linux-kernel - Re: [PATCH v5 8/9] blk-mq: issue warning when offlining hctx with online isolcpus

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Message-ID: <53654909-609a-4385-82dc-6cab3dd5e611@suse.de>
Date: Mon, 13 Jan 2025 08:14:08 +0100
From: Hannes Reinecke <hare@...e.de>
To: 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>
Cc: "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>, 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 v5 8/9] blk-mq: issue warning when offlining hctx with
 online isolcpus

On 1/10/25 17:26, Daniel Wagner wrote:
> When isolcpus=managed_irq is enabled, and the last housekeeping CPU for
> a given hardware context goes offline, there is no CPU left which
> handles the IOs anymore. If isolated CPUs mapped to this hardware
> context are online and an application running on these isolated CPUs
> issue an IO this will lead to stalls.
> 
> The kernel will not schedule IO to isolated CPUS thus this avoids IO
> stalls.
> 
> Thus issue a warning when housekeeping CPUs are offlined for a hardware
> context while there are still isolated CPUs online.
> 
> Signed-off-by: Daniel Wagner <wagi@...nel.org>
> ---
>   block/blk-mq.c | 43 ++++++++++++++++++++++++++++++++++++++++++-
>   1 file changed, 42 insertions(+), 1 deletion(-)
> 
Reviewed-by: Hannes Reinecke <hare@...e.de>

Cheers,

Hannes
-- 
Dr. Hannes Reinecke                  Kernel Storage Architect
hare@...e.de                                +49 911 74053 688
SUSE Software Solutions GmbH, Frankenstr. 146, 90461 Nürnberg
HRB 36809 (AG Nürnberg), GF: I. Totev, A. McDonald, W. Knoblich