On 5/21/24 5:00 AM, Thomas Gleixner wrote: > On Wed, May 15 2024 at 12:51, Dongli Zhang wrote: >> On 5/13/24 3:46 PM, Thomas Gleixner wrote: >>> So yes, moving the invocation of irq_force_complete_move() before the >>> irq_needs_fixup() call makes sense, but it wants this to actually work >>> correctly: >>> @@ -1097,10 +1098,11 @@ void irq_force_complete_move(struct irq_ >>> goto unlock; >>> >>> /* >>> - * If prev_vector is empty, no action required. >>> + * If prev_vector is empty or the descriptor was previously >>> + * not on the outgoing CPU no action required. >>> */ >>> vector = apicd->prev_vector; >>> - if (!vector) >>> + if (!vector || apicd->prev_cpu != smp_processor_id()) >>> goto unlock; >>> >> >> The above may not work. migrate_one_irq() relies on irq_force_complete_move() to >> always reclaim the apicd->prev_vector. Otherwise, the call of >> irq_do_set_affinity() later may return -EBUSY. > > You're right. But that still can be handled in irq_force_complete_move() > with a single unconditional invocation in migrate_one_irq(): > > cpu = smp_processor_id(); > if (!vector || (apicd->cur_cpu != cpu && apicd->prev_cpu != cpu)) > goto unlock; The current affine is apicd->cpu :) Thank you very much for the suggestion! > > because there are only two cases when a cleanup is required: > > 1) The outgoing CPU is the current target > > 2) The outgoing CPU was the previous target > > No? I agree with this statement. My only concern is: while we use "apicd->cpu", the irq_needs_fixup() uses a different way. It uses d->common->effective_affinity or d->common->affinity to decide whether to move forward to migrate the interrupt. I have spent some time reading about the discussion that happened in the year 2017 (below link). According to my understanding, CONFIG_GENERIC_IRQ_EFFECTIVE_AFF_MASK always relies on CONFIG_SMP, and we do not have the chance to encounter the issue for x86. https://lore.kernel.org/all/alpine.DEB.2.20.1710042208400.2406@nanos/T/#u I have tested the new patch for a while and never encountered any issue. Therefore, I will send v2. Thank you very much for all suggestions! Dongli Zhang
