Re: Re: [PATCH] block: Avoid polling configuration errors

hexue
2024-06-06T01:09:02Z

On Sat, Jun 1, 2024 at 00:38:49 -0700, Christoph Hellwig wrote:
>On Fri, May 31, 2024 at 05:10:15PM +0800, hexue wrote:
>> Here's a misconfigured if application is doing polled IO
>> for devices that don't have a poll queue, the process will
>> continue to do syscall between user space and kernel space,
>> as in normal poll IO, CPU utilization will be 100%. IO actually
>> arrives through interruption.
>>
>> This patch returns a signal that does not support the operation
>> when the underlying device does not have a poll queue, avoiding
>> performance and CPU simultaneous loss.
>
>This feels like the wrong place to check for this.
>
>As we've dropped synchronous polling we now only support
>thead based polling, right now only through io_uring.
>
>So we need to ensure REQ_POLLED doesn't even get set for any
>other I/O.

Sorry I'm not entirely clear on the impact of REQ_POLLED in this context.
I searched that REQ_POLLED is set for request if polled in io_uring or
io_uring_cmd, but here we just judge the state of request_queue.

Do you mean making this judgment here may not be a good choice, because
it may affect other IO (by same path), and this change should be just
targeted at io_uring?