linux-kernel - Re: [PATCH v10 04/30] x86/resctrl: Optimize cpumask_any

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Message-ID: <aB4jHPsWVNqrSG6W@yury>
Date: Fri, 9 May 2025 11:45:32 -0400
From: Yury Norov <yury.norov@...il.com>
To: "Shaopeng Tan (Fujitsu)" <tan.shaopeng@...itsu.com>
Cc: 'James Morse' <james.morse@....com>, "x86@...nel.org" <x86@...nel.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	Reinette Chatre <reinette.chatre@...el.com>,
	Thomas Gleixner <tglx@...utronix.de>,
	Ingo Molnar <mingo@...hat.com>, Borislav Petkov <bp@...en8.de>,
	H Peter Anvin <hpa@...or.com>, Babu Moger <Babu.Moger@....com>,
	"shameerali.kolothum.thodi@...wei.com" <shameerali.kolothum.thodi@...wei.com>,
	D Scott Phillips OS <scott@...amperecomputing.com>,
	"carl@...amperecomputing.com" <carl@...amperecomputing.com>,
	"lcherian@...vell.com" <lcherian@...vell.com>,
	"bobo.shaobowang@...wei.com" <bobo.shaobowang@...wei.com>,
	"baolin.wang@...ux.alibaba.com" <baolin.wang@...ux.alibaba.com>,
	Jamie Iles <quic_jiles@...cinc.com>,
	Xin Hao <xhao@...ux.alibaba.com>,
	"peternewman@...gle.com" <peternewman@...gle.com>,
	"dfustini@...libre.com" <dfustini@...libre.com>,
	"amitsinght@...vell.com" <amitsinght@...vell.com>,
	David Hildenbrand <david@...hat.com>,
	Rex Nie <rex.nie@...uarmicro.com>,
	Dave Martin <dave.martin@....com>, Koba Ko <kobak@...dia.com>,
	Shanker Donthineni <sdonthineni@...dia.com>,
	"fenghuay@...dia.com" <fenghuay@...dia.com>
Subject: Re: [PATCH v10 04/30] x86/resctrl: Optimize
 cpumask_any_housekeeping()

On Fri, May 09, 2025 at 08:39:51AM +0000, Shaopeng Tan (Fujitsu) wrote:
> Hello James,
> 
> > From: "Yury Norov [NVIDIA]" <yury.norov@...il.com>
> > 
> > With the lack of cpumask_any_andnot_but(), cpumask_any_housekeeping()
> > has to abuse cpumask_nth() functions.
> > 
> > Update cpumask_any_housekeeping() to use the new cpumask_any_but()
> > and cpumask_any_andnot_but(). These two functions understand
> > RESCTRL_PICK_ANY_CPU, which simplifies cpumask_any_housekeeping()
> > significantly.
> > 
> > Tested-by: James Morse <james.morse@....com>
> > Reviewed-by: James Morse <james.morse@....com>
> > Reviewed-by: Reinette Chatre <reinette.chatre@...el.com>
> > Signed-off-by: Yury Norov [NVIDIA] <yury.norov@...il.com>
> > Signed-off-by: James Morse <james.morse@....com>
> > ---
> >  arch/x86/kernel/cpu/resctrl/internal.h | 28 +++++++-------------------
> >  1 file changed, 7 insertions(+), 21 deletions(-)
> > 
> > diff --git a/arch/x86/kernel/cpu/resctrl/internal.h
> > b/arch/x86/kernel/cpu/resctrl/internal.h
> > index eaae99602b61..25b61e466715 100644
> > --- a/arch/x86/kernel/cpu/resctrl/internal.h
> > +++ b/arch/x86/kernel/cpu/resctrl/internal.h
> > @@ -47,30 +47,16 @@
> >  static inline unsigned int
> >  cpumask_any_housekeeping(const struct cpumask *mask, int exclude_cpu)
> > {
> > -	unsigned int cpu, hk_cpu;
> > -
> > -	if (exclude_cpu == RESCTRL_PICK_ANY_CPU)
> > -		cpu = cpumask_any(mask);
> > -	else
> > -		cpu = cpumask_any_but(mask, exclude_cpu);
> > -
> > -	/* Only continue if tick_nohz_full_mask has been initialized. */
> > -	if (!tick_nohz_full_enabled())
> > -		return cpu;
> > -
> > -	/* If the CPU picked isn't marked nohz_full nothing more needs doing.
> > */
> > -	if (cpu < nr_cpu_ids && !tick_nohz_full_cpu(cpu))
> > -		return cpu;
> > +	unsigned int cpu;
> > 
> >  	/* Try to find a CPU that isn't nohz_full to use in preference */
> > -	hk_cpu = cpumask_nth_andnot(0, mask, tick_nohz_full_mask);
> > -	if (hk_cpu == exclude_cpu)
> > -		hk_cpu = cpumask_nth_andnot(1, mask,
> > tick_nohz_full_mask);
> 
> It seems that the cpumask_nth_andnot() function is no longer used anywhere,
> so it's better to remove it from ./include/linux/cpumask.h.

Yeah. Can you send a patch after this series will get merged? I'll
move it with my branch then.

Thanks,
Yury