linux-kernel - Re: [PATCH v8 10/12] blk-mq: use hk cpus only when isolcpus=io

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Message-ID: <6ba78d1d-19e9-41dc-bc91-3c9da537cabe@flourine.local>
Date: Mon, 8 Sep 2025 10:08:23 +0200
From: Daniel Wagner <dwagner@...e.de>
To: Hannes Reinecke <hare@...e.de>
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>, 
	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 v8 10/12] blk-mq: use hk cpus only when isolcpus=io_queue
 is enabled

On Mon, Sep 08, 2025 at 09:51:34AM +0200, Hannes Reinecke wrote:
> Wouldn't it be better to call 'cpumask_zero' before 'cpumask_and'?

I don't think this is necessary, from the docs :

  cpumask_and - *dstp = *src1p & *src2p

cpumask_and call bitmap_and which is:

static __always_inline
bool bitmap_and(unsigned long *dst, const unsigned long *src1,
		const unsigned long *src2, unsigned int nbits)
{
	if (small_const_nbits(nbits))
		return (*dst = *src1 & *src2 & BITMAP_LAST_WORD_MASK(nbits)) != 0;
	return __bitmap_and(dst, src1, src2, nbits);
}