linux-kernel - Re: [RFC PATCH v1 1/2] Documentation: btrfs: Document wq_cpu

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Message-ID: <Y/wUUBf9fuIAPsNw@debian.me>
Date:   Mon, 27 Feb 2023 09:24:16 +0700
From:   Bagas Sanjaya <bagasdotme@...il.com>
To:     Ammar Faizi <ammarfaizi2@...weeb.org>, Chris Mason <clm@...com>,
        Josef Bacik <josef@...icpanda.com>,
        David Sterba <dsterba@...e.com>
Cc:     Filipe Manana <fdmanana@...e.com>,
        Linux Doc Mailing List <linux-doc@...r.kernel.org>,
        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 1/2] Documentation: btrfs: Document wq_cpu_set
 mount option

On Sun, Feb 26, 2023 at 11:26:38PM +0700, Ammar Faizi wrote:
> +wq_cpu_set=<cpu_set>
> +        (since: 6.5, default: all online CPUs)

Why will the knob be introduced in 6.5 instead?

> +
> +        Btrfs workqueues can slow sensitive user tasks down because they can use any
> +        online CPU to perform heavy workloads on an SMP system. This option is used to
> +        isolate the Btrfs workqueues to a set of CPUs. It is helpful to avoid
> +        sensitive user tasks being preempted by Btrfs heavy workqueues.
> +
> +        The *cpu_set* is a dot-separated list of decimal numbers and ranges. The
> +        numbers are CPU numbers, the ranges are inclusive. For example:

"*cpu_set* is a dot-separated list of CPU numbers. Both individual
number and range (inclusive) can be listed".

> +
> +                - *wq_cpu_set=0.3-7* will use CPUs 0, 3, 4, 5, 6 and 7.
> +
> +                - *wq_cpu_set=0.4.1.5* will use CPUs 0, 1, 4 and 5.
> +
> +        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.

"... replaced by dots, since commas has already been used as mount
options separator".

> +        If *wq_cpu_set* option is specificed and the *thread_pool* option is also
> +        specified, the thread pool size will be set to the value of *thread_pool*
> +        option.

"If both options are set ..."

Thanks.

-- 
An old man doll... just what I always wanted! - Clara

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