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

[Jan Beulich <jbeulich@xxxxxxxx>]

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?

Jan