From mboxrd@z Thu Jan 1 00:00:00 1970 From: Avi Kivity Subject: Re: [PATCH RFC 2/4] Add yield hypercall for KVM guests Date: Mon, 02 Aug 2010 11:32:35 +0300 Message-ID: <4C5682A3.40409@redhat.com> References: <20100726061150.GB21699@linux.vnet.ibm.com> <20100726061445.GB8402@linux.vnet.ibm.com> <4C4DC3AD.7010404@goop.org> Mime-Version: 1.0 Content-Type: text/plain; charset=ISO-8859-1; format=flowed Content-Transfer-Encoding: 7bit Cc: vatsa@linux.vnet.ibm.com, Marcelo Tosatti , Gleb Natapov , linux-kernel@vger.kernel.org, npiggin@suse.de, kvm@vger.kernel.org, bharata@in.ibm.com, Balbir Singh , Jan Beulich To: Jeremy Fitzhardinge Return-path: In-Reply-To: <4C4DC3AD.7010404@goop.org> Sender: linux-kernel-owner@vger.kernel.org List-Id: kvm.vger.kernel.org On 07/26/2010 08:19 PM, Jeremy Fitzhardinge wrote: > On 07/25/2010 11:14 PM, Srivatsa Vaddagiri wrote: >> Add KVM hypercall for yielding vcpu timeslice. > > Can you do a directed yield? > A problem with directed yield is figuring out who to yield to. One idea is to look for a random vcpu that is not running and donate some runtime to it. In the best case, it's the lock holder and we cause it to start running. Middle case it's not the lock holder, but we lose enough runtime to stop running, so at least we don't waste cpu. Worst case we continue running not having woken the lock holder. Spin again, yield again hoping to find the right vcpu. -- error compiling committee.c: too many arguments to function