From mboxrd@z Thu Jan 1 00:00:00 1970 From: Avi Kivity Subject: Re: kvm-37 problem w/ 64-bit division in lapic.c Date: Wed, 12 Sep 2007 11:05:30 +0300 Message-ID: <46E79DCA.70101@qumranet.com> References: <46E3D369.8000401@qumranet.com> <20070909173640.6747418d@holly> <10EA09EFD8728347A513008B6B0DA77A02108583@pdsmsx411.ccr.corp.intel.com> <5f0e26840709100249y239692c2gcdd3938fc6b23b6c@mail.gmail.com> <20070910182628.5fc7090f@holly> Mime-Version: 1.0 Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Cc: kvm-devel-5NWGOfrQmneRv+LV9MX5uipxlwaOVQ5f@public.gmane.org To: Jindrich Makovicka Return-path: In-Reply-To: <20070910182628.5fc7090f@holly> List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Sender: kvm-devel-bounces-5NWGOfrQmneRv+LV9MX5uipxlwaOVQ5f@public.gmane.org Errors-To: kvm-devel-bounces-5NWGOfrQmneRv+LV9MX5uipxlwaOVQ5f@public.gmane.org List-Id: kvm.vger.kernel.org Jindrich Makovicka wrote: > On Mon, 10 Sep 2007 11:49:02 +0200 > "Jindrich Makovicka" wrote: > > >> On 9/10/07, Dong, Eddie wrote: >> >>> div64_32 is enough, does this function exist? >>> >> afaik, __div64_32 is architecture specific, but do_div() could be >> actually used here. >> > > This version should be faster. > > [please don't post patches with extensions like ".diff2", which don't show in the mail reader] > - u32 counter_passed; > + u64 counter_passed; > ktime_t passed, now = apic->timer.dev.base->get_time(); > u32 tmcct = apic_get_reg(apic, APIC_TMICT); > > @@ -512,8 +512,8 @@ static u32 apic_get_tmcct(struct kvm_lapic *apic) > } else > passed = ktime_sub(now, apic->timer.last_update); > > - counter_passed = div64_64(ktime_to_ns(passed), > - (APIC_BUS_CYCLE_NS * > apic->timer.divide_count)); > + counter_passed = ktime_to_ns(passed); > + do_div(counter_passed, APIC_BUS_CYCLE_NS * > apic->timer.divide_count); > tmcct -= counter_passed; What if counter_passed overflows? Sure, that means kvm wasn't scheduled for 4 seconds, but it could happen. -- error compiling committee.c: too many arguments to function ------------------------------------------------------------------------- This SF.net email is sponsored by: Microsoft Defy all challenges. Microsoft(R) Visual Studio 2005. http://clk.atdmt.com/MRT/go/vse0120000070mrt/direct/01/