From mboxrd@z Thu Jan 1 00:00:00 1970 From: Radim Krcmar Subject: Re: [PATCH v3 2/6] KVM: X86: Implement PV IPIs in linux guest Date: Fri, 20 Jul 2018 11:51:36 +0200 Message-ID: <20180720095135.GA8330@flask> References: <1530598891-21370-1-git-send-email-wanpengli@tencent.com> <1530598891-21370-3-git-send-email-wanpengli@tencent.com> <20180719162826.GB11749@flask> Mime-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Transfer-Encoding: 8bit Cc: LKML , kvm , Paolo Bonzini , Vitaly Kuznetsov To: Wanpeng Li Return-path: Content-Disposition: inline In-Reply-To: Sender: linux-kernel-owner@vger.kernel.org List-Id: kvm.vger.kernel.org 2018-07-20 11:33+0800, Wanpeng Li: > On Fri, 20 Jul 2018 at 00:28, Radim Krčmář wrote: > > 2018-07-03 14:21+0800, Wanpeng Li: > > But because it is very similar to x2apic, I'd really need some real > > performance data to see if this benefits a real workload. > > Thanks for your review, Radim! :) I will find another real benchmark > instead of the micro one to evaluate the performance. Analyzing the cpu bitmap for every IPI request on a non-small guest (at least 32 VCPUs, ideally >256) during various workloads could also provide some insight regardless of workload/benchmark result -- we want to know how many VM exits we would save. > > > +static void kvm_send_ipi_all(int vector) > > > +{ > > > + __send_ipi_mask(cpu_online_mask, vector); > > > > These should be faster when using the native APIC shorthand -- is this > > the "Broadcast" in your tests? > > Not true, .send_IPI_all almost no callers though linux apic drivers > implement this hook, in addition, shortcut is not used for x2apic > mode(__x2apic_send_IPI_dest()), and very limited using in other > scenarios according to linux apic drivers. Good point, (xAPIC is using shorthands, so I didn't expect we'd stop doing so on x2APIC, but there was probably no need.) thanks.