[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index] Re: [Xen-devel] [PROPOSAL] Event channel for SMP-VMs: per-vCPU or per-OS?
>>> On 29.10.13 at 10:02, Luwei Cheng <chengluwei@xxxxxxxxx> wrote: > On Tue, Oct 29, 2013 at 4:19 PM, Jan Beulich <JBeulich@xxxxxxxx> wrote: >> >>> On 29.10.13 at 03:56, Luwei Cheng <chengluwei@xxxxxxxxx> wrote: >> > Hmm.. though all vCPUs can serve the events, the hypervisor delivers the >> > event to only "one" vCPU at at time, so only that vCPU can see this >> event. >> > Analytically no race condition will be introduced. >> >> No - an event is globally pending (at least in the old model, the >> situation is better with the new FIFO model), i.e. if more than >> one of the guest's vCPU-s allowed to service it would be looking >> at it simultaneously, they'd still need to arbitrate which one >> ought to handle it. >> >> So your proposed extension might need to be limited to the >> FIFO model. > > Thanks for your reply. Yes, you are right. My prior description was > incorrect. > When there are more than one vCPUs picking the event, even without > arbitrary, will it cause "correctness" problem? After the event is served by > the first entered vCPU, and the rest vCPUs just have noting to do in the > event handler (no much harm). That really depends on the handler. Plus it might be a performance and/or latency issue to run handlers that don't need to be run. Jan _______________________________________________ Xen-devel mailing list Xen-devel@xxxxxxxxxxxxx http://lists.xen.org/xen-devel
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