From mboxrd@z Thu Jan 1 00:00:00 1970 From: Konrad Rzeszutek Wilk Subject: Re: [Xen-devel] [PATCH RFC v3 0/6] x86/idle: add halt poll support Date: Wed, 15 Nov 2017 16:31:31 -0500 Message-ID: <20171115213131.GB21113@char.us.oracle.com> References: <1510567565-5118-1-git-send-email-quan.xu0@gmail.com> Mime-Version: 1.0 Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Return-path: Content-Disposition: inline In-Reply-To: <1510567565-5118-1-git-send-email-quan.xu0@gmail.com> List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Sender: virtualization-bounces@lists.linux-foundation.org Errors-To: virtualization-bounces@lists.linux-foundation.org To: Quan Xu Cc: Yang Zhang , kvm@vger.kernel.org, linux-doc@vger.kernel.org, x86@kernel.org, linux-kernel@vger.kernel.org, virtualization@lists.linux-foundation.org, linux-fsdevel@vger.kernel.org, xen-devel@lists.xenproject.org List-Id: virtualization@lists.linuxfoundation.org On Mon, Nov 13, 2017 at 06:05:59PM +0800, Quan Xu wrote: > From: Yang Zhang > > Some latency-intensive workload have seen obviously performance > drop when running inside VM. The main reason is that the overhead > is amplified when running inside VM. The most cost I have seen is > inside idle path. Meaning an VMEXIT b/c it is an 'halt' operation ? And then going back in guest (VMRESUME) takes time. And hence your latency gets all whacked b/c of this? So if I understand - you want to use your _full_ timeslice (of the guest) without ever (or as much as possible) to go in the hypervisor? Which means in effect you don't care about power-saving or CPUfreq savings, you just want to eat the full CPU for snack? > > This patch introduces a new mechanism to poll for a while before > entering idle state. If schedule is needed during poll, then we > don't need to goes through the heavy overhead path. Schedule of what? The guest or the host?