io-uring.vger.kernel.org archive mirror
 help / color / mirror / Atom feed
From: Hao Xu <haoxu@linux.alibaba.com>
To: Tejun Heo <tj@kernel.org>
Cc: Jens Axboe <axboe@kernel.dk>, Zefan Li <lizefan.x@bytedance.com>,
	Johannes Weiner <hannes@cmpxchg.org>,
	Pavel Begunkov <asml.silence@gmail.com>,
	io-uring@vger.kernel.org, cgroups@vger.kernel.org,
	Joseph Qi <joseph.qi@linux.alibaba.com>
Subject: Re: [PATCH 2/2] io_uring: consider cgroup setting when binding sqpoll cpu
Date: Fri, 3 Sep 2021 23:04:07 +0800	[thread overview]
Message-ID: <c49d9b26-1c74-316a-c933-e6964695a286@linux.alibaba.com> (raw)
In-Reply-To: <YS+tPq1eiQLx4P3M@slm.duckdns.org>

在 2021/9/2 上午12:41, Tejun Heo 写道:
Hi Tejun,
> Hello,
> 
> On Wed, Sep 01, 2021 at 08:43:22PM +0800, Hao Xu wrote:
>> @@ -7112,11 +7113,9 @@ static int io_sq_thread(void *data)
>>   
>>   	snprintf(buf, sizeof(buf), "iou-sqp-%d", sqd->task_pid);
>>   	set_task_comm(current, buf);
>> +	if (sqd->sq_cpu != -1 && test_cpu_in_current_cpuset(sqd->sq_cpu))
>>   		set_cpus_allowed_ptr(current, cpumask_of(sqd->sq_cpu));
>> +
> 
> Would it make sense to just test whether set_cpus_allowed_ptr() succeeded
> afterwards?
Do you mean: if (sqd->sq_cpu != -1 && !set_cpus_allowed_ptr(current, 
cpumask_of(sqd->sq_cpu)))

I'm not familiar with set_cpus_allowed_ptr(), you mean it contains the
similar logic of test_cpu_in_current_cpuset?
> 
>> @@ -8310,8 +8309,10 @@ static int io_sq_offload_create(struct io_ring_ctx *ctx,
>>   			int cpu = p->sq_thread_cpu;
>>   
>>   			ret = -EINVAL;
>> -			if (cpu >= nr_cpu_ids || !cpu_online(cpu))
>> +			if (cpu >= nr_cpu_ids || !cpu_online(cpu) ||
>> +			    !test_cpu_in_current_cpuset(cpu))
>>   				goto err_sqpoll;
>> +
> 
> Failing operations on transient conditions like this may be confusing. Let's
> ignore cpuset for now. CPU hotplug is sometimes driven automatically for
> power saving purposes, so failing operation based on whether a cpu is online
> means that the success or failure of the operation can seem arbitrary. If
> the operation takes place while the cpu happens to be online, it succeeds
> and the thread gets unbound and rebound automatically as the cpu goes
This is a bit beyond of my knowledge, so you mean if the cpu back
online, the task will automatically schedule to this cpu? if it's true,
I think the code logic here is fine.
> offline and online. If the operation takes place while the cpu happens to be
> offline, the operation fails.
It's ok that it fails, we leave the option of retry to users themselves.
> 
> I don't know what the intended behavior here should be and we haven't been
> pretty bad at defining reasonable behavior around cpu hotplug, so it'd
> probably be worthwhile to consider what the behavior should be.
> 
> Thanks.
> 
Thanks,
Hao


  parent reply	other threads:[~2021-09-03 15:04 UTC|newest]

Thread overview: 14+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2021-09-01 12:43 [PATCH v4 0/2] refactor sqthread cpu binding logic Hao Xu
2021-09-01 12:43 ` [PATCH 1/2] cpuset: add a helper to check if cpu in cpuset of current task Hao Xu
2021-09-01 12:43 ` [PATCH 2/2] io_uring: consider cgroup setting when binding sqpoll cpu Hao Xu
2021-09-01 16:41   ` Tejun Heo
2021-09-01 16:42     ` Tejun Heo
2021-09-03 15:04     ` Hao Xu [this message]
2021-09-07 16:54       ` Tejun Heo
2021-09-07 19:28         ` Hao Xu
2021-09-02 16:48 ` [PATCH v4 0/2] refactor sqthread cpu binding logic Michal Koutný
2021-09-02 18:00   ` Jens Axboe
2021-09-09 12:34     ` Michal Koutný
2021-09-03 14:43   ` Hao Xu
  -- strict thread matches above, loose matches on Subject: below --
2021-09-01 10:18 [PATCH v3 " Hao Xu
2021-09-01 10:18 ` [PATCH 2/2] io_uring: consider cgroup setting when binding sqpoll cpu Hao Xu
2021-09-01 12:31   ` Hao Xu

Reply instructions:

You may reply publicly to this message via plain-text email
using any one of the following methods:

* Save the following mbox file, import it into your mail client,
  and reply-to-all from there: mbox

  Avoid top-posting and favor interleaved quoting:
  https://en.wikipedia.org/wiki/Posting_style#Interleaved_style

* Reply using the --to, --cc, and --in-reply-to
  switches of git-send-email(1):

  git send-email \
    --in-reply-to=c49d9b26-1c74-316a-c933-e6964695a286@linux.alibaba.com \
    --to=haoxu@linux.alibaba.com \
    --cc=asml.silence@gmail.com \
    --cc=axboe@kernel.dk \
    --cc=cgroups@vger.kernel.org \
    --cc=hannes@cmpxchg.org \
    --cc=io-uring@vger.kernel.org \
    --cc=joseph.qi@linux.alibaba.com \
    --cc=lizefan.x@bytedance.com \
    --cc=tj@kernel.org \
    --subject='Re: [PATCH 2/2] io_uring: consider cgroup setting when binding sqpoll cpu' \
    /path/to/YOUR_REPLY

  https://kernel.org/pub/software/scm/git/docs/git-send-email.html

* If your mail client supports setting the In-Reply-To header
  via mailto: links, try the mailto: link

This is a public inbox, see mirroring instructions
for how to clone and mirror all data and code used for this inbox;
as well as URLs for NNTP newsgroup(s).