IO-Uring Archive on lore.kernel.org
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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: Mon, 17 Feb 2020 13:09:20 +0100
Message-ID: <20200217120920.GQ14914@hirez.programming.kicks-ass.net> (raw)
In-Reply-To: <b8069e62-7ea4-c7f3-55a3-838241951068@kernel.dk>

On Fri, Feb 14, 2020 at 01:44:32PM -0700, Jens Axboe wrote:

I've not looked at git trees yet, but the below doesn't apply to
anything I have at hand.

Anyway, I think I can still make sense of it -- just a rename or two
seems to be missing.

A few notes on the below...

> diff --git a/include/linux/sched.h b/include/linux/sched.h
> index 04278493bf15..447b06c6bed0 100644
> --- a/include/linux/sched.h
> +++ b/include/linux/sched.h
> @@ -685,6 +685,11 @@ struct task_struct {
>  #endif
>  	struct sched_dl_entity		dl;
>  
> +#ifdef CONFIG_IO_URING
> +	struct list_head		uring_work;
> +	raw_spinlock_t			uring_lock;
> +#endif
> +

Could we pretty please use struct callback_head for this, just like
task_work() and RCU ? Look at task_work_add() for inspiration.

And maybe remove the uring naming form this.

>  #ifdef CONFIG_UCLAMP_TASK
>  	/* Clamp values requested for a scheduling entity */
>  	struct uclamp_se		uclamp_req[UCLAMP_CNT];
> diff --git a/kernel/sched/core.c b/kernel/sched/core.c
> index 51ca491d99ed..170fefa1caf8 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
> @@ -4104,6 +4109,20 @@ void __noreturn do_task_dead(void)
>  		cpu_relax();
>  }
>  
> +#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 void sched_out_update(struct task_struct *tsk)
>  {
>  	/*
> @@ -4121,6 +4140,7 @@ static void sched_out_update(struct task_struct *tsk)
>  			io_wq_worker_sleeping(tsk);
>  		preempt_enable_no_resched();
>  	}
> +	io_uring_handler(tsk);
>  }
>  
>  static void sched_in_update(struct task_struct *tsk)
> @@ -4131,6 +4151,7 @@ static void sched_in_update(struct task_struct *tsk)
>  		else
>  			io_wq_worker_running(tsk);
>  	}
> +	io_uring_handler(tsk);
>  }

The problem I have here is that we have an unconditional load of the
cacheline that has ->uring_work in.

/me curses about how nobody seems interested in building useful
cacheline analyis tools :/

Lemme see if I can find a spot for this... perhaps something like so?



diff --git a/include/linux/sched.h b/include/linux/sched.h
index 0918904c939d..4fba93293fa1 100644
--- a/include/linux/sched.h
+++ b/include/linux/sched.h
@@ -649,6 +649,7 @@ struct task_struct {
 	/* Per task flags (PF_*), defined further below: */
 	unsigned int			flags;
 	unsigned int			ptrace;
+	int				on_rq;
 
 #ifdef CONFIG_SMP
 	struct llist_node		wake_entry;
@@ -671,14 +672,16 @@ struct task_struct {
 	int				recent_used_cpu;
 	int				wake_cpu;
 #endif
-	int				on_rq;
 
 	int				prio;
 	int				static_prio;
 	int				normal_prio;
 	unsigned int			rt_priority;
 
+	struct callbach_head		*sched_work;
+
 	const struct sched_class	*sched_class;
+
 	struct sched_entity		se;
 	struct sched_rt_entity		rt;
 #ifdef CONFIG_CGROUP_SCHED



  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
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 [this message]
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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