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SubjectRe: Kernel-managed IRQ affinity (cont)
On Thu, Dec 19, 2019 at 01:09:17PM -0500, Peter Xu wrote:
> On Fri, Dec 20, 2019 at 12:11:15AM +0800, Ming Lei wrote:
> > OK, please try the following patch:
> >
> >
> > diff --git a/include/linux/sched/isolation.h b/include/linux/sched/isolation.h
> > index 6c8512d3be88..0fbcbacd1b29 100644
> > --- a/include/linux/sched/isolation.h
> > +++ b/include/linux/sched/isolation.h
> > @@ -13,6 +13,7 @@ enum hk_flags {
> > HK_FLAG_TICK = (1 << 4),
> > HK_FLAG_DOMAIN = (1 << 5),
> > HK_FLAG_WQ = (1 << 6),
> > + HK_FLAG_MANAGED_IRQ = (1 << 7),
> > };
> >
> > #ifdef CONFIG_CPU_ISOLATION
> > diff --git a/kernel/irq/manage.c b/kernel/irq/manage.c
> > index 1753486b440c..0a75a09cc4e8 100644
> > --- a/kernel/irq/manage.c
> > +++ b/kernel/irq/manage.c
> > @@ -20,6 +20,7 @@
> > #include <linux/sched/task.h>
> > #include <uapi/linux/sched/types.h>
> > #include <linux/task_work.h>
> > +#include <linux/sched/isolation.h>
> >
> > #include "internals.h"
> >
> > @@ -212,12 +213,33 @@ int irq_do_set_affinity(struct irq_data *data, const struct cpumask *mask,
> > {
> > struct irq_desc *desc = irq_data_to_desc(data);
> > struct irq_chip *chip = irq_data_get_irq_chip(data);
> > + const struct cpumask *housekeeping_mask =
> > + housekeeping_cpumask(HK_FLAG_MANAGED_IRQ);
> > int ret;
> > + cpumask_var_t tmp_mask;
> >
> > if (!chip || !chip->irq_set_affinity)
> > return -EINVAL;
> >
> > - ret = chip->irq_set_affinity(data, mask, force);
> > + if (!zalloc_cpumask_var(&tmp_mask, GFP_KERNEL))
> > + return -EINVAL;
> > +
> > + /*
> > + * Userspace can't change managed irq's affinity, make sure
> > + * that isolated CPU won't be selected as the effective CPU
> > + * if this irq's affinity includes both isolated CPU and
> > + * housekeeping CPU.
> > + *
> > + * This way guarantees that isolated CPU won't be interrupted
> > + * by IO submitted from housekeeping CPU.
> > + */
> > + if (irqd_affinity_is_managed(data) &&
> > + cpumask_intersects(mask, housekeeping_mask))
> > + cpumask_and(tmp_mask, mask, housekeeping_mask);
> > + else
> > + cpumask_copy(tmp_mask, mask);
> > +
> > + ret = chip->irq_set_affinity(data, tmp_mask, force);
> > switch (ret) {
> > case IRQ_SET_MASK_OK:
> > case IRQ_SET_MASK_OK_DONE:
> > @@ -229,6 +251,8 @@ int irq_do_set_affinity(struct irq_data *data, const struct cpumask *mask,
> > ret = 0;
> > }
> >
> > + free_cpumask_var(tmp_mask);
> > +
> > return ret;
> > }
> >
> > diff --git a/kernel/sched/isolation.c b/kernel/sched/isolation.c
> > index 9fcb2a695a41..008d6ac2342b 100644
> > --- a/kernel/sched/isolation.c
> > +++ b/kernel/sched/isolation.c
> > @@ -163,6 +163,12 @@ static int __init housekeeping_isolcpus_setup(char *str)
> > continue;
> > }
> >
> > + if (!strncmp(str, "managed_irq,", 12)) {
> > + str += 12;
> > + flags |= HK_FLAG_MANAGED_IRQ;
> > + continue;
> > + }
> > +
> > pr_warn("isolcpus: Error, unknown flag\n");
> > return 0;
> > }
>
> Thanks for the quick patch. I'll test after my current round of tests
> finish and update. I'll probably believe this will work for us as
> long as it "functionally" works :) (after all it won't even need a RT
> environment because it's really about where to put some IRQs). So
> IMHO the more important thing is whether such a solution could be
> acceptable by the upstream.

I've tested this patch, it works for us. "isolcpus=managed_irq,2-9"
gives me:

[root@rt-vm 32]# pwd
/proc/irq/32
[root@rt-vm 32]# cat smp_affinity
003
[root@rt-vm 32]# cat effective_affinity
001

Thomas, do you think Ming's solution could be accepted?

Thanks,

--
Peter Xu

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