linux-kernel - Re: [RFC][PATCH v2 10/10] irq

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Date:   Tue, 18 Aug 2020 08:52:38 -0700
From:   Randy Dunlap <rdunlap@...radead.org>
To:     Peter Zijlstra <peterz@...radead.org>, mingo@...nel.org,
        torvalds@...ux-foundation.org
Cc:     linux-kernel@...r.kernel.org, will@...nel.org, paulmck@...nel.org,
        hch@....de, axboe@...nel.dk, chris@...is-wilson.co.uk,
        davem@...emloft.net, kuba@...nel.org, fweisbec@...il.com,
        oleg@...hat.com, vincent.guittot@...aro.org
Subject: Re: [RFC][PATCH v2 10/10] irq_work: Add a few comments

Hi Peter,

a few typos below...

On 8/18/20 3:51 AM, Peter Zijlstra wrote:
> 
> Signed-off-by: Peter Zijlstra (Intel) <peterz@...radead.org>
> ---
>  include/linux/irq_work.h |   80 +++++++++++++++++++++++++++++++++++++++++------
>  kernel/irq_work.c        |   10 +++++
>  2 files changed, 80 insertions(+), 10 deletions(-)
> 
> --- a/include/linux/irq_work.h
> +++ b/include/linux/irq_work.h


> @@ -48,12 +47,45 @@ static inline bool irq_work_is_busy(stru
>  
>  #ifdef CONFIG_IRQ_WORK
>  
> +/*
> + * irq_work_queue(): run @work in IRQ context on this CPU
> + * @work: work to run
> + *
> + * Self-IPI, NMI-safe
> + *
> + * When the function returns false; @work is already queued and
> + * any eventual execution of it's func() is guaranteed to see

                                its

> + * any state before the failing enqueue.
> + */
>  bool irq_work_queue(struct irq_work *work);
> +
> +/*
> + * irq_work_queue_on(): run @work in IRQ context on @cpu
> + * @work: work to run
> + * @cpu: cpu to run @work on
> + *
> + * *NOT* NMI-safe
> + *
> + * When the function returns false; @work is already queued and

                                false,

> + * any eventual execution of it's func() is guaranteed to see

                                its

> + * any state before the failing enqueue.
> + */

> @@ -67,8 +99,36 @@ static inline bool irq_work_needs_cpu(vo

> +/*
> + * irq_work_queue_remote_state(): like irq_work_queue_remote() except dangerous
> + * @cpu:
> + * @work:
> + *
> + * DO NOT USE, this function is horrible/dangerous.
> + *
> + * The test-and-set-PENDING is not atomic, it also doesn't set
> + * the BUSY bit and with that breaks irq_work_sync().
> + *
> + * This means that the caller needs external serialization; life-time,
> + * where relevant, also needs to be externally orchestated.

                                                  orchestrated.

> + *
> + * There is no validation/debugging to help you if you get it wrong.
> + */
>  extern int irq_work_queue_remote_static(int cpu, struct irq_work *work);
> +
>  extern void irq_work_single(void *arg);
>  #endif
>  


-- 
~Randy