On 13/11/2017 11:14, Alex Bennée wrote: > > Pavel Dovgalyuk <dovga...@ispras.ru> writes: > >>> From: Paolo Bonzini [mailto:pbonz...@redhat.com] >>>> From: "David Hildenbrand" <da...@redhat.com> >>>> On 02.11.2017 12:08, Paolo Bonzini wrote: >>>>> On 31/10/2017 12:26, Pavel Dovgalyuk wrote: >>>>>> From: Alex Bennée <alex.ben...@linaro.org> >>>>>> >>>>>> Now the only real need to hold the BQL is for when we sleep on the >>>>>> cpu->halt conditional. The lock is actually dropped while the thread >>>>>> sleeps so the actual window for contention is pretty small. This also >>>>>> means we can remove the special case hack for exclusive work and >>>>>> simply declare that work no longer has an implicit BQL held. This >>>>>> isn't a major problem async work is generally only changing things in >>>>>> the context of its own vCPU. If it needs to work across vCPUs it >>>>>> should be using the exclusive mechanism or possibly taking the lock >>>>>> itself. >>>>>> >>>>>> Signed-off-by: Alex Bennée <alex.ben...@linaro.org> >>>>>> Tested-by: Pavel Dovgalyuk <pavel.dovga...@ispras.ru> >>>>> >>>>> At least cpu_throttle_thread would fail with this patch. >>>>> >>>>> Also I am not sure if the s390 SIGP handlers are ready for this. >>>>> >>>> >>>> We have a global lock to the SIGP "facility". However we need the BQL in >>>> order to inject interrupts into CPUs (otherwise it would trigger an >>>> assert when injecting). >>>> >>>> We inject Restart and Stop interrupts from run_on_cpu. This requires the >>>> BQL. So Paolo should be right, this change would break s390x. >>> >>> I had some patches to access interrupt_request with the atomic builtins. If >>> Pavel can first extract the other changes to the icount mechanism, I can >>> update them. >> >> What changes do you mean here? >> I'm not sure that I understand clearly how threads interact with BQL. >> These patches were authored by Alex and we'll have to get him into the >> discussion. > > Do you want me to re-spin my sub-set of the patches as a new base?
I think the first part to be merged is changes to cpu-exec.c and friends. These might even go into 2.11. Paolo
