lkml.org 
[lkml]   [2020]   [May]   [20]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
/
SubjectRe: io_uring vs CPU hotplug, was Re: [PATCH 5/9] blk-mq: don't set data->ctx and data->hctx in blk_mq_alloc_request_hctx
From
Date
On 5/20/20 1:41 PM, Thomas Gleixner wrote:
> Jens Axboe <axboe@kernel.dk> writes:
>> On 5/20/20 8:45 AM, Jens Axboe wrote:
>>> It just uses kthread_create_on_cpu(), nothing home grown. Pretty sure
>>> they just break affinity if that CPU goes offline.
>>
>> Just checked, and it works fine for me. If I create an SQPOLL ring with
>> SQ_AFF set and bound to CPU 3, if CPU 3 goes offline, then the kthread
>> just appears unbound but runs just fine. When CPU 3 comes online again,
>> the mask appears correct.
>
> When exactly during the unplug operation is it unbound?

When the CPU has been fully offlined. I check the affinity mask, it
reports 0. But it's still being scheduled, and it's processing work.
Here's an example, PID 420 is the thread in question:

[root@archlinux cpu3]# taskset -p 420
pid 420's current affinity mask: 8
[root@archlinux cpu3]# echo 0 > online
[root@archlinux cpu3]# taskset -p 420
pid 420's current affinity mask: 0
[root@archlinux cpu3]# echo 1 > online
[root@archlinux cpu3]# taskset -p 420
pid 420's current affinity mask: 8

So as far as I can tell, it's working fine for me with the goals
I have for that kthread.

--
Jens Axboe

\
 
 \ /
  Last update: 2020-05-20 22:19    [W:0.066 / U:0.140 seconds]
©2003-2020 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site