From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-pd0-f182.google.com (mail-pd0-f182.google.com [209.85.192.182]) by dpdk.org (Postfix) with ESMTP id 4C28F1F5 for ; Tue, 16 Dec 2014 21:13:38 +0100 (CET) Received: by mail-pd0-f182.google.com with SMTP id p10so14611926pdj.27 for ; Tue, 16 Dec 2014 12:13:37 -0800 (PST) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=gmail.com; s=20120113; h=mime-version:in-reply-to:references:date:message-id:subject:from:to :cc:content-type; bh=p+EmRNOHvLz21vu0GyyCpuRU+lLBUwdiNmaTeePOdog=; b=Z6dsEXbjWl+t/cnQkWM5ZXbzdcZhXdcz1EuOaqiWv6b4FW9BZU2vP7j3rhObURSgQZ KGglpnL++PLlnP5xmwJDKGqK2Y162qiR7eYs/CS+N6ERI0Lxk0c316NuY1d891HpdFsm c6+ELF/OcDA+nd+OCf0cGjnBaaGLIlDfmeNc8V0RDLbacWa1pAAifNisb3dYDXLtK9QF Xiu62i7C2n20UT3o/+5o/NiCMU93tObcMCNuFrzvmW0e3uvKP+B5OWhawTAoLqo9D06P JY+/ZPph7MJPaJA+08fsm10tbIhWZV8lTjBXx+H+rWMMUrD1bfP1fbHEcvGfbRk/q9nF Lh3Q== MIME-Version: 1.0 X-Received: by 10.66.150.74 with SMTP id ug10mr64821546pab.68.1418760817311; Tue, 16 Dec 2014 12:13:37 -0800 (PST) Received: by 10.70.136.201 with HTTP; Tue, 16 Dec 2014 12:13:37 -0800 (PST) In-Reply-To: <2601191342CEEE43887BDE71AB977258213C1316@IRSMSX105.ger.corp.intel.com> References: <20141213103921.GA1162@localhost.localdomain> <2601191342CEEE43887BDE71AB977258213C1316@IRSMSX105.ger.corp.intel.com> Date: Tue, 16 Dec 2014 12:13:37 -0800 Message-ID: From: Ravi Kerur To: "Ananyev, Konstantin" Content-Type: text/plain; charset=ISO-8859-1 X-Content-Filtered-By: Mailman/MimeDel 2.1.15 Cc: "dev@dpdk.org" Subject: Re: [dpdk-dev] [PATCH] Minor fixes in rte_common.h file. X-BeenThere: dev@dpdk.org X-Mailman-Version: 2.1.15 Precedence: list List-Id: patches and discussions about DPDK List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , X-List-Received-Date: Tue, 16 Dec 2014 20:13:38 -0000 On Tue, Dec 16, 2014 at 9:23 AM, Ananyev, Konstantin < konstantin.ananyev@intel.com> wrote: > > > > > -----Original Message----- > > From: dev [mailto:dev-bounces@dpdk.org] On Behalf Of Ravi Kerur > > Sent: Tuesday, December 16, 2014 4:47 PM > > To: Neil Horman > > Cc: dev@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 > 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 > > > > --- > > > > 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? > > > > > > > > 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 > 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. > > > > > }) > > > > > > > > /** > > > > @@ -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 > > > > > > 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 > > > > > > > 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 > > > > > > Same as above. > > > > > > > > > > /* only so many hash values supported */ > > > > nb_entries = RTE_MIN(nb_entries, IXGBE_MAX_VF_MC_ENTRIES); > > > > -- > > > > 1.9.1 > > > > > > > >