Messages in this thread Patch in this message | | | Date | Mon, 24 Jan 2022 11:24:52 +0000 | From | Marc Zyngier <> | Subject | Re: [PATCH] irqchip/gic-v3-its: Select housekeeping CPUs preferentially for managed IRQs |
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+ John Garry, as he was reporting issues around the same piece of code[1]
On Mon, 24 Jan 2022 07:34:40 +0000, Xiongfeng Wang <wangxiongfeng2@huawei.com> wrote: > > When using kernel parameter 'isolcpus=managed_irq,xxxx' to bind the > managed IRQs to housekeeping CPUs, the effective_affinity sometimes > still contains the non-housekeeping CPUs. > > irq_do_set_affinity() passes the housekeeping cpumask to > chip->irq_set_affinity(), but ITS driver select CPU according to > irq_common_data->affinity. While 'irq_common_data->affinity' is updated > after chip->irq_set_affinity() is called in irq_do_set_affinity(). Also > 'irq_common_data->affinity' may contains non-housekeeping CPUs. I found > the below link explaining the reason. > https://www.mail-archive.com/linux-kernel@vger.kernel.org/msg2267032.html > > To modify CPU selecting logic to prefer housekeeping CPUs, select CPU > from the input cpumask parameter first. If none of it is online, then > select CPU from 'irq_common_data->affinity'. > > Signed-off-by: Xiongfeng Wang <wangxiongfeng2@huawei.com> > --- > drivers/irqchip/irq-gic-v3-its.c | 5 ++++- > 1 file changed, 4 insertions(+), 1 deletion(-) > > diff --git a/drivers/irqchip/irq-gic-v3-its.c b/drivers/irqchip/irq-gic-v3-its.c > index d25b7a864bbb..17c15d3b2784 100644 > --- a/drivers/irqchip/irq-gic-v3-its.c > +++ b/drivers/irqchip/irq-gic-v3-its.c > @@ -1624,7 +1624,10 @@ static int its_select_cpu(struct irq_data *d, > > cpu = cpumask_pick_least_loaded(d, tmpmask); > } else { > - cpumask_and(tmpmask, irq_data_get_affinity_mask(d), cpu_online_mask); > + cpumask_and(tmpmask, aff_mask, cpu_online_mask); > + if (cpumask_empty(tmpmask)) > + cpumask_and(tmpmask, irq_data_get_affinity_mask(d), > + cpu_online_mask);
I think that the online_cpu_mask logical and is a bit wrong. A managed interrupt should be able to target an offline CPU:
diff --git a/drivers/irqchip/irq-gic-v3-its.c b/drivers/irqchip/irq-gic-v3-its.c index eb0882d15366..0cea46bdaf99 100644 --- a/drivers/irqchip/irq-gic-v3-its.c +++ b/drivers/irqchip/irq-gic-v3-its.c @@ -1620,7 +1620,7 @@ static int its_select_cpu(struct irq_data *d, cpu = cpumask_pick_least_loaded(d, tmpmask); } else { - cpumask_and(tmpmask, irq_data_get_affinity_mask(d), cpu_online_mask); + cpumask_copy(tmpmask, aff_mask); /* If we cannot cross sockets, limit the search to that node */ if ((its_dev->its->flags & ITS_FLAGS_WORKAROUND_CAVIUM_23144) && We still have an issue when the system hasn't booted with all its CPUs, as the corresponding collections aren't initialised and we end-up in a rather bad place.
M.
[1] https://lore.kernel.org/r/78615d08-1764-c895-f3b7-bfddfbcbdfb9@huawei.com
-- Without deviation from the norm, progress is not possible.
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