From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from dpdk.org (dpdk.org [92.243.14.124]) by dpdk.space (Postfix) with ESMTP id 5B406A05D3 for ; Fri, 26 Apr 2019 14:03:52 +0200 (CEST) Received: from [92.243.14.124] (localhost [127.0.0.1]) by dpdk.org (Postfix) with ESMTP id E0B4B1B122; Fri, 26 Apr 2019 14:03:49 +0200 (CEST) Received: from mga18.intel.com (mga18.intel.com [134.134.136.126]) by dpdk.org (Postfix) with ESMTP id 3ACFA1B0FC; Fri, 26 Apr 2019 14:03:47 +0200 (CEST) X-Amp-Result: SKIPPED(no attachment in message) X-Amp-File-Uploaded: False Received: from orsmga002.jf.intel.com ([10.7.209.21]) by orsmga106.jf.intel.com with ESMTP/TLS/DHE-RSA-AES256-GCM-SHA384; 26 Apr 2019 05:03:46 -0700 X-ExtLoop1: 1 X-IronPort-AV: E=Sophos;i="5.60,397,1549958400"; d="scan'208";a="153966899" Received: from aburakov-mobl1.ger.corp.intel.com (HELO [10.251.92.20]) ([10.251.92.20]) by orsmga002.jf.intel.com with ESMTP; 26 Apr 2019 05:03:45 -0700 To: "Hunt, David" , dev@dpdk.org Cc: stable@dpdk.org References: <20190426084415.3979-1-david.hunt@intel.com> <109520e2-b6fc-418c-81e9-03b7821ea2ed@intel.com> From: "Burakov, Anatoly" Message-ID: <7f275a33-f5d4-d8e4-f637-4a75f5bb50f9@intel.com> Date: Fri, 26 Apr 2019 13:03:44 +0100 User-Agent: Mozilla/5.0 (Windows NT 10.0; WOW64; rv:60.0) Gecko/20100101 Thunderbird/60.6.1 MIME-Version: 1.0 In-Reply-To: <109520e2-b6fc-418c-81e9-03b7821ea2ed@intel.com> Content-Type: text/plain; charset="UTF-8"; format="flowed" Content-Language: en-US Content-Transfer-Encoding: 8bit Subject: Re: [dpdk-dev] [PATCH v1] examples/vm_power_manager: fix overflowed return value X-BeenThere: dev@dpdk.org X-Mailman-Version: 2.1.15 Precedence: list List-Id: DPDK patches and discussions List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Errors-To: dev-bounces@dpdk.org Sender: "dev" Message-ID: <20190426120344.Otaxd6HtYh8M7teua0xa1ZpFWOrtQqMjBAiD_4waFBk@z> On 26-Apr-19 12:14 PM, Hunt, David wrote: > Hi Anatoly, > > On 26/4/2019 11:29 AM, Burakov, Anatoly wrote: >> On 26-Apr-19 9:44 AM, David Hunt wrote: >>> Coverity complains about the return of a value that may >>> possibly overflow because of a multiply. Limit the value >>> so it cannot overflow. >>> >>> Coverity issue: 337677 >>> Fixes: 4b1a631b8a ("examples/vm_power: add oob monitoring functions") >>> CC: stable@dpdk.org >>> Signed-off-by: David Hunt >>> --- >>>   examples/vm_power_manager/oob_monitor_x86.c | 5 ++++- >>>   1 file changed, 4 insertions(+), 1 deletion(-) >>> >>> diff --git a/examples/vm_power_manager/oob_monitor_x86.c >>> b/examples/vm_power_manager/oob_monitor_x86.c >>> index ebd96b205..2074eec1e 100644 >>> --- a/examples/vm_power_manager/oob_monitor_x86.c >>> +++ b/examples/vm_power_manager/oob_monitor_x86.c >>> @@ -99,7 +99,10 @@ apply_policy(int core) >>>           return -1.0; >>>       } >>>   -    ratio = (float)miss_diff * (float)100 / (float)hits_diff; >>> +    ratio = (float)miss_diff / (float)hits_diff; >>> +    if (ratio > 1.0) >>> +        ratio = 1.0; >>> +    ratio *= 100.0f; >> >> It should probably be the other way around - multiply first, then >> clamp. Also, please use RTE_MIN. >> > I tried that, but coverity still sees an overflow condition. I need to > clamp first, then multiply. Then coverity is happy. That's weird. This may be a bug in Coverity then. Please correct me if i'm wrong, but floating point formats aren't precise, so by doing multiplication on a value that doesn't exceed 1.0, you may very well end up with a value that does exceed 100 by a tiny bit on account of floating point approximations, rounding errors etc. The question is, do we want correct code, or do we want to keep Coverity happy? :) I'll have a look at the coverity issue itself, maybe i'm missing something here... > > Also, do you really want me to change to use RTE_MIN? I honestly prefer > the code as it is. No strong opinion here. > > > >>>         if (ratio < ci->branch_ratio_threshold) >>>           power_manager_scale_core_min(core); >>> >> >> > -- Thanks, Anatoly