linux-kernel - Re: [PATCH v5 7/9] blk-mq: use hk cpus only when isolcpus=managed

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Message-ID: <7beae89f-182d-4d88-a6a5-fffd4324dcda@suse.de>
Date: Mon, 13 Jan 2025 08:13:10 +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 7/9] blk-mq: use hk cpus only when isolcpus=managed_irq
 is enabled

On 1/10/25 17:26, Daniel Wagner wrote:
> When isolcpus=managed_irq is enabled all hardware queues should run on
> the housekeeping CPUs only. Thus ignore the affinity mask provided by
> the driver. Also we can't use blk_mq_map_queues because it will map all
> CPUs to first hctx unless, the CPU is the same as the hctx has the
> affinity set to, e.g. 8 CPUs with isolcpus=managed_irq,2-3,6-7 config
> 
>    queue mapping for /dev/nvme0n1
>          hctx0: default 2 3 4 6 7
>          hctx1: default 5
>          hctx2: default 0
>          hctx3: default 1
> 
>    PCI name is 00:05.0: nvme0n1
>          irq 57 affinity 0-1 effective 1 is_managed:0 nvme0q0
>          irq 58 affinity 4 effective 4 is_managed:1 nvme0q1
>          irq 59 affinity 5 effective 5 is_managed:1 nvme0q2
>          irq 60 affinity 0 effective 0 is_managed:1 nvme0q3
>          irq 61 affinity 1 effective 1 is_managed:1 nvme0q4
> 
> where as with blk_mq_hk_map_queues we get
> 
>    queue mapping for /dev/nvme0n1
>          hctx0: default 2 4
>          hctx1: default 3 5
>          hctx2: default 0 6
>          hctx3: default 1 7
> 
>    PCI name is 00:05.0: nvme0n1
>          irq 56 affinity 0-1 effective 1 is_managed:0 nvme0q0
>          irq 61 affinity 4 effective 4 is_managed:1 nvme0q1
>          irq 62 affinity 5 effective 5 is_managed:1 nvme0q2
>          irq 63 affinity 0 effective 0 is_managed:1 nvme0q3
>          irq 64 affinity 1 effective 1 is_managed:1 nvme0q4
> 
> Reviewed-by: Christoph Hellwig <hch@....de>
> Signed-off-by: Daniel Wagner <wagi@...nel.org>
> ---
>   block/blk-mq-cpumap.c | 65 +++++++++++++++++++++++++++++++++++++++++++++++++++
>   1 file changed, 65 insertions(+)
> 
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