On 20/11/24 15:23, Frederic Weisbecker wrote:
Ah but there is CT_STATE_GUEST and I see the last patch also applies that to CT_STATE_IDLE.
So that could be:
bool ct_set_cpu_work(unsigned int cpu, unsigned int work) { struct context_tracking *ct = per_cpu_ptr(&context_tracking, cpu); unsigned int old; bool ret = false;
preempt_disable();
old = atomic_read(&ct->state);
/* CT_STATE_IDLE can be added to last patch here */ if (!(old & (CT_STATE_USER | CT_STATE_GUEST))) { old &= ~CT_STATE_MASK; old |= CT_STATE_USER; }
Hmph, so that lets us leverage the cmpxchg for a !CT_STATE_KERNEL check, but we get an extra loop if the target CPU exits kernelspace not to userspace (e.g. vcpu or idle) in the meantime - not great, not terrible.
At the cost of one extra bit for the CT_STATE area, with CT_STATE_KERNEL=1 we could do:
old = atomic_read(&ct->state); old &= ~CT_STATE_KERNEL;