linux-kernel - Re: [PATCH v3 3/5] sched/fair: Switch to task based throttle model

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Message-ID: <20250716112735.GT1613200@noisy.programming.kicks-ass.net>
Date: Wed, 16 Jul 2025 13:27:35 +0200
From: Peter Zijlstra <peterz@...radead.org>
To: Aaron Lu <ziqianlu@...edance.com>
Cc: kernel test robot <lkp@...el.com>,
	Valentin Schneider <vschneid@...hat.com>,
	Ben Segall <bsegall@...gle.com>,
	K Prateek Nayak <kprateek.nayak@....com>,
	Chengming Zhou <chengming.zhou@...ux.dev>,
	Josh Don <joshdon@...gle.com>, Ingo Molnar <mingo@...hat.com>,
	Vincent Guittot <vincent.guittot@...aro.org>,
	Xi Wang <xii@...gle.com>, llvm@...ts.linux.dev,
	oe-kbuild-all@...ts.linux.dev, linux-kernel@...r.kernel.org,
	Juri Lelli <juri.lelli@...hat.com>,
	Dietmar Eggemann <dietmar.eggemann@....com>,
	Steven Rostedt <rostedt@...dmis.org>, Mel Gorman <mgorman@...e.de>,
	Chuyi Zhou <zhouchuyi@...edance.com>,
	Jan Kiszka <jan.kiszka@...mens.com>,
	Florian Bezdeka <florian.bezdeka@...mens.com>,
	Songtang Liu <liusongtang@...edance.com>
Subject: Re: [PATCH v3 3/5] sched/fair: Switch to task based throttle model

On Wed, Jul 16, 2025 at 02:57:07PM +0800, Aaron Lu wrote:
> On Wed, Jul 16, 2025 at 07:29:37AM +0800, kernel test robot wrote:
> > Hi Aaron,
> > 
> > kernel test robot noticed the following build warnings:
> > 
> > [auto build test WARNING on tip/sched/core]
> > [also build test WARNING on next-20250715]
> > [cannot apply to linus/master v6.16-rc6]
> > [If your patch is applied to the wrong git tree, kindly drop us a note.
> > And when submitting patch, we suggest to use '--base' as documented in
> > https://git-scm.com/docs/git-format-patch#_base_tree_information]
> > 
> > url:    https://github.com/intel-lab-lkp/linux/commits/Aaron-Lu/sched-fair-Add-related-data-structure-for-task-based-throttle/20250715-152307
> > base:   tip/sched/core
> > patch link:    https://lore.kernel.org/r/20250715071658.267-4-ziqianlu%40bytedance.com
> > patch subject: [PATCH v3 3/5] sched/fair: Switch to task based throttle model
> > config: i386-buildonly-randconfig-006-20250716 (https://download.01.org/0day-ci/archive/20250716/202507160730.0cXkgs0S-lkp@intel.com/config)
> > compiler: clang version 20.1.8 (https://github.com/llvm/llvm-project 87f0227cb60147a26a1eeb4fb06e3b505e9c7261)
> > reproduce (this is a W=1 build): (https://download.01.org/0day-ci/archive/20250716/202507160730.0cXkgs0S-lkp@intel.com/reproduce)
> > 
> > If you fix the issue in a separate patch/commit (i.e. not just a new version of
> > the same patch/commit), kindly add following tags
> > | Reported-by: kernel test robot <lkp@...el.com>
> > | Closes: https://lore.kernel.org/oe-kbuild-all/202507160730.0cXkgs0S-lkp@intel.com/
> > 
> > All warnings (new ones prefixed by >>):
> > 
> > >> kernel/sched/fair.c:5456:33: warning: implicit truncation from 'int' to a one-bit wide bit-field changes value from 1 to -1 [-Wsingle-bit-bitfield-constant-conversion]
> >     5456 |                         cfs_rq->pelt_clock_throttled = 1;
> >          |                                                      ^ ~

Nice warning from clang.

> 
> Thanks for the report.
> 
> I don't think this will affect correctness since both cfs_rq's throttled
> and pelt_clock_throttled fields are used as true(not 0) or false(0). I
> used bitfield for them to save some space.
> 
> Change their types to either unsigned int or bool should cure this
> warning, I suppose bool looks more clear?
> 
> diff --git a/kernel/sched/sched.h b/kernel/sched/sched.h
> index dbe52e18b93a0..434f816a56701 100644
> --- a/kernel/sched/sched.h
> +++ b/kernel/sched/sched.h
> @@ -737,8 +737,8 @@ struct cfs_rq {
>  	u64			throttled_clock_pelt_time;
>  	u64			throttled_clock_self;
>  	u64			throttled_clock_self_time;
> -	int			throttled:1;
> -	int			pelt_clock_throttled:1;
> +	bool			throttled:1;
> +	bool			pelt_clock_throttled:1;
>  	int			throttle_count;
>  	struct list_head	throttled_list;
>  	struct list_head	throttled_csd_list;

Yeah, either this or any unsigned type will do.