From mboxrd@z Thu Jan 1 00:00:00 1970 From: Srivatsa Vaddagiri Subject: Re: [PATCH RFC V6 0/11] Paravirtualized ticketlocks Date: Sat, 31 Mar 2012 09:39:15 +0530 Message-ID: <20120331040915.GF13345@linux.vnet.ibm.com> References: <20120321102041.473.61069.sendpatchset@codeblue.in.ibm.com> <4F7616F5.4070000@zytor.com> <20120331040745.GC14030@linux.vnet.ibm.com> Reply-To: Srivatsa Vaddagiri Mime-Version: 1.0 Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Return-path: Content-Disposition: inline In-Reply-To: <20120331040745.GC14030@linux.vnet.ibm.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: Thomas Gleixner Cc: the arch/x86 maintainers , KVM , Konrad Rzeszutek Wilk , Peter Zijlstra , Stefano Stabellini , Raghavendra K T , LKML , Andi Kleen , Avi Kivity , Jeremy Fitzhardinge , "H. Peter Anvin" , Attilio Rao , Ingo Molnar , Virtualization , Linus Torvalds , Xen Devel , Stephan Diestelhorst List-Id: virtualization@lists.linuxfoundation.org * Srivatsa Vaddagiri [2012-03-31 09:37:45]: > The issue is with ticketlocks though. VCPUs could go into a spin w/o > a lock being held by anybody. Say VCPUs 1-99 try to grab a lock in > that order (on a host with one cpu). VCPU1 wins (after VCPU0 releases it) > and releases the lock. VCPU1 is next eligible to take the lock. If Sorry I meant to say "VCPU2 is next eligible ..." > that is not scheduled early enough by host, then remaining vcpus would keep > spinning (even though lock is technically not held by anybody) w/o making > forward progress. > > In that situation, what we really need is for the guest to hint to host > scheduler to schedule VCPU1 early (via yield_to or something similar). s/VCPU1/VCPU2 .. - vatsa