Re: [PATCH qemu] fdmon-io_uring: avoid idle event loop being accounted as IO wait

[Thomas Lamprecht <t.lamprecht@proxmox.com>]

Am 28.04.26 um 16:40 schrieb Fiona Ebner:
>>>>> +     * Number of in-flight requests to be accounted for IO wait.
>>>>> +     * Must be accessed using atomics.
>>>
>>> why though? AioContext is strictly single-threaded nowadays and (enqueue)
>>> and process_cqe (dequeue) run on the owning thread. Or is this just
>>> defensive protection for potential future changes - as it's cheap I'm
>>> fine with it, just wanted to know if I'm overlooking something here.
>>
>> No, looking over it again, I think you are right. I was under the
>> impression that somehow vCPUs might also add SQEs, but no, that happens
>> in the iothread already.
>
> vCPU threads might reach fdmon_io_uring_wait() via aio_poll() (e.g. via
> virtio_scsi_dataplane_stop() during Linux guest boot), so atomics are
> really necessary.

Ack, they are cheap enough for us to not really care here in any
case, but good to actually know about why they are required.