On 15.09.2017 15:17, Alex Bennée wrote: > > David Hildenbrand <da...@redhat.com> writes: > >> On 13.09.2017 18:13, Alex Bennée wrote: >>> >>> David Hildenbrand <da...@redhat.com> writes: >>> >>>> Specifying more than 1 CPU (e.g. -smp 5) leads to SIGP errors (the >>>> guest tries to bring these CPUs up but fails), because we don't support >>>> multiple CPUs on s390x under TCG. >>>> >>>> Let's bail out if more than 1 is specified, so we don't raise people's >>>> hope. >>> >>> Why does this restriction exist? Without MTTCG enabled -smp > 1 should >>> be safe from any races. >> >> Because the actual SIGP code (instruction to start/stop ... CPUs) is not >> implemented yet. > > Ahh OK, I assume something like ARM's PCSI interface then. > > When you do get around to implementing just ensure you use the async > mechanism to initialise the target processor state to avoid races in > MTTCG. Essentially you queue the work up on the target and then it is > run before the powered up vCPU starts running code.
One step at a time, right now I only test with single threaded. MTTCG is the next step. But I have a good feeling about mttcg, at least speaking about the SIGP implementation (for the "critical" stuff - start, stop, initialize - I reuse the KVM code which uses even sync work). > > -- > Alex Bennée > -- Thanks, David
