linux-kernel - Re: [PATCH v7 01/10] lib/group_cpus: Add group_masks_cpus

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Message-ID: <f4ed094f-7370-4121-9df6-454411452751@flourine.local>
Date: Wed, 3 Sep 2025 14:42:10 +0200
From: Daniel Wagner <dwagner@...e.de>
To: John Garry <john.g.garry@...cle.com>
Cc: Daniel Wagner <wagi@...nel.org>, Jens Axboe <axboe@...nel.dk>, 
	Keith Busch <kbusch@...nel.org>, Christoph Hellwig <hch@....de>, Sagi Grimberg <sagi@...mberg.me>, 
	"Michael S. Tsirkin" <mst@...hat.com>, Aaron Tomlin <atomlin@...mlin.com>, 
	"Martin K. Petersen" <martin.petersen@...cle.com>, Thomas Gleixner <tglx@...utronix.de>, 
	Costa Shulyupin <costa.shul@...hat.com>, Juri Lelli <juri.lelli@...hat.com>, 
	Valentin Schneider <vschneid@...hat.com>, Waiman Long <llong@...hat.com>, Ming Lei <ming.lei@...hat.com>, 
	Frederic Weisbecker <frederic@...nel.org>, Mel Gorman <mgorman@...e.de>, Hannes Reinecke <hare@...e.de>, 
	Mathieu Desnoyers <mathieu.desnoyers@...icios.com>, linux-kernel@...r.kernel.org, linux-block@...r.kernel.org, 
	linux-nvme@...ts.infradead.org, megaraidlinux.pdl@...adcom.com, linux-scsi@...r.kernel.org, 
	storagedev@...rochip.com, virtualization@...ts.linux.dev, 
	GR-QLogic-Storage-Upstream@...vell.com
Subject: Re: [PATCH v7 01/10] lib/group_cpus: Add group_masks_cpus_evenly()

On Fri, Jul 11, 2025 at 09:28:12AM +0100, John Garry wrote:
> > +/**
> > + * group_mask_cpus_evenly - Group all CPUs evenly per NUMA/CPU locality
> > + * @numgrps: number of groups
> 
> this comment could be a bit more useful
> 
> > + * @cpu_mask: CPU to consider for the grouping
> 
> this is a CPU mask, and not a specific CPU index, right?

Yes, I've updated the documentation to:

/**
 * group_mask_cpus_evenly - Group all CPUs evenly per NUMA/CPU locality
 * @numgrps: number of cpumasks to create
 * @mask: CPUs to consider for the grouping
 * @nummasks: number of initialized cpusmasks
 *
 * Return: cpumask array if successful, NULL otherwise. Only the CPUs
 * marked in the mask will be considered for the grouping. And each
 * element includes CPUs assigned to this group. nummasks contains the
 * number of initialized masks which can be less than numgrps. cpu_mask
 *
 * Try to put close CPUs from viewpoint of CPU and NUMA locality into
 * same group, and run two-stage grouping:
 *	1) allocate present CPUs on these groups evenly first
 *	2) allocate other possible CPUs on these groups evenly
 *
 * We guarantee in the resulted grouping that all CPUs are covered, and
 * no same CPU is assigned to multiple groups
 */
struct cpumask *group_mask_cpus_evenly(unsigned int numgrps,
				       const struct cpumask *mask,
				       unsigned int *nummasks)

> > +	ret = __group_cpus_evenly(0, numgrps, node_to_cpumask, cpu_mask, nmsk,
> > +				  masks);
> 
> maybe it's personal taste, but I don't think that it's a good style to
> always pass through 'fail' labels, even if we have not failed in some
> step

I'd rather leave it as it is, because it matches the existing code in
group_cpus_evenly. And there is also alloc_node_to_cpumask which does
the same. Consistency wins IMO.