> On Feb. 10, 2014, 12:28 a.m., Steve Reinhardt wrote: > > You comment that "we are currently limited to configurations where there is > > only one KVM CPU per event queue"... can you expand on this? I.e., why > > can't I have multiple KVM CPUs per event queue and timeslice among them? > > Or is that not what you meant? > > Andreas Sandberg wrote: > The limitation at the moment is because we can't multiplex between KVM > CPUs in the same event queue. This is caused by the way we simulated until > the next event (we look into the future and request an exit when the next > event is due), if there is another KVM CPU executing, we'll see that one on > the same or a nearby tick. It might be possible to get multiplexing to work > by ignoring KVM events when we look into the local event queue to calculate > when to exit from KVM. > > Steve Reinhardt wrote: > I see. So this would be a limitation with the current single-threaded > model as well, right? I guess I was reading too much into it and thinking > this was a new limitation due to the multiple queues.
That is correct. Without this patch, the KVM implementation only supports one CPU at a time. > On Feb. 10, 2014, 12:28 a.m., Steve Reinhardt wrote: > > src/cpu/kvm/base.cc, line 1111 > > <http://reviews.gem5.org/r/2159/diff/1/?file=39259#file39259line1111> > > > > I wasn't sure why you changed from sigprocmask to pthread_sigmask, but > > on googling for the answer I found this: > > http://stackoverflow.com/questions/2170672/sigprocmask-causing-segfault > > > > So it makes sense to me now, but might be worth a mention in the commit > > message. > > Andreas Sandberg wrote: > That wasn't the problem I encountered. The problem I had was that I need > to ensure that only the thread executing the KVM CPU's event queue should be > affected by the new signal mask. sigprocmask might actually work -- I don't > know -- but the man page is pretty clear on the subject: > > "The use of sigprocmask() is unspecified in a multithreaded process; see > pthread_sigmask(3)." > > > Steve Reinhardt wrote: > Right... I didn't necessarily mean the segfault, I just noticed at that > link a similar comment about sigprocmask only being valid for single-threaded > processes. Anyway, adding a sentence like "Switched from sigprocmask() to > pthread_sigmask() because the former is not compatible with multiple threads" > to the commit message would be nice for those of us not familiar with these > details. I'll add that and include a line about the change in timer signal delivery. - Andreas ----------------------------------------------------------- This is an automatically generated e-mail. To reply, visit: http://reviews.gem5.org/r/2159/#review4896 ----------------------------------------------------------- On Feb. 10, 2014, 10:45 a.m., Andreas Sandberg wrote: > > ----------------------------------------------------------- > This is an automatically generated e-mail. To reply, visit: > http://reviews.gem5.org/r/2159/ > ----------------------------------------------------------- > > (Updated Feb. 10, 2014, 10:45 a.m.) > > > Review request for Default. > > > Repository: gem5 > > > Description > ------- > > Changeset 10062:4fea5050f4f2 > --------------------------- > kvm: Add support for multi-system simulation > > The introduction of parallel event queues added most of the support > needed to run multiple VMs (systems) within the same gem5 > instance. This changeset fixes up signal delivery so that KVM's > control signals are delivered to the thread that executes the CPU's > event queue. > > There are currently no facilities to multiplex between multiple KVM > CPUs in the same event queue, we are therefore limited to > configurations where there is only one KVM CPU per event queue. In > practice, this means that multi-system configurations can be > simulated, but not multiple CPUs in a shared-memory configuration. > > > Diffs > ----- > > src/cpu/kvm/base.hh 3b0d0c988ed6 > src/cpu/kvm/base.cc 3b0d0c988ed6 > src/cpu/kvm/timer.cc 3b0d0c988ed6 > > Diff: http://reviews.gem5.org/r/2159/diff/ > > > Testing > ------- > > Tested boot and interactive use of single CPU system -- works. > Tested boot of dual-system configuration and interactive use -- works. > > Did not run regressions as the current tests do not test KVM functionality. > > Also available from the multisys branch in git://github.com/andysan/gem5.git. > > > Thanks, > > Andreas Sandberg > > _______________________________________________ gem5-dev mailing list [email protected] http://m5sim.org/mailman/listinfo/gem5-dev
