linux-kernel - Re: [PATCH] kthread: Add kthread

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Date:   Mon, 12 Oct 2020 08:14:50 -0700
From:   Rob Clark <robdclark@...omium.org>
To:     Steven Rostedt <rostedt@...dmis.org>
Cc:     Rob Clark <robdclark@...il.com>,
        LKML <linux-kernel@...r.kernel.org>,
        Ingo Molnar <mingo@...hat.com>,
        "Peter Zijlstra (Intel)" <peterz@...radead.org>,
        Phil Auld <pauld@...hat.com>,
        Valentin Schneider <valentin.schneider@....com>,
        Thara Gopinath <thara.gopinath@...aro.org>,
        Randy Dunlap <rdunlap@...radead.org>,
        Vincent Donnefort <vincent.donnefort@....com>,
        Mel Gorman <mgorman@...hsingularity.net>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Jens Axboe <axboe@...nel.dk>,
        Marcelo Tosatti <mtosatti@...hat.com>,
        Frederic Weisbecker <frederic@...nel.org>,
        Ilias Stamatis <stamatis.iliass@...il.com>,
        Liang Chen <cl@...k-chips.com>,
        Ben Dooks <ben.dooks@...ethink.co.uk>,
        Peter Zijlstra <a.p.zijlstra@...llo.nl>,
        "J. Bruce Fields" <bfields@...hat.com>
Subject: Re: [PATCH] kthread: Add kthread_work tracepoints

On Mon, Oct 12, 2020 at 6:59 AM Steven Rostedt <rostedt@...dmis.org> wrote:
>
> On Sat, 10 Oct 2020 11:03:22 -0700
> Rob Clark <robdclark@...il.com> wrote:
>
> > /**
> > + * sched_kthread_work_execute_start - called immediately before the work callback
> > + * @work:    pointer to struct kthread_work
> > + *
> > + * Allows to track kthread work execution.
> > + */
> > +TRACE_EVENT(sched_kthread_work_execute_start,
> > +
> > +     TP_PROTO(struct kthread_work *work),
> > +
> > +     TP_ARGS(work),
> > +
> > +     TP_STRUCT__entry(
> > +             __field( void *,        work    )
> > +             __field( void *,        function)
> > +     ),
> > +
> > +     TP_fast_assign(
> > +             __entry->work           = work;
> > +             __entry->function       = work->func;
> > +     ),
> > +
> > +     TP_printk("work struct %p: function %ps", __entry->work, __entry->function)
> > +);
> > +
> > +/**
> > + * sched_kthread_work_execute_end - called immediately after the work callback
> > + * @work:    pointer to struct work_struct
> > + * @function:   pointer to worker function
> > + *
> > + * Allows to track workqueue execution.
> > + */
> > +TRACE_EVENT(sched_kthread_work_execute_end,
> > +
> > +     TP_PROTO(struct kthread_work *work, kthread_work_func_t function),
> > +
> > +     TP_ARGS(work, function),
> > +
> > +     TP_STRUCT__entry(
> > +             __field( void *,        work    )
> > +             __field( void *,        function)
> > +     ),
> > +
> > +     TP_fast_assign(
> > +             __entry->work           = work;
> > +             __entry->function       = function;
> > +     ),
> > +
> > +     TP_printk("work struct %p: function %ps", __entry->work, __entry->function)
> > +);
> > +
>
>
> Please combine the above into:
>
> DECLARE_EVENT_CLASS(sched_kthread_work_execute_template,
>
>         TP_PROTO(struct kthread_work *work),
>
>         TP_ARGS(work),
>
>         TP_STRUCT__entry(
>                 __field( void *,        work    )
>                 __field( void *,        function)
>         ),
>
>         TP_fast_assign(
>                 __entry->work           = work;
>                 __entry->function       = work->func;
>         ),
>
>         TP_printk("work struct %p: function %ps", __entry->work, __entry->function)
> );
>
> DEFINE_EVENT(sched_kthread_work_execute_template, sched_kthread_work_execute_start,
>         TP_PROTO(struct kthread_work *work),
>         TP_ARGS(work));
>
> DEFINE_EVENT(sched_kthread_work_execute_template, sched_kthread_work_execute_end,
>         TP_PROTO(struct kthread_work *work),
>         TP_ARGS(work));
>
> As events are cheap, classes are expensive (size wise), and a TRACE_EVENT()
> is really just a CLASS and EVENT for a single instance.

I think we cannot quite do this, because we should not rely on being
able to dereference work after it finishes.  Although I suppose I
could just define it to explicitly pass the fxn ptr to both
tracepoints..

BR,
-R