> > From: Ravi Kerur [mailto:rkerur at gmail.com] > Sent: Tuesday, December 16, 2014 8:14 PM > To: Ananyev, Konstantin > Cc: Neil Horman; dev at dpdk.org > Subject: Re: [dpdk-dev] [PATCH] Minor fixes in rte_common.h file. > > > > On Tue, Dec 16, 2014 at 9:23 AM, Ananyev, Konstantin <konstantin.ananyev at > intel.com> wrote: > > > > -----Original Message----- > > From: dev [mailto:dev-bounces at dpdk.org] On Behalf Of Ravi Kerur > > Sent: Tuesday, December 16, 2014 4:47 PM > > To: Neil Horman > > Cc: dev at dpdk.org > > Subject: Re: [dpdk-dev] [PATCH] Minor fixes in rte_common.h file. > > > > On Sat, Dec 13, 2014 at 2:39 AM, Neil Horman <nhorman at tuxdriver.com> > > wrote: > > > > > > On Fri, Dec 12, 2014 at 03:04:34PM -0800, r k wrote: > > > > Subject: [PATCH] Minor fixes in rte_common.h file. > > > > > > > > Fix rte_is_power_of_2 since 0 is not. > > > > Avoid branching instructions in RTE_MAX and RTE_MIN. > > > > > > > > Signed-off-by: Ravi Kerur <rkerur at gmail.com> > > > > --- > > > >? lib/librte_eal/common/include/rte_common.h | 6 +++--- > > > >? lib/librte_pmd_e1000/igb_pf.c? ? ? ? ? ? ? | 4 ++-- > > > >? lib/librte_pmd_ixgbe/ixgbe_pf.c? ? ? ? ? ? | 4 ++-- > > > >? 3 files changed, 7 insertions(+), 7 deletions(-) > > > > > > > > diff --git a/lib/librte_eal/common/include/rte_common.h > > > > b/lib/librte_eal/common/include/rte_common.h > > > > index 921b91f..e163f35 100644 > > > > --- a/lib/librte_eal/common/include/rte_common.h > > > > +++ b/lib/librte_eal/common/include/rte_common.h > > > > @@ -203,7 +203,7 @@ extern int RTE_BUILD_BUG_ON_detected_error;? static > > > > inline int? rte_is_power_of_2(uint32_t n)? { > > > > -? ? ? ?return ((n-1) & n) == 0; > > > > +? ? ? ?return n && !(n & (n - 1)); > > > >? } > > > > > > > >? /** > > > > @@ -259,7 +259,7 @@ rte_align64pow2(uint64_t v)? #define RTE_MIN(a, b) > > > ({ \ > > > >? ? ? ? ? ? ? ? ?typeof (a) _a = (a); \ > > > >? ? ? ? ? ? ? ? ?typeof (b) _b = (b); \ > > > > -? ? ? ? ? ? ? ?_a < _b ? _a : _b; \ > > > > +? ? ? ? ? ? ? ? _b ^ ((_a ^ _b) & -(_a < _b)); \ > > > Are you sure this is actually faster than the branch version?? What about > > > using > > > a cmov instead? > > > > > > > > <rk> i am pretty sure modified code is faster than branching. I remember > > cmov had performance issues esp. on Pentuim-4 not sure how new intel cpu's > > perform. > I also think most modern compilers are smart enough to avoid any branching > here and will use cmov instead. > And we are way ahead of Pentium 4 times these days. > Konstantin > > <rk>Konstantin, ?Can you please elaborate, is it something done automatically > with Intel's icc compiler? My understanding is branch > prediction can be influenced only by using compiler builtin i.e. > __builtin_expect() , without this compiler will generate regular > instructions(cmp/jump instructions). I wrote small program and compiled with > gcc -02/-03, don't see cmov instruction.
I am saying that there is probably no need to modify these macros. On IA , for constructions like: "_a < _b ? _a : _b;" modern compilers in many cases will avoid any branches and emit cmov instead. $ cat tcmv1.c #include <stdint.h> #include <stddef.h> #define RTE_MIN(a, b) ({ \ typeof (a) _a = (a); \ typeof (b) _b = (b); \ _a < _b ? _a : _b; \ }) int fxmini32(int a, int b) { return RTE_MIN(a, b); } int fxminu64(uint64_t a, uint64_t b) { return RTE_MIN(a, b); } $gcc -O3 -m64 -S tcmv1.c $ cat tcmv1.s .file "tcmv1.c" .text .p2align 4,,15 .globl fxmini32 .type fxmini32, @function fxmini32: .LFB0: .cfi_startproc cmpl %esi, %edi movl %esi, %eax cmovle %edi, %eax ret .cfi_endproc .LFE0: .size fxmini32, .-fxmini32 .p2align 4,,15 .globl fxminu64 .type fxminu64, @function fxminu64: .LFB1: .cfi_startproc cmpq %rsi, %rdi movq %rsi, %rax cmovbe %rdi, %rax ret .cfi_endproc gcc version 4.8.3 clang produces similar code. Konstantin > > > > > >? ? ? ? ?}) > > > > > > > >? /** > > > > @@ -268,7 +268,7 @@ rte_align64pow2(uint64_t v)? #define RTE_MAX(a, b) > > > ({ \ > > > >? ? ? ? ? ? ? ? ?typeof (a) _a = (a); \ > > > >? ? ? ? ? ? ? ? ?typeof (b) _b = (b); \ > > > > -? ? ? ? ? ? ? ?_a > _b ? _a : _b; \ > > > > +? ? ? ? ? ? ? ?_a ^ ((_a ^ _b) & -(_a < _b)); \ > > > Same as above > > > > > > <rk> Same as above. > > > > > >? ? ? ? ?}) > > > > > > > >? /*********** Other general functions / macros ********/ diff --git > > > > a/lib/librte_pmd_e1000/igb_pf.c b/lib/librte_pmd_e1000/igb_pf.c index > > > > bc3816a..546499c 100644 > > > > --- a/lib/librte_pmd_e1000/igb_pf.c > > > > +++ b/lib/librte_pmd_e1000/igb_pf.c > > > > @@ -321,11 +321,11 @@ igb_vf_set_mac_addr(struct rte_eth_dev *dev, > > > uint32_t > > > > vf, uint32_t *msgbuf)? static int? igb_vf_set_multicast(struct > > > rte_eth_dev > > > > *dev, __rte_unused uint32_t vf, uint32_t *msgbuf)? { > > > > -? ? ? ?int i; > > > > +? ? ? ?int16_t i; > > > >? ? ? ? ?uint32_t vector_bit; > > > >? ? ? ? ?uint32_t vector_reg; > > > >? ? ? ? ?uint32_t mta_reg; > > > > -? ? ? ?int entries = (msgbuf[0] & E1000_VT_MSGINFO_MASK) >> > > > > +? ? ? ?int32_t entries = (msgbuf[0] & E1000_VT_MSGINFO_MASK) >> > > > >? ? ? ? ? ? ? ? ?E1000_VT_MSGINFO_SHIFT; > > > NAK, this has nothing to do with the included changelog > > > > > > > <rk> It does, it causes compilation errors such as > > > > /root/dpdk-new/dpdk/lib/librte_pmd_e1000/igb_pf.c: In function > > \u2018igb_pf_mbx_process\u2019: > > /root/dpdk-new/dpdk/lib/librte_pmd_e1000/igb_pf.c:350:23: error: array > > subscript is above array bounds [-Werror=array-bounds] > >? ? vfinfo->vf_mc_hashes[i] = hash_list[i]; > >? ? ? ? ? ? ? ? ? ? ? ? ^ > > cc1: all warnings being treated as errors > > > > Also it is always better to use explicit int definitions esp. for 64bit > > systems. > > > > > > > > > > > > >? ? ? ? ?uint16_t *hash_list = (uint16_t *)&msgbuf[1]; > > > >? ? ? ? ?struct e1000_hw *hw = > > > > E1000_DEV_PRIVATE_TO_HW(dev->data->dev_private); > > > > diff --git a/lib/librte_pmd_ixgbe/ixgbe_pf.c > > > > b/lib/librte_pmd_ixgbe/ixgbe_pf.c index 51da1fd..426caf9 100644 > > > > --- a/lib/librte_pmd_ixgbe/ixgbe_pf.c > > > > +++ b/lib/librte_pmd_ixgbe/ixgbe_pf.c > > > > @@ -390,7 +390,7 @@ ixgbe_vf_set_multicast(struct rte_eth_dev *dev, > > > > __rte_unused uint32_t vf, uint32 > > > >? ? ? ? ?struct ixgbe_hw *hw = > > > > IXGBE_DEV_PRIVATE_TO_HW(dev->data->dev_private); > > > >? ? ? ? ?struct ixgbe_vf_info *vfinfo = > > > >? ? ? ? ? ? ? ? > > > >?*(IXGBE_DEV_PRIVATE_TO_P_VFDATA(dev->data->dev_private)); > > > > -? ? ? ?int nb_entries = (msgbuf[0] & IXGBE_VT_MSGINFO_MASK) >> > > > > +? ? ? ?int32_t nb_entries = (msgbuf[0] & IXGBE_VT_MSGINFO_MASK) >> > > > >? ? ? ? ? ? ? ? ?IXGBE_VT_MSGINFO_SHIFT; > > > ditto > > > >? ? ? ? ?uint16_t *hash_list = (uint16_t *)&msgbuf[1]; > > > >? ? ? ? ?uint32_t mta_idx; > > > > @@ -399,7 +399,7 @@ ixgbe_vf_set_multicast(struct rte_eth_dev *dev, > > > > __rte_unused uint32_t vf, uint32 > > > >? ? ? ? ?const uint32_t IXGBE_MTA_BIT_SHIFT = 5; > > > >? ? ? ? ?const uint32_t IXGBE_MTA_BIT_MASK = (0x1 << IXGBE_MTA_BIT_SHIFT) > > > - > > > > 1; > > > >? ? ? ? ?uint32_t reg_val; > > > > -? ? ? ?int i; > > > > +? ? ? ?int16_t i; > > > ditto > > > > > > <rk> Same as above. > > > > > > > > > >? ? ? ? ?/* only so many hash values supported */ > > > >? ? ? ? ?nb_entries = RTE_MIN(nb_entries, IXGBE_MAX_VF_MC_ENTRIES); > > > > -- > > > > 1.9.1 > > > > > > >