linux-kernel - Re: [PATCH v2 08/35] entry: handle lazy rescheduling at user-exit

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Message-ID: <20240528161231.GD26599@noisy.programming.kicks-ass.net>
Date: Tue, 28 May 2024 18:12:31 +0200
From: Peter Zijlstra <peterz@...radead.org>
To: Ankur Arora <ankur.a.arora@...cle.com>
Cc: linux-kernel@...r.kernel.org, tglx@...utronix.de,
	torvalds@...ux-foundation.org, paulmck@...nel.org,
	rostedt@...dmis.org, mark.rutland@....com, juri.lelli@...hat.com,
	joel@...lfernandes.org, raghavendra.kt@....com,
	sshegde@...ux.ibm.com, boris.ostrovsky@...cle.com,
	konrad.wilk@...cle.com, Andy Lutomirski <luto@...nel.org>
Subject: Re: [PATCH v2 08/35] entry: handle lazy rescheduling at user-exit

On Mon, May 27, 2024 at 05:34:54PM -0700, Ankur Arora wrote:
> The scheduling policy for TIF_NEED_RESCHED_LAZY is to allow the
> running task to voluntarily schedule out, running it to completion.
> 
> For archs with GENERIC_ENTRY, do this by adding a check in
> exit_to_user_mode_loop().
> 
> Cc: Peter Zijlstra <peterz@...radead.org>
> Cc: Andy Lutomirski <luto@...nel.org>
> Originally-by: Thomas Gleixner <tglx@...utronix.de>
> Link: https://lore.kernel.org/lkml/87jzshhexi.ffs@tglx/
> Signed-off-by: Ankur Arora <ankur.a.arora@...cle.com>
> ---
>  include/linux/entry-common.h | 2 +-
>  kernel/entry/common.c        | 2 +-
>  2 files changed, 2 insertions(+), 2 deletions(-)
> 
> diff --git a/include/linux/entry-common.h b/include/linux/entry-common.h
> index b0fb775a600d..f5bb19369973 100644
> --- a/include/linux/entry-common.h
> +++ b/include/linux/entry-common.h
> @@ -65,7 +65,7 @@
>  #define EXIT_TO_USER_MODE_WORK						\
>  	(_TIF_SIGPENDING | _TIF_NOTIFY_RESUME | _TIF_UPROBE |		\
>  	 _TIF_NEED_RESCHED | _TIF_PATCH_PENDING | _TIF_NOTIFY_SIGNAL |	\
> -	 ARCH_EXIT_TO_USER_MODE_WORK)
> +	 _TIF_NEED_RESCHED_LAZY | ARCH_EXIT_TO_USER_MODE_WORK)

Should we be wanting both TIF_NEED_RESCHED flags side-by-side?