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;
