Re: [patch V6 30/37] x86/entry: Convert reschedule interrupt to IDTENTRY_RAW

[Andy Lutomirski]

On Fri, May 15, 2020 at 5:10 PM Thomas Gleixner <tglx@xxxxxxxxxxxxx> wrote:
>
>
> The scheduler IPI does not need the full interrupt entry handling logic
> when the entry is from kernel mode.
>
> Even if tracing is enabled the only requirement is that RCU is watching and
> preempt_count has the hardirq bit on.
>
> The NOHZ tick state does not have to be adjusted. If the tick is not
> running then the CPU is in idle and the idle exit will restore the
> tick. Softinterrupts are not raised here, so handling them on return is not
> required either.
>
> User mode entry must go through the regular entry path as it will invoke
> the scheduler on return so context tracking needs to be in the correct
> state.
>
> Use IDTENTRY_RAW and the RCU conditional variants of idtentry_enter/exit()
> to guarantee that RCU is watching even if the IPI hits a RCU idle section.
>
> Remove the tracepoint static key conditional which is incomplete
> vs. tracing anyway because e.g. ack_APIC_irq() calls out into
> instrumentable code.
>
> Avoid the overhead of irq time accounting and introduce variants of
> __irq_enter/exit() so instrumentation observes the correct preempt count
> state.

Leftover text from an old version?

The code is Reviewed-by: Andy Lutomirski <luto@xxxxxxxxxx>