On 29/05/2017 15:58, Andrew Jones wrote:
> Paolo inspired me to add x86's on_cpu and on_cpu_asynch to ARM's API.
> I messed around with it a while, but haven't really settled on what
> I want to do. I played with the following approaches:
> - wfe/sev, requires the concept of an idle state and knowing that the
> target CPU is in that state - i.e. no arbitrary preemption.
WFE really is just a power-save NOP. I think you'd do something like
spin_lock(&dest->ipi_lock);
assert(dest->ipi_cb == NULL);
dest->ipi_cb = fn;
dest->ipi_opaque = opaque;
spin_unlock(&dest->ipi_lock);
asm("dsb; sev");
while (dest->ipi_cb != NULL)
asm("wfe");
and on the other side:
while (dest->ipi_cb == NULL)
asm("wfe");
spin_lock(&dest->ipi_lock);
cb = dest->ipi_cb;
opaque = dest->ipi_opaque;
dest->ipi_cb = NULL;
spin_unlock(&dest->ipi_lock);
asm("dsb; sev");
cb(opaque);
Thanks,
Paolo
> - IPI, allows arbitrary preemption, but requires the GIC to be setup
> enough to receive SGIs and also a dedicated SGI for the scheduling
> - PSCI, poweroff state isn't better than an idle state, and PSCI works
> asynchronously wrt CPUs
