public inbox for [email protected]
 help / color / mirror / Atom feed
From: Jens Axboe <[email protected]>
To: Peter Zijlstra <[email protected]>
Cc: "Carter Li 李通洲" <[email protected]>,
	"Pavel Begunkov" <[email protected]>,
	io-uring <[email protected]>
Subject: Re: [ISSUE] The time cost of IOSQE_IO_LINK
Date: Mon, 17 Feb 2020 08:12:30 -0800	[thread overview]
Message-ID: <[email protected]> (raw)
In-Reply-To: <[email protected]>

On 2/17/20 5:09 AM, Peter Zijlstra wrote:
> 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...

Thanks for continuing to look at it, while we both try and make sense of
it :-)

>> 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.

Sure, so add a new one, sched_work, and have it get this sched-in or
sched-out behavior.

Only potential hitch I see there is related to ordering, which is more
of a fairness thab correctness issue. I'm going to ignore that for now,
and we can always revisit later.

> And maybe remove the uring naming form this.

No problem

>>  #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

Thanks, I'll kick off the series with doing it based on this instead.

-- 
Jens Axboe


  reply	other threads:[~2020-02-17 16:13 UTC|newest]

Thread overview: 59+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2020-02-12 16:31 [ISSUE] The time cost of IOSQE_IO_LINK 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
2020-02-17 16:12                             ` Jens Axboe [this message]
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

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 \
    [email protected] \
    [email protected] \
    [email protected] \
    [email protected] \
    [email protected] \
    [email protected] \
    /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
Be sure your reply has a Subject: header at the top and a blank line before the message body.
This is a public inbox, see mirroring instructions
for how to clone and mirror all data and code used for this inbox