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From: Yury Norov <yury.norov@gmail.com>
To: Paul Gortmaker <paul.gortmaker@windriver.com>
Cc: Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
	Li Zefan <lizefan@huawei.com>, Ingo Molnar <mingo@kernel.org>,
	Thomas Gleixner <tglx@linutronix.de>,
	Josh Triplett <josh@joshtriplett.org>,
	Peter Zijlstra <peterz@infradead.org>,
	"Paul E. McKenney" <paulmck@kernel.org>,
	Frederic Weisbecker <fweisbec@gmail.com>,
	Rasmus Villemoes <linux@rasmusvillemoes.dk>,
	Andy Shevchenko <andriy.shevchenko@linux.intel.com>
Subject: Re: [PATCH 6/8] lib: bitmap: support "N" as an alias for size of bitmap
Date: Tue, 9 Feb 2021 15:16:10 -0800	[thread overview]
Message-ID: <CAAH8bW_fJi_PeHrXsPZzLtRP=-L99QJBXEvHkN9w6DBP-1FPWQ@mail.gmail.com> (raw)
In-Reply-To: <20210209225907.78405-7-paul.gortmaker@windriver.com>

On Tue, Feb 9, 2021 at 3:01 PM Paul Gortmaker
<paul.gortmaker@windriver.com> wrote:
>
> While this is done for all bitmaps, the original use case in mind was
> for CPU masks and cpulist_parse() as described below.
>
> It seems that a common configuration is to use the 1st couple cores for
> housekeeping tasks.  This tends to leave the remaining ones to form a
> pool of similarly configured cores to take on the real workload of
> interest to the user.
>
> So on machine A - with 32 cores, it could be 0-3 for "system" and then
> 4-31 being used in boot args like nohz_full=, or rcu_nocbs= as part of
> setting up the worker pool of CPUs.
>
> But then newer machine B is added, and it has 48 cores, and so while
> the 0-3 part remains unchanged, the pool setup cpu list becomes 4-47.
>
> Multiple deployment becomes easier when we can just simply replace 31
> and 47 with "N" and let the system substitute in the actual number at
> boot; a number that it knows better than we do.
>
> Cc: Yury Norov <yury.norov@gmail.com>
> Cc: Peter Zijlstra <peterz@infradead.org>
> Cc: "Paul E. McKenney" <paulmck@kernel.org>
> Cc: Rasmus Villemoes <linux@rasmusvillemoes.dk>
> Cc: Andy Shevchenko <andriy.shevchenko@linux.intel.com>
> Suggested-by: Yury Norov <yury.norov@gmail.com> # move it from CPU code
> Signed-off-by: Paul Gortmaker <paul.gortmaker@windriver.com>
> ---
>  .../admin-guide/kernel-parameters.rst         |  7 +++++
>  lib/bitmap.c                                  | 27 ++++++++++++++-----
>  2 files changed, 27 insertions(+), 7 deletions(-)
>
> diff --git a/Documentation/admin-guide/kernel-parameters.rst b/Documentation/admin-guide/kernel-parameters.rst
> index 682ab28b5c94..7733a773f5f8 100644
> --- a/Documentation/admin-guide/kernel-parameters.rst
> +++ b/Documentation/admin-guide/kernel-parameters.rst
> @@ -68,6 +68,13 @@ For example one can add to the command line following parameter:
>
>  where the final item represents CPUs 100,101,125,126,150,151,...
>
> +The value "N" can be used to represent the numerically last CPU on the system,
> +i.e "foo_cpus=16-N" would be equivalent to "16-31" on a 32 core system.
> +
> +Keep in mind that "N" is dynamic, so if system changes cause the bitmap width
> +to change, such as less cores in the CPU list, then N and any ranges using N
> +will also change.  Use the same on a small 4 core system, and "16-N" becomes
> +"16-3" and now the same boot input will be flagged as invalid (start > end).
>
>
>  This document may not be entirely up to date and comprehensive. The command
> diff --git a/lib/bitmap.c b/lib/bitmap.c
> index 6b568f98af3d..cc7cb1fca1ac 100644
> --- a/lib/bitmap.c
> +++ b/lib/bitmap.c
> @@ -530,11 +530,17 @@ static int bitmap_check_region(const struct bitmap_region *br)
>         return 0;
>  }
>
> -static const char *bitmap_getnum(const char *str, unsigned int *num)
> +static const char *bitmap_getnum(const char *str, unsigned int *num,
> +                                unsigned int lastbit)

The idea of struct bitmap_region is avoid passing the lastbit to the functions.
But here you do pass. Can you please be consistent? Or if I misunderstand
the idea of struct bitmap_region, can you please clarify it?

Also, I don't think that in this specific case it's worth it to create
a hierarchy of
structures. Just adding lastbits to struct region will be simpler and more
transparent.

>  {
>         unsigned long long n;
>         unsigned int len;
>
> +       if (str[0] == 'N') {
> +               *num = lastbit;
> +               return str + 1;
> +       }
> +
>         len = _parse_integer(str, 10, &n);
>         if (!len)
>                 return ERR_PTR(-EINVAL);
> @@ -580,9 +586,12 @@ static const char *bitmap_find_region_reverse(const char *start, const char *end
>         return end;
>  }
>
> -static const char *bitmap_parse_region(const char *str, struct region *r)
> +static const char *bitmap_parse_region(const char *str, struct bitmap_region *br)

It seems like you declare struct bitmap_region in patch 8, but use it
in patch 6.
Can you please reorder your patches and resubmit?

>  {
> -       str = bitmap_getnum(str, &r->start);
> +       struct region *r = br->r;
> +       unsigned int lastbit = br->nbits - 1;
> +
> +       str = bitmap_getnum(str, &r->start, lastbit);
>         if (IS_ERR(str))
>                 return str;
>
> @@ -592,7 +601,7 @@ static const char *bitmap_parse_region(const char *str, struct region *r)
>         if (*str != '-')
>                 return ERR_PTR(-EINVAL);
>
> -       str = bitmap_getnum(str + 1, &r->end);
> +       str = bitmap_getnum(str + 1, &r->end, lastbit);
>         if (IS_ERR(str))
>                 return str;
>
> @@ -602,14 +611,14 @@ static const char *bitmap_parse_region(const char *str, struct region *r)
>         if (*str != ':')
>                 return ERR_PTR(-EINVAL);
>
> -       str = bitmap_getnum(str + 1, &r->off);
> +       str = bitmap_getnum(str + 1, &r->off, lastbit);
>         if (IS_ERR(str))
>                 return str;
>
>         if (*str != '/')
>                 return ERR_PTR(-EINVAL);
>
> -       return bitmap_getnum(str + 1, &r->group_len);
> +       return bitmap_getnum(str + 1, &r->group_len, lastbit);
>
>  no_end:
>         r->end = r->start;
> @@ -636,6 +645,10 @@ static const char *bitmap_parse_region(const char *str, struct region *r)
>   * From each group will be used only defined amount of bits.
>   * Syntax: range:used_size/group_size
>   * Example: 0-1023:2/256 ==> 0,1,256,257,512,513,768,769
> + * The value 'N' can be used as a dynamically substituted token for the
> + * maximum allowed value; i.e (nmaskbits - 1).  Keep in mind that it is
> + * dynamic, so if system changes cause the bitmap width to change, such
> + * as more cores in a CPU list, then any ranges using N will also change.
>   *
>   * Returns: 0 on success, -errno on invalid input strings. Error values:
>   *
> @@ -660,7 +673,7 @@ int bitmap_parselist(const char *buf, unsigned long *maskp, int nmaskbits)
>                 if (buf == NULL)
>                         return 0;
>
> -               buf = bitmap_parse_region(buf, &r);
> +               buf = bitmap_parse_region(buf, &br);
>                 if (IS_ERR(buf))
>                         return PTR_ERR(buf);
>
> --
> 2.17.1
>

  reply	other threads:[~2021-02-10  1:31 UTC|newest]

Thread overview: 31+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2021-02-09 22:58 [PATCH v4 0/8] support for bitmap (and hence CPU) list "N" abbreviation Paul Gortmaker
2021-02-09 22:59 ` [PATCH 1/8] lib: test_bitmap: clearly separate ERANGE from EINVAL tests Paul Gortmaker
2021-02-09 22:59 ` [PATCH 2/8] lib: test_bitmap: add tests to trigger ERANGE case Paul Gortmaker
2021-02-10 16:27   ` Andy Shevchenko
2021-02-09 22:59 ` [PATCH 3/8] lib: test_bitmap: add more start-end:offset/len tests Paul Gortmaker
2021-02-09 22:59 ` [PATCH 4/8] lib: bitmap: move ERANGE check from set_region to check_region Paul Gortmaker
2021-02-10 16:28   ` Andy Shevchenko
2021-02-09 22:59 ` [PATCH 5/8] lib: bitmap: pair nbits value with region struct Paul Gortmaker
2021-02-10 16:34   ` Andy Shevchenko
2021-02-09 22:59 ` [PATCH 6/8] lib: bitmap: support "N" as an alias for size of bitmap Paul Gortmaker
2021-02-09 23:16   ` Yury Norov [this message]
2021-02-10 15:58     ` Paul Gortmaker
2021-02-10 16:49       ` Andy Shevchenko
2021-02-12  1:24         ` Yury Norov
2021-02-21  8:07           ` Paul Gortmaker
2021-02-09 22:59 ` [PATCH 7/8] lib: test_bitmap: add tests for "N" alias Paul Gortmaker
2021-02-09 22:59 ` [PATCH 8/8] rcu: deprecate "all" option to rcu_nocbs= Paul Gortmaker
2021-02-10 16:26 ` [PATCH v4 0/8] support for bitmap (and hence CPU) list "N" abbreviation Andy Shevchenko
2021-02-10 17:57   ` Paul E. McKenney
2021-02-10 23:50     ` Yury Norov
2021-02-11  0:23       ` Paul E. McKenney
2021-02-12  0:23         ` Yury Norov
2021-02-12  0:38           ` Paul E. McKenney
2021-02-21  8:02       ` Paul Gortmaker
2021-02-11 11:04     ` Rasmus Villemoes
  -- strict thread matches above, loose matches on Subject: below --
2021-02-21  8:08 [PATCH v5 " Paul Gortmaker
2021-02-21  8:08 ` [PATCH 6/8] lib: bitmap: support "N" as an alias for size of bitmap Paul Gortmaker
2021-01-26 17:11 [PATCH v3 0/8] support for bitmap (and hence CPU) list "N" abbreviation Paul Gortmaker
2021-01-26 17:11 ` [PATCH 6/8] lib: bitmap: support "N" as an alias for size of bitmap Paul Gortmaker
2021-01-26 21:37   ` Andy Shevchenko
2021-01-26 21:41     ` Andy Shevchenko
2021-01-27 17:57       ` Yury Norov
2021-01-27  8:20     ` Paul Gortmaker

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