Re: [PATCH v2 3/7] x86/irq: limit interrupt movement done by fixup_irqs()

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

On Tue, Jun 11, 2024 at 11:59:39AM +0200, Jan Beulich wrote:
> On 10.06.2024 16:20, Roger Pau Monne wrote:
> > The current check used in fixup_irqs() to decide whether to move around
> > interrupts is based on the affinity mask, but such mask can have all bits 
> > set,
> > and hence is unlikely to be a subset of the input mask.  For example if an
> > interrupt has an affinity mask of all 1s, any input to fixup_irqs() that's 
> > not
> > an all set CPU mask would cause that interrupt to be shuffled around
> > unconditionally.
> > 
> > What fixup_irqs() care about is evacuating interrupts from CPUs not set on 
> > the
> > input CPU mask, and for that purpose it should check whether the interrupt 
> > is
> > assigned to a CPU not present in the input mask.  Assume that 
> > ->arch.cpu_mask
> > is a subset of the ->affinity mask, and keep the current logic that resets 
> > the
> > ->affinity mask if the interrupt has to be shuffled around.
> > 
> > Doing the affinity movement based on ->arch.cpu_mask requires removing the
> > special handling to ->arch.cpu_mask done for high priority vectors, 
> > otherwise
> > the adjustment done to cpu_mask makes them always skip the CPU interrupt
> > movement.
> > 
> > While there also adjust the comment as to the purpose of fixup_irqs().
> > 
> > Signed-off-by: Roger Pau Monné <roger.pau@xxxxxxxxxx>
> 
> Reviewed-by: Jan Beulich <jbeulich@xxxxxxxx>
> 
> Aiui this is independent of patch 1, so could go in while we still settle on
> how to word things there?

I think so, the issue patch 1 fixes is independent from the rest of the
series.

Thanks, Roger.