On Thu, Oct 26, 2023 at 01:20 PM -04, Michael S. Tsirkin wrote:
> On Thu, Oct 26, 2023 at 06:25:08PM +0200, Jakub Sitnicki wrote:
>> On Wed, Oct 25, 2023 at 04:53 PM +02, Jakub Sitnicki wrote:
>> > Since commit 65c7cdedeb30 ("genirq: Provide new interfaces for affinity
>> > hints") irq_set_affinity_hint is being phased out.
>> >
>> > Switch to new interfaces for setting and applying irq affinity hints.
>> >
>> > Signed-off-by: Jakub Sitnicki <ja...@cloudflare.com>
>> > ---
>> > v2:
>> > - Leave cpumask_copy as is. We can't pass pointer to stack memory as hint.
>> > Proposed a change to IRQ affinity interface to address this limitation:
>> > https://lore.kernel.org/r/20231025141517.375378-1-ja...@cloudflare.com
>>
>> Just a note to the ^ - if we wanted to get rid of msix_affinity_masks,
>> we could call irq_set_affinity directly, instead of calling it through
>> irq_set_affinity[_and]_hint.
>>
>> The hint wouldn't be available any more in /proc/irq/N/affinity_hint,
>> but the same information can be gathered from /proc/irq/N/smp_affinity.
>>
>> [...]
>
>
> So we are potentially breaking some userspace - what's the value we
> gain? Is there some way we can make disable_irq/enable_irq work?
> That would have a lot of value.
> There is an actual need for that in virtio for coco but we can't use
> these APIs with affinity managed IRQs.
Sorry, that is beyond my ken today.
I saw the comment in vp_modern_disable_vq_and_reset:
/* For the case where vq has an exclusive irq, call synchronize_irq() to
* wait for completion.
*
* note: We can't use disable_irq() since it conflicts with the affinity
* managed IRQ that is used by some drivers.
*/
... but I fail to follow how the two conflict.
Perhaps Xuah could shed some light here.
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