From: Jens Axboe <axboe@kernel.dk> To: Peter Zijlstra <peterz@infradead.org> 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 08:47:56 -0700 Message-ID: <5995f84e-8a6c-e774-6bb5-5b9b87a9cd3c@kernel.dk> (raw) In-Reply-To: <20200214153218.GM14914@hirez.programming.kicks-ass.net> On 2/14/20 8:32 AM, Peter Zijlstra wrote: > 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. Probably not ;-) >> 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? Let me try and clarify - this isn't for the worker tasks, this is for any task that is using io_uring. In fact, it's particularly not for the worker threads, just the task itself. I basically want the handler to be called when: 1) The task is scheduled in. The poll will complete and stuff some items on that task list, and I want to task to process them as it wakes up. 2) The task is going to sleep, don't want to leave entries around while the task is sleeping. 3) I need it to be called from "normal" context, with ints enabled, preempt enabled, etc. sched_update_worker() (with a rename) looks ideal for #1, and the context is sane for me. Just need a good spot to put the hook call for schedule out. I think this: if (tsk->flags & (PF_WQ_WORKER | PF_IO_WORKER)) { preempt_disable(); if (tsk->flags & PF_WQ_WORKER) wq_worker_sleeping(tsk); else io_wq_worker_sleeping(tsk); preempt_enable_no_resched(); } just needs to go into another helper, and then I can call it there outside of the preempt. I'm sure there are daemons lurking here, but I'll test and see how it goes... -- Jens Axboe
next prev parent reply index Thread overview: 59+ 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 2020-02-14 15:47 ` Jens Axboe [this message] 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 2020-02-28 19:17 ` Jens Axboe 2020-02-28 19:25 ` Peter Zijlstra 2020-02-28 19:28 ` Jens Axboe 2020-02-28 20:06 ` Peter Zijlstra 2020-02-28 20:15 ` 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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