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From: Peter Zijlstra <peterz@infradead.org>
To: Jens Axboe <axboe@kernel.dk>
Cc: "Carter Li 李通洲" <carter.li@eoitek.com>,
	"Pavel Begunkov" <asml.silence@gmail.com>,
	io-uring <io-uring@vger.kernel.org>
Subject: Re: [ISSUE] The time cost of IOSQE_IO_LINK
Date: Fri, 14 Feb 2020 16:32:18 +0100
Message-ID: <20200214153218.GM14914@hirez.programming.kicks-ass.net> (raw)
In-Reply-To: <1b9a7390-7539-a8bc-d437-493253b13d77@kernel.dk>

On Thu, Feb 13, 2020 at 10:03:54PM -0700, Jens Axboe wrote:

> CC'ing peterz for some cluebat knowledge. Peter, is there a nice way to
> currently do something like this? Only thing I'm currently aware of is
> the preempt in/out notifiers, but they don't quite provide what I need,
> since I need to pass some data (a request) as well.

Whee, nothing quite like this around I think.

> The full detail on what I'm trying here is:
> 
> io_uring can have linked requests. One obvious use case for that is to
> queue a POLLIN on a socket, and then link a read/recv to that. When the
> poll completes, we want to run the read/recv. io_uring hooks into the
> waitqueue wakeup handler to finish the poll request, and since we're
> deep in waitqueue wakeup code, it queues the linked read/recv for
> execution via an async thread. This is not optimal, obviously, as it
> relies on a switch to a new thread to perform this read. This hack
> queues a backlog to the task itself, and runs it when it's scheduled in.
> Probably want to do the same for sched out as well, currently I just
> hack that in the io_uring wait part...

I'll definitely need to think more about this, but a few comments on the
below.

> +static void __io_uring_task_handler(struct list_head *list)
> +{
> +	struct io_kiocb *req;
> +
> +	while (!list_empty(list)) {
> +		req = list_first_entry(list, struct io_kiocb, list);
> +		list_del(&req->list);
> +
> +		__io_queue_sqe(req, NULL);
> +	}
> +}
> +
> +void io_uring_task_handler(struct task_struct *tsk)
> +{
> +	LIST_HEAD(list);
> +
> +	raw_spin_lock_irq(&tsk->uring_lock);
> +	if (!list_empty(&tsk->uring_work))
> +		list_splice_init(&tsk->uring_work, &list);
> +	raw_spin_unlock_irq(&tsk->uring_lock);
> +
> +	__io_uring_task_handler(&list);
> +}

> diff --git a/kernel/sched/core.c b/kernel/sched/core.c
> index fc1dfc007604..b60f081cac17 100644
> --- a/kernel/sched/core.c
> +++ b/kernel/sched/core.c
> @@ -2717,6 +2717,11 @@ static void __sched_fork(unsigned long clone_flags, struct task_struct *p)
>  	INIT_HLIST_HEAD(&p->preempt_notifiers);
>  #endif
>  
> +#ifdef CONFIG_IO_URING
> +	INIT_LIST_HEAD(&p->uring_work);
> +	raw_spin_lock_init(&p->uring_lock);
> +#endif
> +
>  #ifdef CONFIG_COMPACTION
>  	p->capture_control = NULL;
>  #endif
> @@ -3069,6 +3074,20 @@ fire_sched_out_preempt_notifiers(struct task_struct *curr,
>  
>  #endif /* CONFIG_PREEMPT_NOTIFIERS */
>  
> +#ifdef CONFIG_IO_URING
> +extern void io_uring_task_handler(struct task_struct *tsk);
> +
> +static inline void io_uring_handler(struct task_struct *tsk)
> +{
> +	if (!list_empty(&tsk->uring_work))
> +		io_uring_task_handler(tsk);
> +}
> +#else /* !CONFIG_IO_URING */
> +static inline void io_uring_handler(struct task_struct *tsk)
> +{
> +}
> +#endif
> +
>  static inline void prepare_task(struct task_struct *next)
>  {
>  #ifdef CONFIG_SMP
> @@ -3322,6 +3341,8 @@ asmlinkage __visible void schedule_tail(struct task_struct *prev)
>  	balance_callback(rq);
>  	preempt_enable();
>  
> +	io_uring_handler(current);
> +
>  	if (current->set_child_tid)
>  		put_user(task_pid_vnr(current), current->set_child_tid);
>  

I suspect you meant to put that in finish_task_switch() which is the
tail end of every schedule(), schedule_tail() is the tail end of
clone().

Or maybe you meant to put it in (and rename) sched_update_worker() which
is after every schedule() but in a preemptible context -- much saner
since you don't want to go add an unbounded amount of work in a
non-preemptible context.

At which point you already have your callback: io_wq_worker_running(),
or is this for any random task?



  reply index

Thread overview: 54+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2020-02-12 16:31 Carter Li 李通洲
2020-02-12 17:11 ` Jens Axboe
2020-02-12 17:22   ` Jens Axboe
2020-02-12 17:29     ` Jens Axboe
2020-02-13  0:33   ` Carter Li 李通洲
2020-02-13 15:08     ` Pavel Begunkov
2020-02-13 15:14       ` Jens Axboe
2020-02-13 15:51         ` Carter Li 李通洲
2020-02-14  1:25           ` Carter Li 李通洲
2020-02-14  2:45             ` Jens Axboe
2020-02-14  5:03               ` Jens Axboe
2020-02-14 15:32                 ` Peter Zijlstra [this message]
2020-02-14 15:47                   ` Jens Axboe
2020-02-14 16:18                     ` Jens Axboe
2020-02-14 17:52                       ` Jens Axboe
2020-02-14 20:44                         ` Jens Axboe
2020-02-15  0:16                           ` Carter Li 李通洲
2020-02-15  1:10                             ` Jens Axboe
2020-02-15  1:25                               ` Carter Li 李通洲
2020-02-15  1:27                                 ` Jens Axboe
2020-02-15  6:01                                   ` Jens Axboe
2020-02-15  6:32                                     ` Carter Li 李通洲
2020-02-15 15:11                                       ` Jens Axboe
2020-02-16 19:06                                     ` Pavel Begunkov
2020-02-16 22:23                                       ` Jens Axboe
2020-02-17 10:30                                         ` Pavel Begunkov
2020-02-17 19:30                                           ` Jens Axboe
2020-02-16 23:06                                       ` Jens Axboe
2020-02-16 23:07                                         ` Jens Axboe
2020-02-17 12:09                           ` Peter Zijlstra
2020-02-17 16:12                             ` Jens Axboe
2020-02-17 17:16                               ` Jens Axboe
2020-02-17 17:46                                 ` Peter Zijlstra
2020-02-17 18:16                                   ` Jens Axboe
2020-02-18 13:13                                     ` Peter Zijlstra
2020-02-18 14:27                                       ` [PATCH] asm-generic/atomic: Add try_cmpxchg() fallbacks Peter Zijlstra
2020-02-18 14:40                                         ` Peter Zijlstra
2020-02-20 10:30                                         ` Will Deacon
2020-02-20 10:37                                           ` Peter Zijlstra
2020-02-20 10:39                                             ` Will Deacon
2020-02-18 14:56                                       ` [ISSUE] The time cost of IOSQE_IO_LINK Oleg Nesterov
2020-02-18 15:07                                         ` Oleg Nesterov
2020-02-18 15:38                                           ` Peter Zijlstra
2020-02-18 16:33                                             ` Jens Axboe
2020-02-18 15:07                                         ` Peter Zijlstra
2020-02-18 15:50                                           ` [PATCH] task_work_run: don't take ->pi_lock unconditionally Oleg Nesterov
2020-02-20 16:39                                             ` Peter Zijlstra
2020-02-20 17:22                                               ` Oleg Nesterov
2020-02-20 17:49                                                 ` Peter Zijlstra
2020-02-21 14:52                                                   ` Oleg Nesterov
2020-02-24 18:47                                                     ` Jens Axboe
2020-02-18 16:46                                       ` [ISSUE] The time cost of IOSQE_IO_LINK Jens Axboe
2020-02-18 16:52                                         ` Jens Axboe
2020-02-18 13:13                               ` Peter Zijlstra

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