From: Tejun Heo <tj@kernel.org> To: Hao Xu <haoxu@linux.alibaba.com> 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: Wed, 1 Sep 2021 06:41:34 -1000 [thread overview] Message-ID: <YS+tPq1eiQLx4P3M@slm.duckdns.org> (raw) In-Reply-To: <20210901124322.164238-3-haoxu@linux.alibaba.com> 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? > @@ -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 offline and online. If the operation takes place while the cpu happens to be offline, the operation fails. 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. -- tejun
WARNING: multiple messages have this Message-ID (diff)
From: Tejun Heo <tj-DgEjT+Ai2ygdnm+yROfE0A@public.gmane.org> To: Hao Xu <haoxu-KPsoFbNs7GizrGE5bRqYAgC/G2K4zDHf@public.gmane.org> Cc: Jens Axboe <axboe-tSWWG44O7X1aa/9Udqfwiw@public.gmane.org>, Zefan Li <lizefan.x-EC8Uxl6Npydl57MIdRCFDg@public.gmane.org>, Johannes Weiner <hannes-druUgvl0LCNAfugRpC6u6w@public.gmane.org>, Pavel Begunkov <asml.silence-Re5JQEeQqe8AvxtiuMwx3w@public.gmane.org>, io-uring-u79uwXL29TY76Z2rM5mHXA@public.gmane.org, cgroups-u79uwXL29TY76Z2rM5mHXA@public.gmane.org, Joseph Qi <joseph.qi-KPsoFbNs7GizrGE5bRqYAgC/G2K4zDHf@public.gmane.org> Subject: Re: [PATCH 2/2] io_uring: consider cgroup setting when binding sqpoll cpu Date: Wed, 1 Sep 2021 06:41:34 -1000 [thread overview] Message-ID: <YS+tPq1eiQLx4P3M@slm.duckdns.org> (raw) In-Reply-To: <20210901124322.164238-3-haoxu-KPsoFbNs7GizrGE5bRqYAgC/G2K4zDHf@public.gmane.org> 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? > @@ -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 offline and online. If the operation takes place while the cpu happens to be offline, the operation fails. 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. -- tejun
next prev parent reply other threads:[~2021-09-01 16:41 UTC|newest] Thread overview: 23+ 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 ` Hao Xu 2021-09-01 12:43 ` [PATCH 2/2] io_uring: consider cgroup setting when binding sqpoll cpu Hao Xu 2021-09-01 12:43 ` Hao Xu 2021-09-01 16:41 ` Tejun Heo [this message] 2021-09-01 16:41 ` Tejun Heo 2021-09-01 16:42 ` Tejun Heo 2021-09-03 15:04 ` Hao Xu 2021-09-03 15:04 ` Hao Xu 2021-09-07 16:54 ` Tejun Heo 2021-09-07 16:54 ` Tejun Heo 2021-09-07 19:28 ` Hao Xu 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 2021-09-02 18:00 ` Jens Axboe 2021-09-09 12:34 ` Michal Koutný 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 10:18 ` Hao Xu 2021-09-01 12:31 ` Hao Xu
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