CLS=y
CONFIG_NET_CLS_TCINDEX=m
CONFIG_NET_CLS_ROUTE4=m
CONFIG_NET_CLS_ROUTE=y
CONFIG_NET_CLS_FW=m
CONFIG_NET_CLS_U32=m
CONFIG_CLS_U32_PERF=y
CONFIG_CLS_U32_MARK=y
CONFIG_NET_CLS_RSVP=m
CONFIG_NET_CLS_RSVP6=m
CONFIG_NET_CLS_ACT=y
CONFIG_NET_ACT_POLICE=m
CONFIG_NET_ACT_GACT=m
CONFIG_GACT_PROB=y
CONFIG_NET_ACT_MIRRED=m
CONFIG_NET_ACT_IPT=m
CONFIG_NET_ACT_PEDIT=m
CONFIG_NET_PKTGEN=m
CONFIG_PREVENT_FIRMWARE_BUILD=y
CONFIG_FW_LOADER=y
CONFIG_PNP=y
CONFIG_PNPACPI=y
CONFIG_BLK_DEV_FD=y
CONFIG_BLK_DEV_LOOP=y
CONFIG_BLK_DEV_CRYPTOLOOP=m
CONFIG_BLK_DEV_NBD=m
CONFIG_BLK_DEV_RAM=y
CONFIG_BLK_DEV_RAM_COUNT=16
CONFIG_BLK_DEV_RAM_SIZE=64000
CONFIG_BLK_DEV_INITRD=y
CONFIG_LBD=y
CONFIG_CDROM_PKTCDVD=m
CONFIG_CDROM_PKTCDVD_BUFFERS=8
CONFIG_CDROM_PKTCDVD_WCACHE=y
CONFIG_IOSCHED_NOOP=y
CONFIG_IOSCHED_AS=y
CONFIG_IOSCHED_DEADLINE=y
CONFIG_IOSCHED_CFQ=y
CONFIG_ATA_OVER_ETH=m
CONFIG_IDE=y
CONFIG_BLK_DEV_IDE=y
CONFIG_BLK_DEV_IDEDISK=m
CONFIG_IDEDISK_MULTI_MODE=y
CONFIG_BLK_DEV_IDECD=y
CONFIG_BLK_DEV_IDESCSI=y
CONFIG_IDE_GENERIC=y
CONFIG_BLK_DEV_IDEPNP=y
CONFIG_BLK_DEV_IDEPCI=y
CONFIG_IDEPCI_SHARE_IRQ=y
CONFIG_BLK_DEV_OFFBOARD=y
CONFIG_BLK_DEV_GENERIC=y
CONFIG_BLK_DEV_IDEDMA_PCI=y
CONFIG_IDEDMA_PCI_AUTO=y
CONFIG_BLK_DEV_AEC62XX=m
CONFIG_BLK_DEV_ALI15X3=m
CONFIG_BLK_DEV_AMD74XX=m
CONFIG_BLK_DEV_ATIIXP=m
CONFIG_BLK_DEV_CMD64X=m
CONFIG_BLK_DEV_TRIFLEX=m
CONFIG_BLK_DEV_CY82C693=m
CONFIG_BLK_DEV_CS5520=m
CONFIG_BLK_DEV_CS5530=m
CONFIG_BLK_DEV_HPT34X=m
CONFIG_HPT34X_AUTODMA=y
CONFIG_BLK_DEV_HPT366=m
CONFIG_BLK_DEV_SC1200=m
CONFIG_BLK_DEV_PIIX=y
CONFIG_BLK_DEV_NS87415=m
CONFIG_BLK_DEV_SVWKS=m
CONFIG_BLK_DEV_SIIMAGE=m
CONFIG_BLK_DEV_SIS5513=m
CONFIG_BLK_DEV_SLC90E66=m
CONFIG_BLK_DEV_TRM290=m
CONFIG_BLK_DEV_VIA82CXXX=m
CONFIG_BLK_DEV_IDEDMA=y
CONFIG_IDEDMA_AUTO=y
CONFIG_SCSI=y
CONFIG_SCSI_PROC_FS=y
CONFIG_BLK_DEV_SD=y
CONFIG_CHR_DEV_ST=y
CONFIG_BLK_DEV_SR=y
CONFIG_CHR_DEV_SG=y
CONFIG_CHR_DEV_SCH=m
CONFIG_SCSI_MULTI_LUN=y
CONFIG_SCSI_CONSTANTS=y
CONFIG_SCSI_LOGGING=y
CONFIG_SCSI_SPI_ATTRS=y
CONFIG_SCSI_FC_ATTRS=m
CONFIG_SCSI_ISCSI_ATTRS=m
CONFIG_SCSI_AIC7XXX=m
CONFIG_AIC7XXX_CMDS_PER_DEVICE=32
CONFIG_AIC7XXX_RESET_DELAY_MS=5000
CONFIG_AIC7XXX_DEBUG_MASK=0
CONFIG_AIC7XXX_REG_PRETTY_PRINT=y
CONFIG_MEGARAID_NEWGEN=y
CONFIG_MEGARAID_MM=y
CONFIG_MEGARAID_MAILBOX=y
CONFIG_SCSI_QLA2XXX=y
CONFIG_SCSI_DEBUG=m
CONFIG_I2O=m
CONFIG_I2O_EXT_ADAPTEC=y
CONFIG_I2O_EXT_ADAPTEC_DMA64=y
CONFIG_I2O_CONFIG=m
CONFIG_I2O_CONFIG_OLD_IOCTL=y
CONFIG_I2O_BLOCK=m
CONFIG_I2O_SCSI=m
CONFIG_I2O_PROC=m
CONFIG_NETDEVICES=y
CONFIG_DUMMY=m
CONFIG_BONDING=m
CONFIG_EQUALIZER=m
CONFIG_TUN=m
CONFIG_MII=m
CONFIG_E1000=y
CONFIG_E1000_NAPI=y
CONFIG_PPP=m
CONFIG_PPP_MULTILINK=y
CONFIG_PPP_FILTER=y
CONFIG_PPP_ASYNC=m
CONFIG_PPP_SYNC_TTY=m
CONFIG_PPP_DEFLATE=m
CONFIG_PPP_BSDCOMP=m
CONFIG_PPPOE=m
CONFIG_PPPOATM=m
CONFIG_SLIP=m
CONFIG_SLIP_COMPRESSED=y
CONFIG_SLIP_SMART=y
CONFIG_SLIP_MODE_SLIP6=y
CONFIG_SHAPER=m
CONFIG_NETCONSOLE=m
CONFIG_NETPOLL=y
CONFIG_NETPOLL_RX=y
CONFIG_NETPOLL_TRAP=y
CONFIG_NET_POLL_CONTROLLER=y
CONFIG_INPUT=y
CONFIG_INPUT_MOUSEDEV=y
CONFIG_INPUT_MOUSEDEV_PSAUX=y
CONFIG_INPUT_MOUSEDEV_SCREEN_X=1024
CONFIG_INPUT_MOUSEDEV_SCREEN_Y=768
CONFIG_INPUT_JOYDEV=m
CONFIG_INPUT_TSDEV=m
CONFIG_INPUT_TSDEV_SCREEN_X=240
CONFIG_INPUT_TSDEV_SCREEN_Y=320
CONFIG_INPUT_EVDEV=m
CONFIG_INPUT_KEYBOARD=y
CONFIG_KEYBOARD_ATKBD=y
CONFIG_KEYBOARD_SUNKBD=m
CONFIG_KEYBOARD_XTKBD=m
CONFIG_KEYBOARD_NEWTON=m
CONFIG_INPUT_MOUSE=y
CONFIG_MOUSE_PS2=y
CONFIG_MOUSE_SERIAL=m
CONFIG_INPUT_JOYSTICK=y
CONFIG_JOYSTICK_ANALOG=m
CONFIG_JOYSTICK_A3D=m
CONFIG_JOYSTICK_ADI=m
CONFIG_JOYSTICK_COBRA=m
CONFIG_JOYSTICK_GF2K=m
CONFIG_JOYSTICK_GRIP=m
CONFIG_JOYSTICK_GRIP_MP=m
CONFIG_JOYSTICK_GUILLEMOT=m
CONFIG_JOYSTICK_INTERACT=m
CONFIG_JOYSTICK_SIDEWINDER=m
CONFIG_JOYSTICK_TMDC=m
CONFIG_JOYSTICK_IFORCE=m
CONFIG_JOYSTICK_IFORCE_USB=y
CONFIG_JOYSTICK_IFORCE_232=y
CONFIG_JOYSTICK_WARRIOR=m
CONFIG_JOYSTICK_MAGELLAN=m
CONFIG_JOYSTICK_SPACEORB=m
CONFIG_JOYSTICK_SPACEBALL=m
CONFIG_JOYSTICK_STINGER=m
CONFIG_JOYSTICK_TWIDJOY=m
CONFIG_JOYSTICK_JOYDUMP=m
CONFIG_INPUT_TOUCHSCREEN=y
CONFIG_TOUCHSCREEN_GUNZE=m
CONFIG_TOUCHSCREEN_ELO=m
CONFIG_TOUCHSCREEN_MK712=m
CONFIG_INPUT_MISC=y
CONFIG_INPUT_PCSPKR=y
CONFIG_INPUT_UINPUT=m
CONFIG_SERIO=y
CONFIG_SERIO_I8042=y
CONFIG_SERIO_SERPORT=m
CONFIG_SERIO_CT82C710=m
CONFIG_SERIO_PCIPS2=m
CONFIG_SERIO_LIBPS2=y
CONFIG_SERIO_RAW=m
CONFIG_GAMEPORT=m
CONFIG_GAMEPORT_NS558=m
CONFIG_GAMEPORT_L4=m
CONFIG_GAMEPORT_EMU10K1=m
CONFIG_GAMEPORT_FM801=m
CONFIG_VT=y
CONFIG_VT_CONSOLE=y
CONFIG_HW_CONSOLE=y
CONFIG_SERIAL_8250=y
CONFIG_SERIAL_8250_CONSOLE=y
CONFIG_SERIAL_8250_NR_UARTS=4
CONFIG_SERIAL_CORE=y
CONFIG_SERIAL_CORE_CONSOLE=y
CONFIG_UNIX98_PTYS=y
CONFIG_LEGACY_PTYS=y
CONFIG_LEGACY_PTY_COUNT=256
CONFIG_IPMI_HANDLER=m
CONFIG_IPMI_PANIC_EVENT=y
CONFIG_IPMI_PANIC_STRING=y
CONFIG_IPMI_DEVICE_INTERFACE=m
CONFIG_IPMI_SI=m
CONFIG_IPMI_WATCHDOG=m
CONFIG_IPMI_POWEROFF=m
CONFIG_WATCHDOG=y
CONFIG_SOFT_WATCHDOG=m
CONFIG_ACQUIRE_WDT=m
CONFIG_ADVANTECH_WDT=m
CONFIG_ALIM1535_WDT=m
CONFIG_ALIM7101_WDT=m
CONFIG_SC520_WDT=m
CONFIG_EUROTECH_WDT=m
CONFIG_IB700_WDT=m
CONFIG_WAFER_WDT=m
CONFIG_I8XX_TCO=m
CONFIG_SC1200_WDT=m
CONFIG_60XX_WDT=m
CONFIG_CPU5_WDT=m
CONFIG_W83627HF_WDT=m
CONFIG_W83877F_WDT=m
CONFIG_MACHZ_WDT=m
CONFIG_PCIPCWATCHDOG=m
CONFIG_WDTPCI=m
CONFIG_WDT_501_PCI=y
CONFIG_USBPCWATCHDOG=m
CONFIG_HW_RANDOM=m
CONFIG_NVRAM=m
CONFIG_RTC=y
CONFIG_DTLK=m
CONFIG_AGP=m
CONFIG_AGP_INTEL=m
CONFIG_DRM=m
CONFIG_DRM_R128=m
CONFIG_DRM_RADEON=m
CONFIG_DRM_I810=m
CONFIG_DRM_I830=m
CONFIG_DRM_I915=m
CONFIG_RAW_DRIVER=m
CONFIG_HPET=y
CONFIG_HPET_MMAP=y
CONFIG_MAX_RAW_DEVS=4096
CONFIG_HANGCHECK_TIMER=m
CONFIG_I2C=m
CONFIG_I2C_CHARDEV=m
CONFIG_I2C_ALGOBIT=m
CONFIG_I2C_ALGOPCF=m
CONFIG_I2C_ALGOPCA=m
CONFIG_I2C_ALI1535=m
CONFIG_I2C_ALI1563=m
CONFIG_I2C_ALI15X3=m
CONFIG_I2C_AMD756=m
CONFIG_I2C_AMD756_S4882=m
CONFIG_I2C_AMD8111=m
CONFIG_I2C_I801=m
CONFIG_I2C_I810=m
CONFIG_I2C_PIIX4=m
CONFIG_I2C_NFORCE2=m
CONFIG_I2C_PARPORT_LIGHT=m
CONFIG_I2C_PROSAVAGE=m
CONFIG_I2C_SAVAGE4=m
CONFIG_SCx200_ACB=m
CONFIG_I2C_SIS5595=m
CONFIG_I2C_SIS630=m
CONFIG_I2C_SIS96X=m
CONFIG_I2C_STUB=m
CONFIG_I2C_VIA=m
CONFIG_I2C_VIAPRO=m
CONFIG_I2C_VOODOO3=m
CONFIG_I2C_PCA_ISA=m
CONFIG_SENSORS_EEPROM=m
CONFIG_SENSORS_PCF8574=m
CONFIG_SENSORS_PCF8591=m
CONFIG_SENSORS_RTC8564=m
CONFIG_VIDEO_SELECT=y
CONFIG_VGA_CONSOLE=y
CONFIG_DUMMY_CONSOLE=y
CONFIG_USB_ARCH_HAS_HCD=y
CONFIG_USB_ARCH_HAS_OHCI=y
CONFIG_USB=m
CONFIG_USB_DEVICEFS=y
CONFIG_USB_EHCI_HCD=m
CONFIG_USB_EHCI_SPLIT_ISO=y
CONFIG_USB_EHCI_ROOT_HUB_TT=y
CONFIG_USB_OHCI_HCD=m
CONFIG_USB_OHCI_LITTLE_ENDIAN=y
CONFIG_USB_UHCI_HCD=m
CONFIG_USB_SL811_HCD=m
CONFIG_USB_ACM=m
CONFIG_USB_PRINTER=m
CONFIG_USB_STORAGE=m
CONFIG_USB_STORAGE_DATAFAB=y
CONFIG_USB_STORAGE_FREECOM=y
CONFIG_USB_STORAGE_ISD200=y
CONFIG_USB_STORAGE_DPCM=y
CONFIG_USB_STORAGE_SDDR09=y
CONFIG_USB_STORAGE_SDDR55=y
CONFIG_USB_STORAGE_JUMPSHOT=y
CONFIG_USB_HID=m
CONFIG_USB_HIDINPUT=y
CONFIG_HID_FF=y
CONFIG_HID_PID=y
CONFIG_LOGITECH_FF=y
CONFIG_THRUSTMASTER_FF=y
CONFIG_USB_HIDDEV=y
CONFIG_USB_AIPTEK=m
CONFIG_USB_WACOM=m
CONFIG_USB_KBTAB=m
CONFIG_USB_POWERMATE=m
CONFIG_USB_MTOUCH=m
CONFIG_USB_EGALAX=m
CONFIG_USB_XPAD=m
CONFIG_USB_ATI_REMOTE=m
CONFIG_USB_MDC800=m
CONFIG_USB_MICROTEK=m
CONFIG_USB_DABUSB=m
CONFIG_USB_CATC=m
CONFIG_USB_KAWETH=m
CONFIG_USB_PEGASUS=m
CONFIG_USB_RTL8150=m
CONFIG_USB_USBNET=m
CONFIG_USB_NET_CDCETHER=m
CONFIG_USB_MON=y
CONFIG_USB_SERIAL=m
CONFIG_USB_SERIAL_GENERIC=y
CONFIG_USB_SERIAL_BELKIN=m
CONFIG_USB_SERIAL_DIGI_ACCELEPORT=m
CONFIG_USB_SERIAL_CYPRESS_M8=m
CONFIG_USB_SERIAL_EMPEG=m
CONFIG_USB_SERIAL_FTDI_SIO=m
CONFIG_USB_SERIAL_VISOR=m
CONFIG_USB_SERIAL_IPAQ=m
CONFIG_USB_SERIAL_IR=m
CONFIG_USB_SERIAL_EDGEPORT=m
CONFIG_USB_SERIAL_EDGEPORT_TI=m
CONFIG_USB_SERIAL_GARMIN=m
CONFIG_USB_SERIAL_IPW=m
CONFIG_USB_SERIAL_KEYSPAN_PDA=m
CONFIG_USB_SERIAL_KEYSPAN=m
CONFIG_USB_SERIAL_KEYSPAN_MPR=y
CONFIG_USB_SERIAL_KEYSPAN_USA28=y
CONFIG_USB_SERIAL_KEYSPAN_USA28X=y
CONFIG_USB_SERIAL_KEYSPAN_USA28XA=y
CONFIG_USB_SERIAL_KEYSPAN_USA28XB=y
CONFIG_USB_SERIAL_KEYSPAN_USA19=y
CONFIG_USB_SERIAL_KEYSPAN_USA18X=y
CONFIG_USB_SERIAL_KEYSPAN_USA19W=y
CONFIG_USB_SERIAL_KEYSPAN_USA19QW=y
CONFIG_USB_SERIAL_KEYSPAN_USA19QI=y
CONFIG_USB_SERIAL_KEYSPAN_USA49W=y
CONFIG_USB_SERIAL_KEYSPAN_USA49WLC=y
CONFIG_USB_SERIAL_KLSI=m
CONFIG_USB_SERIAL_KOBIL_SCT=m
CONFIG_USB_SERIAL_MCT_U232=m
CONFIG_USB_SERIAL_PL2303=m
CONFIG_USB_SERIAL_SAFE=m
CONFIG_USB_SERIAL_SAFE_PADDED=y
CONFIG_USB_SERIAL_TI=m
CONFIG_USB_SERIAL_CYBERJACK=m
CONFIG_USB_SERIAL_XIRCOM=m
CONFIG_USB_SERIAL_OMNINET=m
CONFIG_USB_EZUSB=y
CONFIG_USB_EMI62=m
CONFIG_USB_EMI26=m
CONFIG_USB_AUERSWALD=m
CONFIG_USB_RIO500=m
CONFIG_USB_LEGOTOWER=m
CONFIG_USB_LCD=m
CONFIG_USB_LED=m
CONFIG_USB_CYTHERM=m
CONFIG_USB_PHIDGETKIT=m
CONFIG_USB_PHIDGETSERVO=m
CONFIG_USB_IDMOUSE=m
CONFIG_USB_SISUSBVGA=m
CONFIG_USB_ATM=m
CONFIG_USB_SPEEDTOUCH=m
CONFIG_MMC=m
CONFIG_MMC_BLOCK=m
CONFIG_EXT2_FS=y
CONFIG_EXT2_FS_XATTR=y
CONFIG_EXT2_FS_POSIX_ACL=y
CONFIG_EXT2_FS_SECURITY=y
CONFIG_EXT3_FS=m
CONFIG_EXT3_FS_XATTR=y
CONFIG_EXT3_FS_POSIX_ACL=y
CONFIG_EXT3_FS_SECURITY=y
CONFIG_JBD=m
CONFIG_JBD_DEBUG=y
CONFIG_FS_MBCACHE=y
CONFIG_REISERFS_FS=y
CONFIG_REISERFS_FS_XATTR=y
CONFIG_REISERFS_FS_POSIX_ACL=y
CONFIG_REISERFS_FS_SECURITY=y
CONFIG_JFS_FS=m
CONFIG_JFS_POSIX_ACL=y
CONFIG_JFS_SECURITY=y
CONFIG_JFS_STATISTICS=y
CONFIG_FS_POSIX_ACL=y
CONFIG_XFS_FS=m
CONFIG_XFS_QUOTA=m
CONFIG_XFS_SECURITY=y
CONFIG_XFS_POSIX_ACL=y
CONFIG_XFS_RT=y
CONFIG_ROMFS_FS=m
CONFIG_INOTIFY=y
CONFIG_QUOTACTL=y
CONFIG_DNOTIFY=y
CONFIG_AUTOFS_FS=m
CONFIG_AUTOFS4_FS=m
CONFIG_ISO9660_FS=y
CONFIG_JOLIET=y
CONFIG_ZISOFS=y
CONFIG_ZISOFS_FS=y
CONFIG_UDF_FS=m
CONFIG_UDF_NLS=y
CONFIG_FAT_FS=m
CONFIG_MSDOS_FS=m
CONFIG_VFAT_FS=m
CONFIG_FAT_DEFAULT_CODEPAGE=437
CONFIG_FAT_DEFAULT_IOCHARSET="iso8859-1"
CONFIG_NTFS_FS=m
CONFIG_NTFS_RW=y
CONFIG_PROC_FS=y
CONFIG_PROC_KCORE=y
CONFIG_SYSFS=y
CONFIG_TMPFS=y
CONFIG_HUGETLBFS=y
CONFIG_HUGETLB_PAGE=y
CONFIG_RAMFS=y
CONFIG_UFS_FS=m
CONFIG_SMB_FS=m
CONFIG_SMB_NLS_DEFAULT=y
CONFIG_SMB_NLS_REMOTE="cp850"
CONFIG_CIFS=m
CONFIG_CIFS_STATS=y
CONFIG_CIFS_XATTR=y
CONFIG_CIFS_POSIX=y
CONFIG_MSDOS_PARTITION=y
CONFIG_NLS=y
CONFIG_NLS_DEFAULT="utf8"
CONFIG_NLS_CODEPAGE_437=m
CONFIG_NLS_CODEPAGE_737=m
CONFIG_NLS_CODEPAGE_775=m
CONFIG_NLS_CODEPAGE_850=m
CONFIG_NLS_CODEPAGE_852=m
CONFIG_NLS_CODEPAGE_855=m
CONFIG_NLS_CODEPAGE_857=m
CONFIG_NLS_CODEPAGE_860=m
CONFIG_NLS_CODEPAGE_861=m
CONFIG_NLS_CODEPAGE_862=m
CONFIG_NLS_CODEPAGE_863=m
CONFIG_NLS_CODEPAGE_864=m
CONFIG_NLS_CODEPAGE_865=m
CONFIG_NLS_CODEPAGE_866=m
CONFIG_NLS_CODEPAGE_869=m
CONFIG_NLS_CODEPAGE_936=m
CONFIG_NLS_CODEPAGE_950=m
CONFIG_NLS_CODEPAGE_932=m
CONFIG_NLS_CODEPAGE_949=m
CONFIG_NLS_CODEPAGE_874=m
CONFIG_NLS_ISO8859_8=m
CONFIG_NLS_CODEPAGE_1250=m
CONFIG_NLS_CODEPAGE_1251=m
CONFIG_NLS_ASCII=m
CONFIG_NLS_ISO8859_1=m
CONFIG_NLS_ISO8859_2=m
CONFIG_NLS_ISO8859_3=m
CONFIG_NLS_ISO8859_4=m
CONFIG_NLS_ISO8859_5=m
CONFIG_NLS_ISO8859_6=m
CONFIG_NLS_ISO8859_7=m
CONFIG_NLS_ISO8859_9=m
CONFIG_NLS_ISO8859_13=m
CONFIG_NLS_ISO8859_14=m
CONFIG_NLS_ISO8859_15=m
CONFIG_NLS_KOI8_R=m
CONFIG_NLS_KOI8_U=m
CONFIG_NLS_UTF8=m
CONFIG_PROFILING=y
CONFIG_OPROFILE=m
CONFIG_DEBUG_KERNEL=y
CONFIG_MAGIC_SYSRQ=y
CONFIG_LOG_BUF_SHIFT=17
CONFIG_DEBUG_BUGVERBOSE=y
CONFIG_EARLY_PRINTK=y
CONFIG_DEBUG_STACKOVERFLOW=y
CONFIG_X86_FIND_SMP_CONFIG=y
CONFIG_X86_MPPARSE=y
CONFIG_CRYPTO=y
CONFIG_CRYPTO_HMAC=y
CONFIG_CRYPTO_NULL=m
CONFIG_CRYPTO_MD4=m
CONFIG_CRYPTO_MD5=y
CONFIG_CRYPTO_SHA1=m
CONFIG_CRYPTO_SHA256=m
CONFIG_CRYPTO_SHA512=m
CONFIG_CRYPTO_WP512=m
CONFIG_CRYPTO_DES=y
CONFIG_CRYPTO_BLOWFISH=m
CONFIG_CRYPTO_TWOFISH=m
CONFIG_CRYPTO_SERPENT=m
CONFIG_CRYPTO_AES_586=m
CONFIG_CRYPTO_CAST5=m
CONFIG_CRYPTO_CAST6=m
CONFIG_CRYPTO_TEA=m
CONFIG_CRYPTO_ARC4=m
CONFIG_CRYPTO_KHAZAD=m
CONFIG_CRYPTO_ANUBIS=m
CONFIG_CRYPTO_DEFLATE=m
CONFIG_CRYPTO_MICHAEL_MIC=m
CONFIG_CRYPTO_CRC32C=m
CONFIG_CRYPTO_TEST=m
CONFIG_CRC_CCITT=m
CONFIG_CRC16=m
CONFIG_CRC32=y
CONFIG_LIBCRC32C=m
CONFIG_ZLIB_INFLATE=y
CONFIG_ZLIB_DEFLATE=m
CONFIG_GENERIC_HARDIRQS=y
CONFIG_GENERIC_IRQ_PROBE=y
CONFIG_GENERIC_PENDING_IRQ=y
CONFIG_X86_SMP=y
CONFIG_X86_HT=y
CONFIG_X86_BIOS_REBOOT=y
CONFIG_X86_TRAMPOLINE=y
CONFIG_PC=y
On Wed, 14 Sep 2005, Denis Vlasenko wrote:
> > It's documented as being suboptimal to use inc/dec due to it modifying all
> > of eflags resulting in dependency related stalls. add/sub only modifies
> > one bit of eflags so is more optimal. However there is a problem of
>
> ?! add/sub doesn't modify "only one bit in eflags", it modifies all.
> In fact, it's dec/inc which does not modify all bits.
> It doesn't touch 'carry' bit (IIRC).
>
> If inc/dec is slower on P4, it must be just another P4 quirk.
You're right about the add and the number of modified bits. The documented
part is found in the P4 optimisation manual;
"The inc and dec instructions should always be avoided. Using add
and sub instructions instead avoids data dependence and improves
performance."
-- 2-12 IA-32 Intel Architecture Optimization Reference Manual
At 09:59 14.09.2005 +0300, Denis Vlasenko wrote:
>On Wednesday 14 September 2005 09:48, Zwane Mwaikambo wrote:
> > On Wed, 14 Sep 2005, Chris White wrote:
> >
> > > That's correct, gcc 3.4 started the -mtune flag. Chances are if you
> really
> > > want the -mtune optimizations you're going to have to upgrade to gcc
> 3.4 or
> > > greater.
> > >
> > > > This, of course, heavily penalizes P4's (the notorious inc/dec).
> > >
> > > Are you referring to cpu cycle counts? Is there certain code that
> causes the
> > > kernel to perform that unfavorably by a large scale?
> >
> > It's documented as being suboptimal to use inc/dec due to it modifying all
> > of eflags resulting in dependency related stalls. add/sub only modifies
> > one bit of eflags so is more optimal. However there is a problem of
>
>?! add/sub doesn't modify "only one bit in eflags", it modifies all.
>In fact, it's dec/inc which does not modify all bits.
>It doesn't touch 'carry' bit (IIRC).
>
>If inc/dec is slower on P4, it must be just another P4 quirk.
>
> > increased code size with add/sub.
> >
> > But i've never benchmarked all of this ;)
>
>I don't even have one to test this.
In the Intel Architecture Optimization document it specifically states
(Chapter 2.6) :
"Avoid instructions that unnecessarily introduce dependence-related
stalls: inc and dec instructions, .....".
And again on page 2-11 :
"The inc and dec instructions should always be avoided. Using add and
sub instructions instead avoids data dependence and improves performance".
And on page 2-71 :
"The inc and dec instructions modify only a subset of flags in the flag
register.
This creates a dependence on all previous writes of the flag register.
This is especially problematic when these instructions are on the critical
path because they are used to change an address for a load on which
many other instructions depend. "
However, the kernel include and arch have a liberal sprinkling of inc/dec,
and AFAICT some of these in hot-path.
Margit
> > > It's documented as being suboptimal to use inc/dec due to it modifying all
> > > of eflags resulting in dependency related stalls. add/sub only modifies
> > > one bit of eflags so is more optimal. However there is a problem of
> >
> > ?! add/sub doesn't modify "only one bit in eflags", it modifies all.
> > In fact, it's dec/inc which does not modify all bits.
> > It doesn't touch 'carry' bit (IIRC).
> >
> > If inc/dec is slower on P4, it must be just another P4 quirk.
>
> You're right about the add and the number of modified bits. The documented
> part is found in the P4 optimisation manual;
>
> "The inc and dec instructions should always be avoided. Using add
> and sub instructions instead avoids data dependence and improves
> performance."
I read this as "get saner processor".
But frankly any CPU optimization manuals, not just Intel's,
go to semi-absurd suggestions like "align all data
and branch targets to $BIGNUM bytes", "do not use instruction X
(because we failed to make it work reasonably fast), use Y".
Of course next gen CPU will prefer Y over X
(for example, AMD's recomended way to do NOPs).
--
vda
>
> In the Intel Architecture Optimization document it specifically states
> (Chapter 2.6) :
> "Avoid instructions that unnecessarily introduce dependence-related
> stalls: inc and dec instructions, .....".
> And again on page 2-11 :
> "The inc and dec instructions should always be avoided. Using add and
> sub instructions instead avoids data dependence and improves performance".
> And on page 2-71 :
> "The inc and dec instructions modify only a subset of flags in the flag
> register.
> This creates a dependence on all previous writes of the flag register.
> This is especially problematic when these instructions are on the critical
> path because they are used to change an address for a load on which
> many other instructions depend. "
Well it sounds dramatic but in reality I doubt it is such a big deal.
Anyone to bench it?
> However, the kernel include and arch have a liberal sprinkling of inc/dec,
> and AFAICT some of these in hot-path.
--
vda