Re: mlx5 broken affinity

[Thomas Gleixner <tglx@linutronix.de>]

On Thu, 2 Nov 2017, Sagi Grimberg wrote:

> 
> > This wasn't to start a debate about which allocation method is the
> > perfect solution. I am perfectly happy with the new default, the part
> > that is broken is to take away the user's option to reassign the
> > affinity. That is a bug and it needs to be fixed!
> 
> Well,
> 
> I would really want to wait for Thomas/Christoph to reply, but this
> simple change fixed it for me:
> --
> diff --git a/kernel/irq/manage.c b/kernel/irq/manage.c
> index 573dc52b0806..eccd06be5e44 100644
> --- a/kernel/irq/manage.c
> +++ b/kernel/irq/manage.c
> @@ -146,8 +146,7 @@ bool irq_can_set_affinity_usr(unsigned int irq)
>  {
>         struct irq_desc *desc = irq_to_desc(irq);
> 
> -       return __irq_can_set_affinity(desc) &&
> -               !irqd_affinity_is_managed(&desc->irq_data);
> +       return __irq_can_set_affinity(desc);

Which defeats the whole purpose of the managed facility, which is _not_ to
break the affinities on cpu offline and bring the interrupt back on the CPU
when it comes online again.

What I can do is to have a separate flag, which only uses the initial
distribution mechanism, but I really want to have Christophs opinion on
that.

Thanks,

	tglx