Re: [PATCH v2 5/6] x86/idle: Implement a new MWAIT IPI-elision algorithm

[Roger Pau Monné <roger.pau@xxxxxxxxxx>]

On Fri, Jul 04, 2025 at 05:34:09PM +0100, Andrew Cooper wrote:
> In order elide IPIs, we must be able to identify whether a target CPU is in
> MWAIT at the point it is woken up.  i.e. the store to wake it up must also
> identify the state.
> 
> Create a new in_mwait variable beside __softirq_pending, so we can use a
> CMPXCHG to set the softirq while also observing the status safely.  Implement
> an x86 version of arch_pend_softirq() which does this.
> 
> In mwait_idle_with_hints(), advertise in_mwait, with an explanation of
> precisely what it means.  X86_BUG_MONITOR can be accounted for simply by not
> advertising in_mwait.
> 
> Signed-off-by: Andrew Cooper <andrew.cooper3@xxxxxxxxxx>

Acked-by: Roger Pau Monné <roger.pau@xxxxxxxxxx>

Thanks, Roger.