Philippe Mathieu-Daudé <f4...@amsat.org> writes:
> (Cc'ing qemu-devel@ mailing list since this is a development question). > > On 9/19/21 19:44, Robert Henry wrote: >> What is the range of the values for vcpu_index given to callbacks, such as: >> >> typedef void (*qemu_plugin_vcpu_udata_cb_t)(unsigned int vcpu_index, >> void *userdata); >> >> Empirically, when QEMU is in system mode, the maximum vcpu_index is 1 >> less than the -smp cpus=$(NCPUS) value. >> >> Empirically, when QEMU is in user mode, the values for vcpu_index slowly >> increase without an apparent upper bound known statically (or when the >> plugin is loaded?). > > Isn't it related to clone() calls? I'd expect new threads use > a new vCPU, incrementing vcpu_index. But that is just a guess > without having looked at the code to corroborate... It's exactly that - in user-mode each thread is modelled using a new virtual CPU so a heavily threaded application will slowly grow the maximum index. If you want to track the creation of these threads you can use qemu_plugin_register_vcpu_init_cb to track the creation of the new vCPUs. It's more this reason the recently added cache modelling plugin does vcpu_index % cores to bound the simulated cache the thread affects. > > Regards, > > Phil. -- Alex Bennée
