On Fri, Sep 22, 2017 at 09:16:40AM -0300, Marcelo Tosatti wrote: > On Fri, Sep 22, 2017 at 12:00:05PM +0200, Peter Zijlstra wrote: > > On Thu, Sep 21, 2017 at 10:10:41PM -0300, Marcelo Tosatti wrote: > > > When executing guest vcpu-0 with FIFO:1 priority, which is necessary > > > to > > > deal with the following situation: > > > > > > VCPU-0 (housekeeping VCPU) VCPU-1 (realtime VCPU) > > > > > > raw_spin_lock(A) > > > interrupted, schedule task T-1 raw_spin_lock(A) (spin) > > > > > > raw_spin_unlock(A) > > > > > > Certain operations must interrupt guest vcpu-0 (see trace below). > > > > Those traces don't make any sense. All they include is kvm_exit and you > > can't tell anything from that. > > Hi Peter, > > OK lets describe whats happening: > > With QEMU emulator thread and vcpu-0 sharing a physical CPU > (which is a request from several NFV customers, to improve > guest packing), the following occurs when the guest generates > the following pattern: > > 1. submit IO. > 2. busy spin. User-space spinning is a bad idea in general and terminally broken in a RT setup. Sounds like you need to go fix qemu to not suck.
