Re: [PATCH 2/2] io_uring: use TWA_SIGNAL for task_work if the task isn't running

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On 8/10/20 3:26 PM, Jann Horn wrote:
> On Mon, Aug 10, 2020 at 11:12 PM Jens Axboe <axboe@xxxxxxxxx> wrote:
>> On 8/10/20 3:10 PM, Peter Zijlstra wrote:
>>> On Mon, Aug 10, 2020 at 03:06:49PM -0600, Jens Axboe wrote:
>>>
>>>> should work as far as I can tell, but I don't even know if there's a
>>>> reliable way to do task_in_kernel().
>>>
>>> Only on NOHZ_FULL, and tracking that is one of the things that makes it
>>> so horribly expensive.
>>
>> Probably no other way than to bite the bullet and just use TWA_SIGNAL
>> unconditionally...
> 
> Why are you trying to avoid using TWA_SIGNAL? Is there a specific part
> of handling it that's particularly slow?

Not particularly slow, but it's definitely heavier than TWA_RESUME. And
as we're driving any pollable async IO through this, just trying to
ensure it's as light as possible.

It's not a functional thing, just efficiency.

-- 
Jens Axboe




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