linux-kernel - Re: [RFC PATCH v1 0/6] Introducing `wq_cpu

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Date:   Sun, 26 Feb 2023 07:01:41 -1000
From:   Tejun Heo <tj@...nel.org>
To:     Ammar Faizi <ammarfaizi2@...weeb.org>
Cc:     Chris Mason <clm@...com>, Josef Bacik <josef@...icpanda.com>,
        David Sterba <dsterba@...e.com>,
        Lai Jiangshan <jiangshanlai@...il.com>,
        Filipe Manana <fdmanana@...e.com>,
        Linux Btrfs Mailing List <linux-btrfs@...r.kernel.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        Linux Fsdevel Mailing List <linux-fsdevel@...r.kernel.org>,
        GNU/Weeb Mailing List <gwml@...r.gnuweeb.org>
Subject: Re: [RFC PATCH v1 0/6] Introducing `wq_cpu_set` mount option for
 btrfs

On Sun, Feb 26, 2023 at 11:02:53PM +0700, Ammar Faizi wrote:
> Hi,
> 
> This is an RFC patchset that introduces the `wq_cpu_set` mount option.
> This option lets the user specify a CPU set that the Btrfs workqueues
> will use.
> 
> Btrfs workqueues can slow sensitive user tasks down because they can use
> any online CPU to perform heavy workloads on an SMP system. Add a mount
> option to isolate the Btrfs workqueues to a set of CPUs. It is helpful
> to avoid sensitive user tasks being preempted by Btrfs heavy workqueues.
> 
> This option is similar to the taskset bitmask except that the comma
> separator is replaced with a dot. The reason for this is that the mount
> option parser uses commas to separate mount options.

Hmm... the allowed cpumasks for unbounded workqueues can already be set
through /sys/devices/virtual/workqueue/cpumask and also each individual
workqueue can be exposed in the matching subdirectory by setting WQ_SYSFS.
Wouldn't the proposed btrfs option be a bit reduandant?

Thanks.

-- 
tejun