linux-kernel - Re: [RFC PATCH 00/86] Make the kernel preemptible

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Message-ID: <20231107190016.2da8c402@gandalf.local.home>
Date:   Tue, 7 Nov 2023 19:00:16 -0500
From:   Steven Rostedt <rostedt@...dmis.org>
To:     Ankur Arora <ankur.a.arora@...cle.com>
Cc:     linux-kernel@...r.kernel.org, tglx@...utronix.de,
        peterz@...radead.org, torvalds@...ux-foundation.org,
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        krypton@...ich-teichert.org, David.Laight@...LAB.COM,
        richard@....at, mjguzik@...il.com
Subject: Re: [RFC PATCH 00/86] Make the kernel preemptible

On Tue, 07 Nov 2023 15:43:40 -0800
Ankur Arora <ankur.a.arora@...cle.com> wrote:

> 
> The TIF_NEED_RESCHED flag is evaluated at all three of the preemption
> points. TIF_NEED_RESCHED_LAZY only needs to be evaluated at ret-to-user.
> 
>                   ret-to-user    ret-to-kernel    preempt_count()
> NEED_RESCHED_LAZY    Y              N                N
> NEED_RESCHED         Y              Y                Y
> 
> Based on how various preemption models set the flag they would cause
> preemption at:

I would change the above to say "set the NEED_SCHED flag", as "set the
flag" is still ambiguous. Or am I still misunderstanding the below table?

> 
>                   ret-to-user    ret-to-kernel    preempt_count()
> none                 Y              N                N
> voluntary            Y              Y                Y
> full                 Y              Y                Y
> 

-- Steve